ohnson, Evinrude, OMC, outboard motor, outboard motor repair, 9.9, 15 hp, year of manufacture, powerhead, piston, water pump, carburetor, long shaft, 15 hp conversion, sailmaster


Maintaining Johnson/Evinrude 9.9 & 15 hp 2 cycle outboards

1974 – 2007   (Lower Unit / Waterpump Rebuild)   
 



Definitions :  The words lower unit, gearcase and gear housing can be used interchangeably in the marine industry.  The word FOOT is also slang for the lower unit - used mostly in the South.  And you will sometimes see the "leg" mentioned, which could stand for the outer exhaust housing even to include the lower unit if it is integral

Shifting Problems : Any time you may have a shifting problem, do not immediately question the gearbox, ESPECIALLY if you happen to be using a motor that is hooked up to remote controls.  The cables can become seized internally, or possibly stretched, even become unhooked from the motor.  There are adjustments of the cables at the throttle/shift control ends.

If you do have remote controls, disconnect them from the motor and try shifting the motor manually at the motor as a test.

Do Not Force Shifting Lever : One thing to be aware of on these motors, is that the clutch dogs in the gearcase's transmission are rather large in relationship to some other models.  This is good in that you most likely will not experience the motor jumping out of gear because of worn clutch dogs if the linkage adjustment is not properly set.  But also at the same time, it means that you should NOT TRY TO FORCE the shift lever into a gear while the motor is NOT RUNNING.  You could very well break the shift lever, especially the newer plastic levers, or bend some of the linkage if the older metal lever.  If you HAVE to place the transmission in gear with the motor not running and the shift lever does not want to engage, try slowly pulling on the starter rope just enough to allow the clutch dogs to mesh in the gears.   When you find this spot you will be able to move the shift lever from forward / neutral and then into reverse.

Slipping Out of Gear : Here could be a situation where the actual gearbox is OK, just the linkage to the motor's shifting arm is out of adjustment.  In the photo below, the motor is shifted into reverse, the red arrow is pointing to a notch on the rotating shifting detent cam.  However the spring detent arm at the left is not into the notch below it, which could allow the gears to pop out of gear during a running situation.

To adjust this, the blue arrow is pointing to a threaded rod from the shifting linkage that needs to be threaded out of the black plastic clevis, so the three are synchronized (gear clutch dog, shifting lever and these detent notches).

Here we see a out of adjustment shifting adjustment rod

Actual Removal of Gearcase to Access the Water Pump :  If the motor has been used in saltwater to any degree, I will guarantee that at least a few of the bolts will be seized in and will be twisted off.  I will cover this in the troubleshooting  section however.   Have the motor mounted either on the transom of the boat, on a motor stand or saw horses.  It also will make a slight difference in the procedure whether the motor is a long shaft or not.  There are 6 stainless, 1/4” bolts with 3/8” heads that come in from the bottom and are bolted up into the exhaust housing assembly.  If it is a short shaft, they are the only ones there.  If however it happens to be a longshaft, there is a 5” extension, or if a Sailmaster a 10" extra long extension between the lower unit and this housing.  If so, then remove the upper 6 bolts for access to the shift linkage coupler.  The lower 6 bolts attach this extension to the lower unit which would need to also be removed to access the water pump. 

When you get these 6 bolts removed, the gear case unit should drop down about 1/2”.  If it does not you may have to tap it with a plastic mallet.  Shift the gearshift into reverse to pull the lower shifting rod up allowing access to the connector retainer bolts.  When the lower unit does slide down, there will be, inside the housing in the front right hand side, a connector that is a strap with 2, ¼” tapped holes top and bottom.  Shift the gearshift into forward, allowing the gearcase to drop down enough to access the connector bolts.  In these holes are 2 bolts that are screwed in sideways connecting the upper and lower shifting rods.  These bolts go in a threaded hole in the connector, which has a vertical groove for the shifting rods, and the bolts go into the connector with the rods which have a groove that the bolts slide into it hold the rods in place.  Remove only the top screw.  It has a 3/8" hex head and also a screwdriver slot.  If you need to replace it, get a stainless steel 1/4" X 28TPI (National Fine) 1/2" long and hacksaw a screwdriver slot in the head.  However, make it wide enough to be able to use a decent sizes screwdriver blade on.  Once this bolt is removed the gearcase unit can be moved downward and off the midsection exhaust housing.

Showing the shifting rod screw that needs to be removed to disassemble the unit.  This photo is of a short shaft motor

If after you remove the above shifting rod coupler bolt AND YOU CAN NOT get the driveshaft to come loose from the crankshaft splines up inside the housing and slide down and off, your only way to separate the exhaust housing from the lower unit is to drive a couple of wooden wedges in between the two, forcing them apart.  In the process, the driveshaft with the water pump impeller key will be forced out through the top of the plastic water pump housing, usually breaking the top of the pump housing.  You might luck out in that it only ruins the water pump's top seal.

It just about has to come off, as there is not enough room to assemble everything off the bottom and still tighten the water pump housing screws.  The only other alternative is to pull the powerhead to get to it.  But that will probably be harder to accomplish the goal.

Once the driveshaft key has been pulled through the water pump, the driveshaft will now just slide out of the splines of the gears in the lower unit and out of water pump.   If it broke the plastic housing, you may need a new housing, or at least probably a new seal #0318972. 

Only thing to remember is if you now tip the lower unit, gear oil will leak (RUN) out the hole where the driveshaft was.

To pull the driveshaft from the stuck section in the crankshaft, you may have to tip it upside down and pour penetrating oil in.   If you just poured oil in, it would have to be over 2 1/2" inside before it would get up over the raised boss that the shaft goes into.  A better way would be to again tip it up, but at a slight angle, pour a slight amount of penetrating oil ONTO the shaft, allowing the oil to run down the shaft so it would be able to go up inside the raised boss the shaft is in on the lower part of the powerhead.  Pour enough in so that you are sure it may be getting to the spline.  Let this set for a few days.   BTW one of the best penetrating oils is a 50/50 mix of Automatic Transmission Fluid and Acetone.  A second  choice would be hydraulic brake fluid.  

Then you can clamp a Vise Grip plier onto the shaft (at a location where no seal or impeller will be).  Using a big hammer, pound on this Vise Grip trying to drive it out of the splines in the crankshaft.  You might mark it somewhere so you would have an idea if it starts to move.  Try to pound it out, let it set again.   Pound on the lower end, trying to at least move it a tad bit.  Pound on the pliers again.  You do not really care if it mars the shaft IF it is in a location where no seals are located as you can file that down later . 

You may have to beat on it repeatedly over a few days and all the while trying to rap it also sideways to loosen the rusted in connection.  When you put it back be sure to grease the splines with waterproof (boat trailer bearing) grease.

You will get it off, but it may take a while and then will have to file off the marks on the shaft as the water pump housing and impeller has to slide over this upper section of the shaft. 

Unless you've damaged those non-critical areas, you can just file the marks down and use it as is.    A lot of machine shops can spray new metal on minor corrosion pits (and Vice-Grip marks), then regrind to the original outside diameter.   Replacement shafts are around $170, so reworking your's if the functional ends are OK is readily acceptable.

Here, showing the powerhead removed from the exhaust housing for clearer understanding, with the driveshaft as it would be when stuck & upside down

Clean Out & be Sure the Front Cavity & Drain is Clear :  When you get the lower unit separated from the midsection look at the large forward cavity in the gear case unit.  This cavity is only accessible from the top when the gear case is removed.  This cavity has a drain hole coming out just above and on the left hand side of the rounded gearcase boss.  If the motor has been used near saltwater, this whole inner cavity can become plugged with salt/aluminum corrosion residue.  The shifting rod runs down into the gear case in the middle of this cavity.  Do not remove this shifting rod at this time, as it has a rubber O-Ring seal around the lower end to keep the water out.  If you unscrew this shaft, take it out before you clean this cavity, salt and debris will fall inside the gearbox. And you might have problems getting the threaded end of the shaft aligned back so that it will start into the threads of the shifting yoke inside the lower unit.

You may have to use a long screwdriver or something similar to dig out much of this debris.  This salt/aluminum debris can be packed in very hard.  Wash it out, keep digging, as there is quite a large deep cavity here.  The internal drain hole to the outside drain hole is in the very forward part of this triangle.  You will also need to weld a 1/4" extension on a standard 3/16” drill bit that will be about 9" overall.  Use it on a drill motor to drill out this crap, especially down to the drain hole.

For the older motors, you will then need an 1/8" drill to clean out from the outside hole into the inner cavity, location as shown by the arrow in the LH photo below.  On the later motors of late 1980's on this hole was increased to 1/4".   When you get this cavity clean, wash it out with water, and observe whether the water runs out the outer drain hole.

In the RH photo below, the water pump housing is what you see attached by the 4 bolts.  The arrow is pointing to the shifting rod coupler visible on the small shaft.  

Drain hole for the cavity from the outside

This is what it should look like. 

As you can see from the LH photo below, the housing is cracked and even a chunk of the outer housing missing.  This in itself may not effect the operation of the motor because inside this particular area is just a void and not into the gearbox itself, UNLESS there are other internal corrosion possibly into the gearcase.   The small round hole is the drain hole shown in the previous photo above.  RH lower photo, unburned gas/oil from excess idling during trolling PLUS salt corrosion accumulated here.   If the drain hole was clear, this oil would drain out and not allow this much build-up.

You may think that since you flush your motor that with muffs each time, that this cleans this inside cavity as well.  Not for this cavity.  If the cavity and corresponding drain hole is clear, when you remove the motor from the water, about 1 cup of water should run out this outer drain hole.  When removal from the water, this can drain water out for a couple of minutes.  It is recommended that you find a small nozzle, back-flush water into the outer drain hole each time you flush the motor.  The later models increased hole from 1/8"size to about 1/4" and it would be recommended that you also do this, in that the factory must have decided the smaller hole may have been detrimental as shown by the 2 photos above.
 

Here salt corrosion built up inside the front housing which popped holes in the housing. Salt corrosion with a mix of unburned exhaust oil  because of a plugged drain hole.  This was on a longshaft motor

Another thing you may encounter is corrosion devouring the aluminum at the water pump base.  If the aluminum (usually in the front) of the base under the water pump is deteriorated, you can clean it up by sandblasting, then build it up with the epoxy called J-B Weld.  There has to be material there otherwise the flow of water being sucked up thru the intake screens, then into the housing below the bottom of the water pump will not direct the water in the right place.   This can then greatly effect the efficiency of the water pump.

Shown below is a cure for this corroded area.  Lathe turn a stub shaft that just goes into the shaft seals on the bottom, also fit the upper corroded area.  The drive-shaft size is 1/2" and the outer diameter of the seal is 1 .125".  Once this stub shaft is made, lubricated with Vaselene to keep the J-B Weld from adhering, mix the epoxy, pushing it into place, wait for the curing to take place.  Once cured, the bond to the stub shaft (if there is any) can be broken loose by rotating the stub shaft.  If you are replacing the upper shaft seals, you will have to be sure that this new epoxy area is slightly larger than the seal OD as you do not want to break the epoxy that you just put in.  The corrosion will not usually be low enough into the housing to effect the outer seal surface.   When cured, file the epoxy flat with the top of the housing.

The photos below show the stub shaft on the left.  On the right photo, the built up epoxy is marked in purple and identified by the arrow A.   Arrow B shows the shifting rod seal bushing in place.  Note, that there needs to be an opening at the rear into the rectangular hole coming from the water intake.  Do not mistake material being gone here as being corroded out.  If you build it up here also you have effectively blocked all water into the water pump.

A lathe turned stub shaft as described above Water pump base rebuilt with J-B Weld shown in purple

Water Pump :  The operation of most marine water pumps using a rubber vaned impeller is, the cavity between the vanes is what makes it pump water.  As the off-center impeller rotates, the cavity enlarges, drawing in a gulp of water.  As it continues to rotate, the cavity becomes smaller, and squeezes the water out and up the water tube to the powerhead.

These motors are equipped with a plastic/Nylon bodied water pump housing.  There is also a stainless bottom plate, this plate has to be positioned with the suction hole in the proper location/relationship as indicated in the photos.   If you are just replacing the impeller, you can tell which way is up by observing the wear of the impeller on this plate.   The impeller fits in this stainless cup liner which gives a very long lasting situation.   In most cases you will never need to replace the water pump assembly, just the impeller.   Sometimes the rubber impeller becomes un-bonded to the metal hub making for an inoperative pump.

Things to look for after the water pump is removed are, the impeller can take on a curl rather than have the blades snap straight outwards when removed from the housing.  It may have also picked up some sand or some other type abrasive material which has created a scoring in the lower impeller plate and/or upper housing.  That scoring alone would have a tendency to create a air pocket creating inefficiency in the pump. 

On the left, Bombardier water pump kit complete #394711.  Fits all Johnson and Evinrude 9.9 and 15hp 2 stroke motors from 1974 thru 2007 and 4 stroke 8, 9.9 and 15hp motors from 1995 thru 2001. 

This complete kit, with all needed parts to completely replace the water pump and instructions. It sells for about $40 at most dealers.

On right is just the new impeller, which usually sells for about $12.

On these motors, the water goes to the outer water jacket first, the overboard water indicator line comes off the lower jacket (closest to the pump's input location).  This overboard water indicator (tell tale) will have water first, before going into the rest of the motor.  Therefore if you do not have water coming out of this indicator hole, and YOU ARE SURE THAT THERE ARE NO BLOCKAGES, things pretty well point to your water pump IS NOT WORKING.  

One rule of thumb is: if the engine overheats and the water pump impeller doesn't look like it just came out of the box, replace it --- then should the problem still persist, go further into the system as needed.  Of course be sure the outlet tube and grommet is fitting correctly.  But you have eliminated the most likely source of the problem to start with.

Shown below on the left is the water pump with the impeller on the driveshaft.  During functioning the water is drawn into the housing in a slot in the lower plate of the water pump, (not shown here) but this slot is at the lower side of this photo.   The vanes are not as compressed allowing the water to be sucked into the cavity.   As the impeller turns on the driveshaft, the vanes compress as the cavity is not centered , but offset or eccentric.  This offset forces the water from the rotating impeller out the gap seen on the top of the cavity and up into the copper tube which is located in the 1/2" round hole in the top of the pump housing.  Here the tube is secured and sealed by a rubber grommet in the top of the water pump.

When the motor is running, the water in the water pump housing is pushed by the rubber vaned centrifugal impeller upward and into the 3/8" copper supply tube up into the powerhead. 

On the photo below, the RH is a new water pump impeller.  Seen here is the drive slot in the bottom for the impeller key into the driveshaft.

As said before, this is a centrifugal pump, this means that the impeller is a rubber vaned insert setting inside of a stainless steel housing.  Again the impeller is offset to one side so that when the water comes into the pump housing at the widest part around the impeller and as the impeller turns the water is compressed and then forced out on the other side.   This is illustrated by the LH photo below.

The outer edges of the vanes are not the only significant part of the water pump impeller as the circular rubber rings on both sides also act a seal, keeping the water trapped between the vanes.

In the right hand photo below, you can see the semi-circle slot, which is the water inlet into the impeller chamber.  The housing has a shallow slot on the upper part of the stainless steel cup and housing in this photo.  This allows the water to be pushed out and into the chamber where the copper tubing carries the water up to the powerhead.

Water pump viewed from bottom side New impeller Here is the housing & lower plate pivoted to the right

If you tear it apart and a vane or two are missing, or even the ends partly worn off, this could not be good, as where did these chunks of rubber go to?  They may stuck up inside the supply tube to the motor, or they if happened to get by that location, could be inside the water passages in the block/head or plug the thermostat.

In the photo below you will see 2 bad impellers.  The one on the right has taken a set  from being in the housing so long that it would not be really effective.  What you can not see is that the inner metal core that has the keyway in it has become about 1/2 unbonded from the rubber.  This core is made round. 

The impeller on the left has a hexagon core that has become completely unbonded.  It however may function (for a while) until it disintegrates.  If you tear a water pump down and find a hexagon section on the driveshaft, this is what you have.  Don't get excited if your new impeller does not look like the one that came out, just remove the metal, clean the shaft and proceed with the repairs.

Both 9.9/15hp impellers, but of a different vintage showing the different hubs.  The one on the right has obviously taken a set & needed replacement

The driveshaft may have a O-Ring around it on the splines that engage the motor crankshaft.  The earlier motors had a groove around the shaft for this O-Ring, while the newer ones apparently had the O-Ring in a internal groove in the lower end of the driveshaft.  The O-Ring was to help keep rust from forming in the crankshaft splines, seizing the driveshaft to the crankshaft.   But if you just smear some marine boat trailer spindle grease on the shaft splines when you reassemble, this serves the same purpose.  They found that on rare occasions that IF you hit something really hard the rubber prop hub may not absorb all the impact and the driveshaft can twist off at this groove, making removal of the broken stud, so the groove was abandoned.

If this O-Ring is on the shaft, remove it until you are ready to re-install the parts.   Don't worry about it if your shaft does not have a groove in the upper splines, just be sure to apply some grease on these splines when reassembling.

Now on the top of the gear case unit, you will find 4 bolts holding the water pump on with the driveshaft going thru this pump housing.  The pump housing will plastic/nylon.  Newer units will have brass sleeves around the bolt holes to eliminate any problem of over tightening, cracking the pump body.

Unscrew these 4 bolts and slide the water pump housing up and off the driveshaft.  The front 2 screws are longer than the rear ones for the original units.  Keep this in mind when you reassemble the unit.   Later pumps used the same length screws for all of them.   If you purchase a new water pump kit it includes the impeller, seals, O rings and a new housing it will come with 4 new  shorter screws as the new housing front bolt bosses are lower, the same height as the rear.   Make note of which direction the impeller vanes are facing, as you need to install the new impeller the same way, otherwise it will not pump right.  Now also there will be a key that holds the impeller to the shaft.  Save this also for reassembly.

If you take it apart and the impeller appears still intact, you should consider inspecting it further, as it is not uncommon for the inner hub to become unbonded from the rubber impeller, allowing the hub to spin inside the impeller rubber.   Some of these metal hubs are round while other brands are hexagon.  Also some aftermarket impellers can be thinner than the originals, not sealing on the sides, sucking air, creating erratic pumping.

When assembled in the pump housing and bolted onto the lower unit the driveshaft and impeller rotates clockwise as does the motor.  Since the pump housing is smaller than the impeller, the vane tips need to be facing in a counter-clockwise position as they are FOLLOWING the rotation of the driveshaft which forces the vane tips backwards.

The motor has to be submerged in water above the level of the water pump.  The impeller pulls the water in the pump unit and then pumps it up into the engine.

It is recommended you replace the water pump to outlet tube grommet as well.   This grommet is held in place by 2 "ears" on the sides that snap into matching holes in the top of the water pump outlet hole.

If you order a BRP #394711 water pump repair kit (shown in the photo above) among all the other parts there will be 3 rubber grommets, one is taller and flared than the other as seen in the photo below.   There is another taller but smaller dia. grommet that is designed for the 4 stroke motors.  If you purchase an aftermarket kit like Sierra, this 4 stroke grommet may not be included.

These same water pump kits are used on all OMC models of 9.9 and 15hp motors from 1974 on to 2005 and then the 4 stokes after that.  

The regular shorter grommet # 302497  is designed for the 15" or regular shortshaft length motors, while the taller grommet # 327035 is designed for the 20" longshaft and 25" extra longshaft models.  The reason for the longer grommet, is if you look at it, the taller body has the inner hole with more of a long taper, allowing the water pump outlet pipe better alignment (especially since it is buried deep inside the longshaft extension and out of sight during final installation) the tube has to automatically align.

Now to confuse the issue, the printed factory parts list is WRONG, listing the #327035 as for the 15" shortshaft and the #302497 for the 20" unit.  THESE DISCRIPTIONS OF THE LENGTH TO BE USED ON, ARE JUST REVERSED IN THE FACTORY PARTS MANUAL.  And some of the aftermarket suppliers also have it wrong, OR the image is so distorted that it is pretty hard to clearly identify which one is which.  But if you go to Marine Engine.com   they have it right on their online parts catalog.

To verify this, I made a special trip to a OMC marine mechanic and had him pull one each of these numbered parts.  So again YES, the regular shorter grommet # 302497  is designed for the 15" or regular shortshaft length motors, while the taller grommet # 327035 is designed for the 20" and 25" longshaft models.

Johnson/Evinrude OMC Grommet #0302497 is equivalent to aftermarket parts: 18-3329 Sierra Marine, 878863 Mercury Marine, 9-43603 Mallory Marine, 86492 GLM
Johnson/Evinrude OMC Grommet #0327035 is equivalent to aftermarket parts: 18-2392 Sierra Marine, 878816 Mercury Marine, 9-43615 Mallory Marine, 86496 GLM

Here the bag shows the correct number for the longshaft (20") grommet Here is the factory parts list, but it is wrong
Click on the above thumbnail top see full size

Some mechanics may install the longer longshaft grommet for better alignment in the short shaft motors thinking this is an improvement which pretty well eliminates any misaligned, folded over grommet problem, yes it helps.  Some of the water pump kits only supply the parts, with no identification of these grommets.  However if you do so, the grommet is tall and wide enough at the top where the water tube goes in that it will come in contact with the bottom of the exhaust housing, sealing off the exhaust water cavity drain holes around the tube off. 

This can prevent any water from draining back into and then out of the lower unit exhaust area via the oversized hole the copper water tube passes upward through from the water pump.   There should be minimal water BUILDUP in this area, just enough to cool the housing.  

What will happen is that the motor will run well for a while, and usually fine at an idle, but when you give it some throttle, it may hesitate, even sound like it is coughing.  Yes, it is because water is backing up inside the exhaust, choking any expedient exhaust gas outlet with the only real exhust releif at the blubber hole on the rear upper section of the exhaust housing.  This will usually effect more dramatically the early 9.9/15hp motors that use the square exhaust tube.   The later motors that use the round exhaust tube that is not sealed at the lower end at the lower unit should not be afflicted by this problem. 

Another thing this could do is to captivate water inside this area when you put the motor away for the winter and those who live in climates that freeze in the winter, AND there is any water trapped above this plate, this water could freeze, expand and break the housing.

NOW if you do insist on using this longshaft better alignment grommet on shortshaft motors, you can modify the housing by drilling 2 holes about 3/16" dia. holes in the exhaust housing plate on each side of the grommet location to ensure any entrapped water will drain out of that cavity as shown in the photo on the right below.  Shown below are the placement of new drain holes.  However location seems to be pretty critical as there is a recess on the outer housing to accommodate the lower rubber housing mounts and the inner boss.  These are my second try before getting them into the cavity above, so location is pretty critical.

Depending on the year of motor, the lower unit (as seen in the RH photo below) can have different water escape around the copper tube from the water pump.  The photo below shows a couple of "key" type slots on each side of this tube as it enters the housing, this photo is of a 1979 motor.  Motors in at least the 74-76 range have a different water escape in that the hole where the tube enters is simply made oversize by about 1/8".

At the left is a longshaft grommet # 327035, with a shortshaft #  302497 in the center & on the right is a shortshaft style that is damaged, folded over & restricting flow.   Note the "retaining ears" on them. Shown here by the red arrows is the location I found that  should work.  Anything forward & out will miss the narrow cavity above.  You can see the 2 drain slots on the sides of the copper water tube that can be blocked by a longshaft grommet when used on a shortshaft exhaust housing

On these early 1974-1976 motors the outlet water just exited from the block behind the exhaust tube and into this chamber to cool the exhaust tube and to provide a bit of back pressure to blubber enough exhaust gas/water to tell the water pump was working.  Later the exhaust water was diverted down part way by a short copper tube.

There is also a large neoprene O-Ring that is slid over the top of the water pump housing.  This helps align the lower unit and water pump into the mid section housing and to keep water from entering the driveshaft cavity.  

There is a seal on top of the water pump housing which the driveshaft goes thru.  This seal is needed to make a complete seal on the top of the water pump, otherwise UNLESS the water pump is totally submerged you will have erratic pumping due to air ingestion.  This is also to isolate any water from backing up inside the driveshaft channel, enough to (if it was saltwater) to corrode the splines of the upper driveshaft/crankshaft when later removal was required.

Exhaust Housing :  These have been modified over time to accommodate exhaust improvements.  The early models up until about 1981 when the 15hp motors were fitted with the round tuned exhaust tubes had the square exhaust tubes sealed on the bottom with a rubber ring.  Then about 1990 all, even the 9.9s were fitted with the round exhaust tube.  The later round tubes were not sealed at the bottom.  As shown in the RH photo below, the tube stops about 1" above this plate that has the two approximately 5/8" diameter relief holes in.

Notice the differences in the relief clearances around the water tubes.  The 74 has just excess slop around the tube, but can create a problem on realignment of the tube when replacing a impeller if the tube is not truly centered because of the limited viewing of this much needed alignment when assembling the lower unit to the exhaust housing.  The 79 has a slightly smaller hole for better tube alignment and has side slots for water escapement.  While the 92 appears to be a combination of both the 74 and 79.

1974 exhaust housing

1979 exhaust housing

1992 exhaust housing

You will notice in the LH photo below that the round exhaust tube is about 1" shorter and as indicated above it does not bottom out as the square bottom rubber sealed tube.

You will also notice in the RH photo below that the early square tube has no provision for exhaust water as it just belched behind (to the left) of the LH image.  The later units were fitted with a actual water tube that was about 6" long as seen in both photos.  Water inlet tubes stayed the same.

You could probably use the later round exhaust tubes in the earlier housings with little consequences as when on a boat and in the water, the water itself will be up to about that baffle level, which would in turn create some backpressure.  However it may be best to do some JB Weld buildup on the bottom of the block to accommodate the new outlet tube.

RH side view of 9.9 hp square & 15 hp round exhaust housings Early 9.9 exhaust housing on left & later 9.9 & 15 hp "tuned" exhaust housings on right, top view

Flushing With Garden Hose : If you have been having water problems, you may consider at this time, fabricating a garden hose adapter to the copper water supply tube leading to the powerhead.  This is made from a 5/16" or 3/8" ID rubber or vinyl tube attached to a 3/8" barbed fitting that is then screwed into pipe bushings and then into a garden hose to pipe end.   You can hose clamp the rubber/vinyl tube onto the barbed fitting.  Then with the lower unit off the exhaust housing, hose clamp the loose end onto the motor's 3/8" copper tube. 

Without the motor running, turn on the garden hose water supply, starting slowly until you see what is happening.  If nothing, or very little water exits the overboard tell tale hole, poke the small wire up there to clean it out again.  On the early 1974 motors that did not have a overboard tell tale hole, this method will not work.  Turn the water on full force and see if you can force debris, salt or sand out using this method.   If there is a blockage somewhere, you will not get any (or very little) out the rear blubber hole if it is a pre 1977 or the tell tale hole if a later model.

Water-jacket  flush adapter

 If you have some flow out the tell tail hole, but there is considerable debris, you may have to constantly poke the wire into the pee hole to clear this exit hole.  I have also made a 3/16" wire into a crank handle type thing and flattened the upper end.  You can poke it up the motor supply tube, rotate it to see if any debris is in this tube.   If this does not do it and if it is apparent that there may be considerable debris inside, or a blockage somewhere, then you should probably remove the head itself as on these motors prior to 1987 it is easier than just the thermostat cover.   Now remove the thermostat cover and  you can see if there is a blockage or bad thermostat.

One thing about using this method is that you can isolate if it is the water pump, or a blockage inside the powerhead or water jacket passages.

Reassembly of Water Pump :  One thing that many who just replace the impeller overlook, is the seal in the top of the water pump housing.  If that seal that seals around the driveshaft has deteriorated, replacing a impeller may not be as efficient as you would hope.  Plus, excess water could be pushed up the driveshaft, doing things that the motor was not designed to handle.

Place the new impeller in the water pump housing with the vanes
ALL
pointing in the same direction as when you took the old one out.  If you forgot, remember that the motor rotates in a clockwise direction, therefore the vanes need to be pointing in the opposite direction as the motor is rotating as the rotating shaft will force the vanes back.  Also take into consideration that you maybe assembling this unit upside down before you slide it onto the driveshaft.  If you get them in wrong, it possibly will not hurt, as when the motor is started and ran at a high RPM, the centrifugal force of the rotation more than likely establish them in the right relationship anyway.

It is a good idea to put a slight amount of grease on the impeller vanes at this time also. The plastic housing pumps have a stainless steel inset that the impeller rotates inside of.  This insert has to also be aligned and in the right place when assembling the upper housing.   The repair manual for my motor indicates that, when installing a new impeller, the vanes should be greased and the housing should be installed while rotating the drive shaft clockwise. That takes care of the proper orientation.  You will have to slightly force the impeller to one side as the housing is not centered but is eccentric with the shaft to make the impeller pump water.  With the impeller in the stainless cage, slide the pump housing and  impeller unit onto the shaft.  Again be SURE that ALL the vanes are pointing in the same direction. Remember the rotation of the engine is Clock-Wise.

Clean the driveshaft to remove any debris or rust.  

I have found it best to install the upper pump housing on the shaft with the shaft while NOT in the lower unit.  The shaft simply slides into the splines in the lower gear.  The shaft can be put back in more easily after the impeller and upper housing are installed, than trying to fight the impeller and key position with no room to work against the lower impeller housing.  

Slide the water pump unit with impeller installed, down to near the flat on the shaft for the key, then place the key in the shaft’s flat, (chassis grease may help hold it).  The driveshaft has a flat in this location, but the key may be just a round pin.  Now move the pump housing down and rotate it to a location that the notch in the impeller and the flat on the driveshaft make it easy to install the key.  If you insist on a better key, a Mercury impeller key can be shortened to fit.  The Mercury keys are made in the form of a brimmed hat of extruded stainless.  They fit the flat better and have the rounded key made as an integral part.  These Mercury keys are usually are too long so need to be shortened slightly.

Align the drive shaft so the key is even with the bottom of the impeller.   Now you can slide the shaft and  upper housing/impeller down into the lower unit, engage the splines in the gear and install the four bolts on the top of the housing.  Once the pump housing is down and in place you can now replace the 4 bolts holding the housing to the lower unit. Remember the older pump housings require 2 longer bolts in the forward part as compared to the shorter 2 rear bolts.

Be sure that the rubber grommet on the rear of the pump housing is in place with the 2 rubber ears in the corresponding side holes of the housing.  These ears hold the grommet in place when you slide the copper tube into the grommet on final assembly.

You might consider placing a smear of Vaseline or chassis grease on the lower end  (where it mates into the grommet of the pump housing) of the copper tubing water tube leading up into the exhaust housing.  This grease helps insure this grommet does not get pushed out of position.

There is a large rubber O-Ring about 1 1/2" in diameter that sits on top of the water pump and between the exhaust housing, this ring more than likely will stay in the housing, however it may come off and be still on the upper pump housing.  It is essentially a seal and alignment between the water pump and the exhaust housing.  Check to see that it is still in place.  You might want to clean it up, apply a light coat of grease on it to ensure that it also aligns readily.

Driveshaft : Replace the rubber smaller O-Ring (5/8" OD x 3/32"width) on the driveshaft.  The driveshaft is made of stainless steel and is 1/2" dia.  The groove is placed so the O-ring rests against the bottom of the crankshaft, sealing grease in and water out of the splines, trying to eliminate the driveshaft from being stuck in the crankshaft extension.  This O-Ring goes in a groove around the upper splines about 7/8" down from the upper end on motors up until at least 1983.   This O-Ring does not show in the 1990 parts catalog.    This may have been eliminated as mentioned below due to the fact that some shafts broke at this groove.

If you forget to grease these upper splines, the next person to tear this motor apart 10 years from now may have trouble getting the shaft to separate from the motor.

In the photo below the upper drive shaft is the top end that goes into the crankshaft which shows 4 groove spline with the O-ring groove.  The lower shaft is smaller dia. (7/16") and shows the 10 groove splines of the same driveshaft that enter into the gearbox.

9.9/15 hp driveshaft ends.  Note the groove on the top end for the
O-Ring

The drive shaft has to reach from almost the centerline of the propeller shaft up into the crankshaft on the lowest part of the powerhead.  That's why if you are looking to buy a different or replacement shaft and are not sure of the overall length, you have to consider that they're longer than the transom to anti-ventilation plate as if you were measuring for "Short or Long" shaft motors.   You will notice the measurements below indicate a Plus or Minus 1/16".  This length will vary and since the shaft is captivated inside both the crankshaft and the lower unit driven gear, the shaft needs to be really a tad short as compared to being bound up and you not being able to tighten the lower unit to the midsection without it binding.

Short shaft actual Overall Length  22 3/8"  + - 1/16"
Long shaft actual Overall Length   27 3/8"  + - 1/16"
Extra Long shaft (Sail Master) actual Overall Length   32 3/8"  + - 1/16"

A stuck driveshaft in the crankshaft has been discussed above.

Broken or Twisted Driveshaft :  Yes, these props have a rubber hub as a shock absorber and no shear pin, BUT if you hit something with the prop that is pretty immovable when you are going fast, things can happen.  In the photos below you will be able to see what has happened, very unusual, but as seen here does happen occasionally.  In the LH photo, the upper end of the driveshaft broke in the recess for the O-Ring.

Here the upper  end of the driveshaft is twisted off & the broken off part was stuck in the crankshaft Here the lower end of the driveshaft that is in the gearbox is twisted at least 1/4 of a turn

Before you try to bolt it back together check to see the exhaust baffle is still in place, the stainless steel baffle screen that is slid into (supposed to be staked in) the rear divided section of the exhaust housing at the juncture where the gear case fits together.  It simply slides in a slot which is held in place when the exhaust housing and gear case unit are assembled.  If this is left out it may increase the noise level to some degree.

Shown here the baffle with lots of 1/4" holes

For a short shaft motor, align the driveshaft splines with the crankshaft and the shift linkage rod at about the same time.  Slide the complete gear case up to where the linkage rod is in the clamp.  You can look in  and see if the upper shifting shaft groove is in the proper location to go into the coupler hole.  If it won't align so the upper shifting shaft groove aligns with the upper threaded hole, you may have to jockey the position using a screwdriver tip forced into the vertical slot of the coupler while moving the shifting lever to FORWARD.  You might even have to use a small Phillips screwdriver or similar object that can be inserted into the threaded coupler hole to perfectly align the upper shaft to the upper coupler hole.  Once this aligned, you can then use a flexible pickup tool to insert the upper screw and get it started into the threads.  Now you can reach in with a large screwdriver and finish tightening this upper screw.  As a final precaution, use a 1/4" drive speed handle and a proper socket (3/8" to do the final tightening.  Do not forget the lock-washer under the screw head.

Then slide the lower unit in place with the water tube to the water pump and slide the lower unit up until it is tight with the midsection.  You might have to shift the lever into neutral or reverse to accomplish this.

For a long shaft motor, there is an extra rubber bushing about 4" long that goes into a cavity of the extension.  This has a hole in the middle that the water tube goes inside of and is automatically aligned with the water pump outlet.  HOWEVER, if someone has made the 3/8" water pump tube extension by just expanding 1/2" of one end, you will need to make a spacer (1/2" tubing about 3/4"long) to slide over it so that this tube bottoms out inside the above mentioned 4" rubber bushing.   You will need to do some measuring to insure that this extension tube will be secured inside the rubber bushing about 5/8" (or the same amount needed to match what is needed to fit inside the the water pump grommet) above the lower edge of the housing extension.

This is needed otherwise when installing onto the exhaust housing, which you can not see what is happening, this extension tube may well be pushed all the way into the water pump outlet grommet, bottoming out against the lower water pump plate & totally blocking any water from being forced up into the water tube.

Pull the shifter rod up into it's highest point (into reverse) from the lower unit.  Be sure you completely remove upper clamp screw from the coupler clamp.  You need to expand the coupler ever so slightly so it doesn't drag on the shift rod when reassembly and push the rod back down.  Once it is close, move the shift handle on the motor so is lines the groove up for the slotted screw to reattach the coupler.   You need to be able to see thru the screw hole & tell whether this location is in line with the groove in the upper shifting rod so you can put the screw back in place with minimal difficulty. 

You will have about 1/2" of space between the lower unit's upper edge & the lower part of the exhaust housing.  Place the upper clamp bolt in the clamp (it may help to use a spring fingered type pickup tool to hold it in the narrow slot between the units), tighten the screw.  With everything now in place on the exhaust housing, push the lower unit up, being sure the copper tube is still aligned and in the rubber grommet of the pump housing.  At this same time you need to have the driveshaft splines engage the motor’s crankshaft splines.  If it does not go readily, you may have to either rotate the flywheel or the prop, or both.  As everything slides together the shifting linkage will move the lower rod down to match the forward position of the shifting lever.  Once everything slides together, you can replace the 6 bolts holding the lower unit to the exhaust housing.

If you get it all back together and running, but you still get no water spraying out the overboard water indicator hole, quickly get your small wire, again poke it into the hole to try to break up any debris that may be lodged in the small overboard hole.

OK, Your Reassembled it & Now it Doesn't Pump Water :   This one can be a head scratcher.  Is the pee hole line plugged, however the block was getting hot?  Did I misplace the impeller key.  Did I forget the water pump lower impeller plate?  Did I get the water outlet line in the grommet wrong?  Is the water pump housing tightened down?   Is my test tank loaded with debris and are the intake screens plugged?   ???

All I can say is tear it apart again, (it now takes me 45 min to tear down and reassemble).  The one thing I double checked was the impeller inner hub may have become separated from the rubber impeller.  No, that was fine.  A new impeller sells for about $15.00. 

I had the above happen in a 1987, described above, that after a complete rebuild, and using the new impeller, it would run for 1 minute squirting water out the pee hole before the flow diminished and then steam started coming out.  I shut it down for a few minutes, started over, exactly a repeat of before, again for the 3rd and 4th times.  Took the thermostat out and some water comes out while running, but not as much as expected.  I tore it down the second time and still found nothing that I was sure was the problem. 

After reassembly and test running, the same problem existed as before, so another tear down was on the horizon.

This time however I found another used water pump housing that did not look much different than the one that was on the motor.  I steel wooled the stainless liner shiny, and replaced the then as new impeller.  But before I installed the lower unit, I fabricated the above shown water-jacket flush adapter and attached the plastic tube to the water supply tube to the motor and flushed it with a full force of the garden hose.  Water came out with force in every place that I would have expected it to.

Upon another re-assembly and placing the motor in the test tank this time it ran like it was supposed to.  I'm not really sure what I did, but maybe there was some sort of a blockage that floated around inside the block and at times would block the flow where the water pump was not powerful enough to dislodge it, OR the 3rd time maybe was a charm.  I am not complaining enough to investigate any further however.

Also some mechanics say that some aftermarket impellers are not made to specs and the small sealer ridges on the center rubber are not thick enough allowing water to be pushed back by.

Removal & Replacement of the Shaft Seals Without Disassembling the Lower Unit :   The prop shaft seals consist of 2 back to back seals of the same size.  This method uses one to keep the water out while the other keeps the oil in.  These two seals are identical, but are placed back to back.

To remove the prop shaft seals without tearing the whole lower unit apart, you can make or purchase a slide hammer puller that has a metal screw on the front end.  These can usually be purchased from automotive repair shops or Harbor Freight.  Screw the screw into the seal being careful to not gouge the housing or the shaft.  Tap the slide hammer handle a few times & the seal will usually start to move.  Once it is out, go back and do the same thing again on the inner seal. 

Once they are out, clean the cavity that they came from so the new seals can be forced in without any damage to them.

Replace these seals the same way they came off.  You will need some sort of a solid round object to drive the seals back in with.  Sometimes you can find a 1/2" drive deep socket or a cheap lawnmower spark plug socket that may be of the appropriate size to put pressure on the outer rim of the seal as you tap it in.

UPDATE  2012 --  The older 2 seal units have been replaced by a new factory dual lip, single seal #396350 as seen in the photo below.  This new seal still uses two seals, but they are built into this new seal assembly.  However you may still see the older back to back seals offered from the aftermarket parts trade.

Shown here is the new single prop shaft seal

Disassemble or Rebuild the Gearcase :  The lower unit, or gearcase needs to be taken off as if you were replacing the water pump impeller.  

Remove the (2),  1/4" screws that come in from the rear above and below the propshaft exhaust opening.  You may luck out and be able to rotate the bearing housing, then pull it rearward, then tap or pry it back.  However be careful not to break anything, so look at the next paragraph.

OMC makes a gearcase bearing housing puller #386631.  The puller pictured below is a actual copy that I made off the original OMC puller drawings.   You can make your own simpler puller by using (2), 5" pieces of 1/4" X 20 TPI, or course all-thread, (6) 1/4" nuts and (2) flat washers for the stand offs.  The puller cross bar needs to be 1/2" x 1 1/2" flat bar 5" long. In this cross bar drill (1) 1/2" hole in the center.  Then on each side of the 1/2" hole drill (1) 1/4" hole 1 5/8", so that these 1/4" holes are 3 1/4" apart with the 1/2" hole in the center of them.  Now screw (2) nuts onto the rod at about the middle and lock them down, one against the other.   These double nuts now give you something to use to screw the rods into the gearcase with.  Screw the other nuts, (1) on each rod in from the outermost end in about 1", and slide the flat washer on outside of the nut as added support when you assemble everything and then start your pulling.  

Gearcase bearing housing puller in use

In use, these rods are threaded into the existing 2 holes which the bearing housing is retained to the gearcase with, which act as a guide and stand-off when pulling.  Thread these rods into the existing holes and adjust the 2 end  nuts are about equal distance  to accommodate any length needed to set the crossbar in the appropriate position..  The crossbar slides over the rods on the outer ends of the rods.  The propshaft goes thru the crossbar's center 1/2" hole.  The prop nut is now reinstalled onto the shaft outside of the crossbar where it is used in conjunction with the other puller rods to pull the shaft, which in turn pulls the bearing housing out of the gearcase.  You may have to hold the propshaft with pliers to keep it from turning, being careful to not mar the splines when you tighten the prop nut to pull this unit.  

The bearing housing only has to move about 3/8" to come free.  It comes hard enough that you WILL PROBABLY need this puller to do the job. It will usually come hard for the first 1/8" or so, as there will usually be some debris around the inside of the housing around the large internal O-Ring that acts as a sealer between the bearing housing and the gearcase.

If the bearing housing is frozen into the gearcase, it will usually be at the rear as the housing slides into the gearcase about 1/2".   If the motor was used in saltwater and not flushed good, there may be salt corrosion between the 2 parts enough to seize them together.  If this is the situation you may be able to see where the gearcase has cracked in this area because of the corrosion (as seen in the photo below). 

There is a lot of internal pressure here from the corroding salty aluminum.  You can try penetrating oil, tapping the areas with a hammer, even trying some heat from a torch, but in my experience you are wasting your time.  If you do get it apart, the damage is not really reparable.  If so, many times you will not be able to pull the bearing housing out without ruining things.  If this is the case, it is suggested that you leave it alone, refill the gear oil, replace the drain pug seals and run it as is until you can purchase another better used gearcase assembly, and then try to salvage yours out for spare parts.  I have seen one so bad that the only way to get it apart was to cut it in numerous sections with a metal bandsaw.   It was so bad that no internal parts were salvageable.

Internal corrosion cracks at rear of housing
.

Unscrew the shift rod that is protruding upward in the front section of this unit.  It will unscrew about 3/8", then can be pulled upward and separated from the unit.  You now have to remove the #2 Philips headed screw from the RH outside of the lower case.  This is the pivot point for the internal shift linkage.

Disassemble & Inspect the Internal Gearcase Parts :  If you have any water in the gearbox, one thing to check is to see if the motor hit something hard while running and bent the propshaft.  Do this before you tear the gearbox apart as it may save you headaches later if the shaft is bent.  A quick check for this is to put a Phillips screwdriver tip (pointy end) in the centering hole on the back of the propshaft and while holding the screwdriver handle, with the motor in neutral, spin the prop and see if you feel any wobble.   It's not a super accurate test, but a quick one that anybody can easily perform.

Now you can disassemble all the internal parts, clean, wash them off in solvent, inspect for any damage.  There are (2),  7/32" steel balls with a spring between them that go thru  the propshaft that keeps the shifter (clutch dog) in place.  One thing to observe when taking the parts out is the condition of the old gear oil.  Check to see if it has any filings or metal flakes, gear teeth, which would be indicative of bad bearings or gear parts.  Lay the parts out in a sequence that you took them apart.  Your service or parts manual becomes invaluable here.  You may even want to use a digital camera to record where things came from.

Check the shifter (clutch dogs) to see if they are battered on one end.  There are 3 of these dogs on each side, which engage either the forward or reverse gear.  If the forward side leading edge has become battered slightly, (probably because of improper linkage adjustment) the shifter can be reversed on reassembly so that these battered dogs now engage on the reverse side.  This should have minimal problems as reverse is used way less than forward to neutral.

Shown here are the propshaft, bearing housing, gears, clutch dog, front Timken bearing & lower shifting rod attached to the shifter yoke.  It is missing the clutch dog slider in the center.

If there has been a water leakage into the gearcase and or it has sat unattended over a winter season or more, the bearings could be rusted which need replacing.  There are (3) Torrington needle bearings, (1) small thrust ball bearing and (1) Timken tapered bearing in this unit.  There are also (1), O-Ring seal around the shifting linkage, and (2) sets of double seals placed back to back on the driveshaft, also (2) on the propshaft.  These seals are priced at about $14.50 each with the O-ring at $1.00.  It may be advisable to replace them while you have the unit apart if there is any doubt of leakage, either in our out.

Exploded View of the lower Unit

The below part numbers & nomenclature was taken from a 1978 parts list which should be the same for all 1974 thru 1992
it is possible that some of these numbers could currently be superseded

  388001  GEARCASE ASSY, Less driveshaft & pump   35 319085  SEAL, Impeller housing
1 388276  BEARING HOUSING   36 301551  WASHER, Connector to shift rod
2 321481  SEAL, Bearing housing to prop shaft   37 302497  GROMMET, water tube lower
3 386125  BEARING, Reverse gear   38 388289  IMPELLER HOUSING & SEAL ASSY.
4 386231  BEARING   *39 318972  SEAL, Impeller housing to driveshaft
5 318877  CRADLE, Clutch dog   *40 386084  IMPELLER ASSEMBLY
6 304071  SCREW,  Bearing housing to gearcase   *41 300611  PIN, Impeller to driveshaft
7 308627  "O" RING, Bearing housing to gearcase   *42 318995  PLATE, Impeller housing
8 318861  GEAR, Reverse   43 321455  DRIVESHAFT, Standard
9 322097  PROPELLER SHAFT   44 552906  COTTER PIN, Prop nut to shaft
10 316505  SPRING, Detent   45 318971  NUT, Prop
11 316506  BALL, Detent   46 318959  THRUST WASHER, Prop shaft, rear
12 316501  SHIFTER, Clutch dog   47 318992  SHIFT ROD, Lower, standard length
13 388416  SHIFTER LEVER & YOKE ASSY.   48 304024  SCREW, Shift rod connector
14 308376  PIVOT PIN, Shifter lever   49 303794  CONNECTOR, Shift rod
15 386076  GEAR & BUSHING ASSY, Forward   *50 322087  CUP, Impeller housing
16 386186  ROLLER BEARING, Forward gear   51 386670  PROPELLER, 9 x 10"
17 322341  PINION, Driveshaft   51 387389  PROPELLER, 9 1/4 x 8"
18 322202  THRUST WASHER, Lower pinion gear   51 386118  PROPELLER, 9 1/2" x 10", Standard
19 388000  THRUST BEARING, Pinion   51 386669  PROPELLER, 10" x 5"
20 322201  THRUST WASHER, Upper pinion bearing   52 319484  CONVERGING RING
21 388002  GEARCASE, Bearing & seal assy   53 386119  PROPELLER BUSHING ASSY
22 388014  BEARING ASSY, Driveshaft   54 303067  "O" RING. Driveshaft
23 318874  SLEEVE, Bearing driveshaft   55 308744  SCREW, Gearcase to exhaust housing
24 321480  SEAL,  Gearcase to driveshaft   Below are parts for the 5" longer or "Long Shaft" versions
25 301877  "O" RING. Bushing to shift rod   43 321456  DRIVESHAFT, Long shaft
26 304765  BUSHING, Shift rod   47 319298  SHIFT ROD, Lower, long shaft
27 321738  WASHER, Seal shift rod   54 303067  "O" RING. Driveshaft to crankshaft
28 386071  BEARING ASSY, Pinion to gearcase   56 308744  SCREW, Extension
29 318991  SCREEN, Water intake   57 319340  EXTENSION, Impeller housing to exhaust housing
30 307551  PLUG & WASHER   58 320025  TUBE, Water
31 311598  WASHER   59 202893  "O" RING. Water tube extension
32 318966  THRUST BUSHING, prop   60 319314  EXTENSION,  5" Gearcase "Long Shaft"
*33 324334  SCREW, Impeller housing to gearcase, short   60 123023  EXTENSION,  10" Gearcase "Extra Long Shaft"
*34 324474  SCREW, Impeller housing to gearcase, long   61 389112  WATER PUMP REPAIR KIT
* Contents of water pump repair kit   62 389114  CHROME PUMP KIT

Removal & Replacement of the Shaft Seals When the Unit is Apart :   To remove the prop shaft seals, you can make a puller by using a 5/16" or 3/8" rod about 15" long.  Make a sharp bend on one end, that protrudes out about 3/8".  Grind both top and bottom of this protrusion so that there is a flat on the bottom and no radius on the inside.  Thread the other end long enough to accept a couple of nuts.  To remove the propshaft seals, screw a couple of nuts on the end, jam them tight so that no part of the threaded rod protrudes.  Lay the bearing (propshaft) housing on a flat surface with the rear surface down.  Insert your removal rod down inside the bearings and against the rear seals.  Pound down on the nuts with a hammer, removing the seals from this housing.  Another method would be to drive them out from behind using a 9/16 in long socket and a hammer with the bearing housing sitting vertically, outer side facing down.  Place the socket through the back and through the larger inner bearing.  Then hitting the smaller outer bearing, drive the bearing and the 2 seals out. 

You will notice that 2 these seals are installed back to back, this is a dual purpose, one is to seal the oil from escaping from the inside while the other is to seal the water out.  Replace them the same way they came off.  You will need some sort of a solid round object to drive the seals back in with.  Sometimes you can find a 1/2" drive socket that may be of the appropriate size to put pressure on the outer rim of the seal.

For the driveshaft seals, you can use the same removal rod as above, but inserting it from the top and by hooking the protrusion under the seals.  Install the slide hammer, again the nuts on the end.  With the slide hammer, pull these seals from the upper gearcase unit.  These might well be in rather solid, and you may have to resort to a Dremel tool and a cutter to remove some metal from the seals to relieve tension.  DO NOT cut so deep that you nick the gearcase, as this would allow water/oil leakage.  It seems to work best to tip the gearcase upside down in this instance while you are pounding downward.  Once they are out and things are cleaned up, replace the seals the same back to back installation as described above.  It should noted that care need to be taken to keep any residue out of the bearings.  This can be done to some extent by tamping a section of paper towel into the bearings, and removing it just prior to reassembly.

If you need to replace the needle bearings in either of the above units, do so before you replace the seals.  You will need a puller about the same as the one mentioned above to pull the bearings. And properly sized bearing cup bushings are needed to drive the bearings back into the housings

The lower shifting rod can become pitted at the O-Ring seal area.  If this is the case, either replace it, or since it is stainless steel, you can silver solder up the pitting, then lathe turn or bandsand it back down to close to the original size and polish it.  Is does no good to rebuild this unit, then allow a minor spot to be a leakage point.  To replace the O-Ring seal for this rod IF you are to totally disassemble the unit, you will need a slide hammer type puller.  Take a 1/4" All-Thread about 15" long, slightly taper one end, and grind off the corners of a 1/4" nut so that it will just go inside the hole (about .400" diameter)  in the lower unit that this shifting rod goes into.  Push the pointed end of All-Thread down thru the shifting rod hole in the gearcase housing.  Using a flexible spring loaded pick-up tools, position the ground off nut inside the gearcase housing and thread the All-Thread into this nut.   Make a bar of steel with a hole drilled in the middle or you can use a steering wheel puller laying it across the top as shown below in the right.  Just tighten the top nut, pulling the to pull the seal and bronze guide as a unit.

Improvised seal puller

Pulling the shifting rod seal with a commercial puller plate

Clean them up, and in all probability the lower steel washer used under the O-Ring seal on the older units may get deformed in this pulling operation.  Hammer it flat again.   The newer units use a nylon washer.   With this nylon washer, you may well ruin it by pulling the nut into it during the removal process.

Remove the old O-Ring from inside the brass guide, clean up the O-Ring recess, install the new one in the brass guide.  This O-Ring is a normal O-Ring that you may find in any well stocked plumbing supply store which has a 1/4" hole, 5/32" thick and 9/16" outside diameter.  Place the washer in the hole first and be sure it goes to the bottom of the hole and is sitting there flat, (not tipped).  Now with a fingered pickup tool place brass guide, O-Ring assembly down and started in the hole in the lower unit that they came from. 

Use a 1/2" rod to drive all these parts back down into the gearcase housing until they bottom out in the pocket.

Water Intake Screen : Another important thing to inspect is the water intake screen that is in this unit.  If the screens have been damaged, which can be observed from the outside, it should also be replaced, as if large intake holes are there, then debris can get sucked into the water pump and farther up into and possibly plug the internal water passages.  This is simply a small plastic basket that is tapered on 4 sides and has perforation holes on 2 sides which acts as a filter for larger debris.  The screen is inserted into a blind hole of the intake cavity.  The old screen is removed by simply using a long screwdriver to break it apart enough to remove the pieces.  The new one is inserted by making a wooden insertion tool the shape of the internal part of it then tapping it down into place.

Do not poke holes in from the outside, trying to clear any debris from the intake screen area as you will break the thin plastic screens.  Under the water pump deep in a pocket in the gear case unit is the water intake screen, it is simply a white tapered plastic box with some holes in it that is pushed down into a pocket behind the 5 intake holes to filter the intake water.   It is SCREEN, water intake, part #318991.   If you replace it, be careful as it is delicate and the hole it goes into needs to be cleaned pretty well or you will break the bottom out when you push it in.  You need to cut a wooden push stick that just fits inside the screen to support it as you push it into place.
 
Close-up of a water intake screen showing openings on both sides

Reassemble the Internal Gearcase Parts :   Once everything is ready, now you can start reassembling.  Put the Timken tapered bearing in it's race in the front of the housing first.  The manual calls for the use of a shifter yoke locator tool.  This is nothing more than a speedometer type cable or soft wire  about 20" long, with a short 10-24 size screw (same size threads as the shifter rod) silver soldered to to one end.  Some mechanics say you can get by without it, but experience indicates it's usage far outweighs the problems encountered without it.  In use the cable is fed down thru the shifter rod bushing and O-Ring unit, out the bottom rear of the gearcase enough to allow it to be screwed into the shifter yoke maybe 2 threads or so.  The forward bevel gear is positioned in place on the shifter yoke.  The clutch dog cradle should be snapped into place on the yoke arms, then these parts guided in this unit in from the rear and being guided by pulling on the cable, you can guide it into place.  This is a tight fit to get things down low enough, yet keep the lower shifter yoke aligned to go into the lower slot and at the same time pull the front end with the locator tool. 

Here is a shifter yoke locator tool made from a stranded size 10 electrical wire

Now you can install the pinion gear.  But to get it in place you need to slightly tip the forward gear down in front to allow enough clearance to get the pinion gear to be installed. The upper thrust washer, thrust bearing (not a real bearing, but a hardened washer like bearing), and lower thrust washer.  These 2 thrust washers are a different thickness. Place the thinner one onto the pinion gear first with the outer chamfer down, then the bearing and lastly the upper, thicker washer goes on it with the chamfer edge up.  You now need a approximate 5/16" dia. rod with a 1 1/2" 90 degree bend on one end, forming an Ell.  A 5/16" long shank Allen wrench will work.  On this assembly rod tool, you stack the pinion gear, bearing and washer unit, which you can now guide into the gearcase housing, up into the lower driveshaft bearing.

 Once everything is in place, you can now look thru the pivot hole in the outer RH side of the housing, by pulling the locator tool and using a long screwdriver, jockey the gear/yoke until the yoke hole aligns with the housing hole.  You might have to use a long pointed ice pick type tool to really align it once you get it close.  Then install the Philips headed pivot screw which you have installed a new seal under the head, into the gearcase and into the pivot hole of the yoke.

Next you will have to reinstall the lower shifter rod down thru the O-Ring seal and align it with the threaded end of the shifter yoke.  You might need the use of a flashlight and by slightly moving the yoke internally to get the yoke's threaded end to be in line to allow the shifter rod to be threaded into it.  Screw it in until it stops, and if the bend is not facing forward, back it up to where the bend does face forward.

Now, with the use of a spring fingered type mechanics pickup tool, you can position the clutch dog (which as a groove on each dog that goes forward) on the cradle, push it down, then rotate in into place with these 2 grooves pointing forward. 

Take the prop shaft, install the detent spring and apply some trailer wheel bearing grease on the outer ends of the spring and at the holes in the shaft.  Position the 2 ball detent ball bearings in this grease to hold them in place temporarily.  Slide the propshaft down into the gearcase taking care to align the ball bearings with the ears of the clutch dog, which has a slight taper at this location to allow both the springs to be compressed then slide inside the dog.  Be sure that both springs are encapsulated inside the slider dog.   Push the prop shaft in thru the forward gear and into the front bearing.   If the shaft does not want to go far enough down, then with the shifting rod, pull it out sliding the shifter dog rearward, allowing the ball to slide inside the dog.

Now the reverse gear can be slid onto the propshaft.  Be sure the rear bearing housing has been cleaned on the forward end and a new O-Ring installed.  Lightly oil the O-Ring and the propshaft.  This rear bearing housing can now be slid on the propshaft and aligned with the 2 rear holes then tightened up.  It may be advisable to place some anti-seize on the inner rear mating surfaces and the threads before reinstalling them so that disassembly is assured the next time someone tries to take it apart.

The driveshaft and water pump can now be installed on the gearcase housing and the whole unit then reinstalled on the motor's exhaust housing as described before in the water pump replacement section.

On your final reassembly when installing the prop, there needs to be a thrust washer (brass for early motors or nylon for later) between the rear of the prop and under the prop nut.  This thrust washer is about 1 1/8" OD and is splined to match the propshaft on the inside.  I have checked the 3 motors I have left from 74 to 92 one had prop forward/aft movement of just under 1/8" down to barely noticeable.  If you have considerably more forward/aft movement in the prop when it is installed, someone has left out the thrust washer.

Pressure Test the Gearcase :  If you are not rebuilding the gearcase, but suspect a leak, drain the unit, install either the drain/fill or the oil level screw, then apply 7 to 12# of air pressure with a Mity Mite, to the other remaining open oil screw hole.  That should allow you to find the actual source of the leakage either by sight, sound, or both if using soapy water so you can see the air bubbles if it is leaking.  

At that point, once you have identified the leak, it's a matter of replacing that seal, and whatever might be related to it if that related item should also be faulty.

Another bit of advise, even if you have rebuilt the whole lower unit and replaced all the seals, it is a good idea of doing the pressure test BEFORE you fill the gearbox with oil.  You may have nicked the shifting rod O-Ring or had the bottom washer fall out of the hole just before you put the brass guide and O-Ring down in place, so could be having a leak there.  If you refill the oil and have this seal faulty, gear oil will run out the hole discussed above that needs to be cleaned to allow water to drain out.   

I had the above happen to me once and I really did not want to tear the whole gearbox apart AGAIN.   What I did  was pull the lower unit off as if I was replacing the impeller.   Now I could see down inside and verified the oil was seeping out of the shift shaft O-Ring area.  I drained the gear oil, then saved it.  I unscrewed the shifting rod.  Next I used a 5/16" X 18 tap and tapped the brass O-Ring guide.  Before starting I smeared boat trailer bearing grease on the starting flutes of the tap to catch the chips and to keep them out of the gearbox.  I used a 1/4" square socket to attach to the tap and a speed handle to do the tapping.  After removing the tap, and the welded a 5/16" bolt onto the 1/4" all-thread I had used for the earlier mentioned puller and with the slide handle, easily pulled the brass guide out of the housing.

After replacing everything, the shifting rod had no problem aligning into the shifting yoke threads deep in the unit as the thread ends have a slight tapered point that allows it to easily start into the threads.

Replace the Gear Oil :   There are 2 types of gear oil available, (1) the old regular type oil and (2) the newer synthetic oil.  These motors have ran for years on the older type, but the new synthetic oils are a lot slipperier, giving a lot better lubrication.  The synthetic oils will a little higher priced, but you get what you pay for and the synthetics give a cooler running longer life for your motor.  The one way to tell the difference between the two if you are trying to refill a unit that is unknown as to what type of oil is in it, is that the regular oil is usually a honey colored while the synthetic is a greenish blue.  This will not hold true IF the oil has been there for some time and has turned black from usage.

In replacing this gear oil, it is a lot easier to use a special pump and adapter that is made for this operation which many times comes as a unit when you purchase the bottle of oil.  It is a push handle made into the cap of the oil bottle and operates a small pump in the bottle with a hose that has a threaded nozzle that screws into the drain hole of the lower gearcase unit.   Or there are plastic tubes of this oil that you can unscrew the small cap that reveals a pointed or even threads of sorts end.  These can be held tightly enough to allow you to squeeze the oil into the gearbox.

In operation, WITH THE MOTOR STANDING UPRIGHT, you remove the upper screwdriver slotted large plug (this is the vent and oil level plug).  Now remove the lower plug that is the same size as the upper, (DO NOT REMOVE THE PHILIPS HEADED SCREW LOCATED NEXT TO IT) The Philips headed screw is a pivot screw for the internal shifting linkage.  If you remove it, things can get hairy trying to align it back into the shifting yoke, as this is normally done while the gearbox is apart and you can see when you are positioning it.

DO NOT REMOVE THE PHILLIPS SCREW AT THE RED ARROW Here a lower unit is being filled

The manual says it takes 9 oz to refill an empty unit.  If you think you did not get this amount in before oil flowed out the top hole, you may be right.  What has probably happened is a air bubble formed in the upper cavity and pushed some oil out above it.  Usually you can let it set for a while and the air bubble will dissipate, allowing you to add more.  If when you try to put more in it may push out some oil above the air bubble.

Screw the proper threaded hose fitting into the bottom hole, pump the oil in until it starts to run out the top.  Replace the top plug.  In replacing this plug first, you are now creating just enough of a vacuum on the oil that will allow you to unscrew the oil hose and install this lower plug before a lot of oil runs out.

Reinstall the Gearcase onto Midsection :   Grease the splines on the driveshaft with boat trailer axle waterproof grease.  Some of the older drive shafts have a Neoprene O-Ring around the grooves to retain the grease. 

Slide the lower unit and driveshaft up into the exhaust housing, aligning the driveshaft spline into the crankshaft mating spline, by feel, if it does not slide in, rotate the flywheel as you push the lower unit up.  Once the driveshaft has entered the crankshaft splines, your next thing is to (by using a flashlight) align the water supply tube in the exhaust housing into the water pump grommet.  Now you can concentrate on connecting the shifting rods.

Before you go too far, one precaution here that may help someone at a later date would be to before you reassemble things is to run a 1/4" X 28 TPI National Fine tap into each of these holes cleaning up the threads.  Then when you reassemble the unit, place a dab of anti-seize compound on the threads.  This can make for easier disassembly later on to insure that the bolts to not get seized up in the motor parts that are underwater.

For a short shaft motor, you have to align the copper tube, the driveshaft splines with the crankshaft and the shift linkage rod at about the same time.   For a long shaft motor, there is an extra rubber bushing about 4" long that goes into a cavity of the extension.  This has a hole in the middle that the water tube goes inside of and is automatically aligned with the water pump outlet. 

Place the shift coupler on the lower shifting rod protruding from the gearcase, align the groove with the holes in the coupler and tighten it in place.   Pull the lower shifting rod UP placing the gearbox into reverse.

Slide the complete gear case up to where the upper linkage rod from the powerhead is in the clamp.  You may have to place the shifting lever into forward, (lowering it to better align into the coupler).  If the lower sifting rod wants to be pushed down, place a screwdriver blade under the coupler and force it up.  This gains you enough to get the bolt in the clamp. 

Be sure you completely remove upper clamp screw from the coupler clamp.   You can look in and see if the upper rod shaft groove is in the proper location of the upper hole as shown in the illustration below.  You need to be able to see thru the screw hole & tell whether this location is in line with the groove in the upper shifting rod so you can put the screw back in place with minimal difficulty.   If it does not want to slide into the coupler hole, take the coupler off & slightly spread it by inserting a screwdriver into the slot & spreading it.

Shift Connector Coupler Positioning

It is possible to tighten this coupler with either of the thru bolts NOT in the retainer groove.   If this happens, you may not be able get it in gear, or if it does it will not come out into neutral.  Plus you have probably stripped the bolt threads.  A new bolt is a stainless steel hex head bolt 1/4"-28 TPI  X 1/2" long.  You can cut your own screwdriver slot by hacksawing it in or using a Dremel tool cut-off stone.  Be sure you use the original lock washer or a regular lock washer under the bolt head when assembling.

Place the upper clamp bolt in the clamp (it may help to use a spring fingered type pickup tool to hold it to get between the narrow slot between the units) and tighten the screw.  With everything now in place on the exhaust housing, push the lower unit up, being sure the copper tube is still aligned and in the rubber grommet of the pump housing.  As everything slides together the shifting linkage will move the lower rod down to match the forward position of the shifting lever. 

Again as you slide the gearcase up to mate with the midsection you need to have the driveshaft splines engage the motor’s crankshaft splines.  If it does not go readily, you may have to either rotate the flywheel or the prop, or both. 

Once everything slides together, you can replace the 6 bolts holding the lower unit to the exhaust housing.

Lower Thrust Mounts Worn :  Here there are 3 squarish rubber mounts, one on each side that are called lateral mounts plus a front one that is the actual thrust mount.  The side mounts do not normally wear, but the center front one is the one that takes the pressure.  This one can get crushed and when it does it will allow you to get movement by pushing/pulling the lower unit forward or backwards.  The side mounts can be replaced by removing the 2 cross bolts in the mount brackets.  

Replacing the front mount is possible without dropping the lower unit IF you make a tapered wedge out of wood, and drive it between the pivot housing and the midsection.  The problem here is that the shifting rod goes thru the pivot housing and there is really not enough room to tweek it without help of the wedge.   With the 2 units held apart by the wedge, you may now be able to by using a large screwdriver to force the front thrust mount out of position.  The new one goes in a lot easier than the old one came out.

It is possible to place a rubber shim between the actual worn mount and the center post that it bears against as a temporary fix.   One that I found was crushed to the point where about 3/16" shim was required.

Shown here by the blue arrow is the front thrust mount, with the lateral rubber one in the center of the photo.   These rubber mounts have (2) 1/4" holes running forward and aft apparently to conform somewhat to the round housing it bears against in the front.   After time the rubber may loose it's elasticity and you may get about 1/8" to 3/16" excess movement here. 

The (2) 1/4"  holes above and below the actual arrow point are for the cross-bolts that retain the brackets.

Lower thrust mount shown A worn thrust mount on the left, with a new one on right

Worry About Draining Water Out in Freezing Weather :  Those who live in cold climates where the temperature stays down COLD much of the winter may be concerned as to whether how to do a winterization where there is no water left internally that may freeze and break metal parts of the motor.  Where I live it hardly ever gets that cold so do not even think about freezing, but for those who do, read the below.

However for winterization, it seems that if you ran the motor until the thermostat opened, then quickly took it out of the water if in barrel, the thermostat should be open long enough for any water in the upper block and head to bypass the open stat and pass out the exhaust area.

There is a small drain hole in the stainless steel water pump cup.  If the drain hole in the lower unit (about 1/8” hole front and above round gearcase boss) is open and water drains out for upwards to a minute after you take it out of a barrel, that drains all the water in the exhaust housing along with the upper lower unit housing above the gearbox.


If it is not open and the internal area is filled with debris blocking any trapped water, I mention how to clean this in a above section.

 Copyright © 2004 - 2014 LeeRoy Wisner  All Rights Reserved

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Originally started 11-2004, Last Updated 10-10-2014   ***
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