, Evinrude, OMC, outboard motor, outboard motor repair, 9.9, 15 hp, date/year of manufacture, water pump, carburetor, long shaft, 15 hp conversion, sailmaster

Maintaining Johnson
 6hp / 8hp Outboards

1984 - 1991 ,   (Information & Observations)   

The photo above on the left is a 1984 with the one on the right being a 1986 model.  

There seems to be a gap in production of the 6hp motors from 1979 until 1984.  However there was a 4.5 and 7.5hp made from 1980-1983 which utilized the newer exhaust housing/lower unit, and the twist throttle unit used the cable type with a kill button on the throttle end as found on the later models .   Essentially the 7.5hp 1980-1983 motor was utilized as the basis for newer 6 and 8hp motors.  So any information of these 6 and 8hp motors would generally apply to those 7.5hp motors.  Some of the early 1980-1983 4.5hp motors used internal fuel tanks and different rope starters.  And one known 1983 6hp Johnson made in Belgium that was actually a 7.5hp with a restrictor plate between carburetor and the manifold.  So it appears that you may encounter some hybrids in this 1980-1983 era.

In 1984 (at least in the US) they came back out with a 6hp and also upped the 7.5 to an 8hp.  Now somewhere in the mix, I have seen a 1983 8hp, which does not show on any of the lists, so possibly it was a LATE LATE 83, but with the 8hp parts of a 84.  The only difference was that it was painted all white as compared to the gray lower sections of all the known 84s .

1992 saw another major change in the 6 and 8hp motors with a completely different rope starter unit that mounted over the flywheel.

Also there was a 5hp in this series, which consisted of basically a 6hp.  I have not been able to identify exactly what made it a 5hp instead of the 6hp, unless it had a slightly smaller intake manifold diameter or was actually a 6hp but sold with a 5 decal to be politically correct in certain restricted areas.  However in all probability it may have just a slightly smaller main jet, cutting the amount of fuel burned, lowering the RPM

General Observances :  The factory did however retain the spindle spool starter system of the 66 -79 for these 1984-1991 models.  These newer models are not crowded under the cowling and have lots of room there.

The only difference in the 6 and 8hp of these years appears to be the carburetor, intake manifold, reed valve plate assembly and the front part of the block to accommodate the larger reed valve unit on the 87 and newer motors.  This being the case the I am not sure until I can tear both apart, but it may be that the carburetor will just have a larger main-jet.

They utilize the familiar angled cowling joint used by the 9.9/15hp motors of the same years.  The 1984 model that I have has the whole lower section including the cowling pan painted gray, with the top fiberglass cowling painted white.

There appears to be no provision for electric start on these motors.   However the later ones after 1988 were possible to have a 12volt charging system on them.  They came standard with the 15" shaft length, but could be had in a long 20" or even 25" extra long shaft for sailboats.

They do have the thermostat on the upper rear of the head, held in by 3 bolts which is readily accessible.

I personally like the gray bottom paint as it hides the scuff marks and oil you normally get on these motors that are used as a fishing motor.  They are not a show motor, but a working motor.

I also find that this series of motors are pretty well bullet-proof as most of the bugs that may have been encountered on the previous model have been eliminated, as like now using the cable throttle system, the electronic ignition works well and they were made before a lot of plastic was introduced in the manufacture of them (less prone to break).

These motors, like many series also underwent minor changes during their production, like carburetors and ignition.

In the photo below you will see the front view of a 1984 6hp Johnson.  Note the "Slow Speed Adjustment"  "Lean / Rich" knob at the center top of the front panel.  This knob is the carburetor idle adjustment knob.  Obviously the handle on the right operates the starter and the knob on the left is the choke.  The two pronged coupler on the lower right is the fuel line connector.  The knob at the lower left on the transom mount is for the tilt lock.

Here is the front view of a 1984 6hp

Year of Manufacture :  This is important in any repair, for obvious reasons.  Prior to 1979, Johnson used the last 2 digits of the year in the model number.   Here is a LINK to help you determine any of the Johnsons.  And here is the LINK for the Evinrudes.  For those of you readers outside of the United States, here is another LINK that may better help with your motors.

After 1979, OMC's manufacturing year code, which included Evinrude, is the word "INTRODUCES", with each letter equating to a number ie:  I=1, N=2, T=3, R=4, etc. as illustrated below.  As before, the last 3 letters are what you are looking for.  Then in this case, disregard the last one, as it pertains only to a model revision that only on specific cases may be revalent to a marine repairman if problems arise.  A code of  J10ELENA would equate to Johnson, 10hp, Electric start, Long 20" shaft, EN = 1992, and the A could be a model revision, so this motor would probably be made in the very first part of the year.  You may encounter a code of something similar to J10SELCTC. This would have been  Johnson, 10hp, SailMaster, Electric start, Extra Long shaft, 1983, and the C could be a model revision.  In this case with the SE in the model number, indicating a SailMaster, all the SailMasters would have all had the extra long 25" shaft.   For more detailed information on worldwide production, CLICK HERE

DATE CODE

I

N

T

R

O

D

U

C

E

S

YEAR

1

2

3

4

5

6

7

8

9

0

Using this code system, if the motor was sold as an Evinrude, then the first letter would have been an E instead of the J for Johnson.   Then you can encounter motors made in or for other countries, which will have some added letters as mentioned later in this article.

Sometimes the nameplate found on the LH side of the upper steering/clamping bracket can get removed.  If this happens, you can still usually tell which motor it is by looking at the 25 cent size soft plug in the upper rear RH side of the block.  The model & year are stamped in this soft plug also but probably only up to 1979.  It is interesting to also note that the 6 hp uses the same block as the 8hp, so you could see either hp with the same 6R78M numbers here as the 8hp has.   You may find that the plug numbers do not match any of the codes, as the factory changed things as time went on.

Exploded Parts Lists :  For a internet link to a marine parts seller CLICK HERE  that has exploded views as shown below in this article.    From this business, you can identify the numbered parts ad purchase parts online from them.

Flywheel :  To get to the electronic ignition which are under the flywheel, you will need to pull the flywheel off the tapered shaft of the crankshaft.  Removal of this nut needs a 3/4" wrench.  If it is so tight that you can not loosen it normally, then try to tap the wrench with a medium hammer to jar the nut loose initially.  If that does not work then you will have to resort to a air impact gun.

Most times if you just loosen the flywheel nut a few threads, (leaving it about even with the shaft end) then hold onto the flywheel by wrapping your arm around it and lift up enough to put a lot of strain on (almost holding the motor upright) then rap the nut HARD with a HEAVY brass mallet, the flywheel should pop off the crankshaft spline.  The reason for the brass hammer is so it does not damage the nut or shaft threads.  You could get by with a regular hammer if you are careful.  One hard rap is better than a dozen love taps.

If this does not pop the flywheel loose, then you will have to resort to a flywheel puller as shown in use below.  These usually have 4 slots milled in the top flange to accommodate the bolts to be threaded into corresponding threaded holes in the top of the flywheel.  Here we will be using only 3 that are spaced evenly.  This puller could be also use if only 2 opposing holes were there.  The large bolt in top is threaded into the puller boss.  In use you thread the 3 smaller bolts into the flywheel so that they will allow the puller to set evenly on top.  You then tighten the large bolt into the puller, which puts pressure on the crankshaft end, pulling the flywheel up.  If it comes really tight, then with the large bolt's pressure on the crankshaft, rap the large bolt head with a hammer, which usually will help and pop it off.

Home made flywheel puller in position on a 6 or 8hp


This flywheel is located in the proper position on the crankshaft by a 1/2 round woodruff key.  This proper position is critical as to the timing when the CDI ignition spark fires the spark plugs.   If this key gets damaged or partly sheared, the motor will not run well, if even start.

Electronics :  And these newer motors used the newer Capacitor Discharge Ignition (CDI) system that uses a power pack as shown in the photo below on the left.  On the RH photo are shown the spark plugs, individual coils and the throttle cable attachment to the timing plate. 

6 / 8hp powerhead viewed from LH side 6 / 8hp powerhead viewed from RH side

 

Timing plate with electronic coil & pickup sensor for a prior to 1989 motor  
 

From observing the parts list, these motors from 1989 came set up with a UFI (Under Flywheel Ignition) eliminating the external power-pack.  They also had a AC or DC electrical outlet.  The AC would have been for sale in Europe, while the 12 volt DC by being run thru a regular rectifier for battery charging in the US.  There however was no provisions for a electric starter.

Spark Plugs :  Spark plugs for these motors need to be 14mm threads with a 1/2" reach.  They REQUIRE this thread length at 1/2".    By this the 1/2" reach is measured from the base of the threads to the end of the electrode and you will probably only have 3/8" of threads.  They will have a 13/16"hex body.   The plugs recommended here will fit the right "reach" length.    If you try to put anything longer in, they will reach too far and possibly hit the top of the piston. 

Most of the OMC models, at least from 1983 will have the tape in the spark plug wire recommending Champion L77J4 plug which would be the  corresponding conventional single electrode Champion plug.   You now may have to use  L77JC4,  or it's newer replacement #821 or the #821M for marine use.  If you can't get the "M" series, don't worry, as it is probably  just the outer metal coating that may be more resistant to salt air.  If you are using the motor to run to the fishing area and stop to fish or troll slowly for extended periods of time, these plugs are probably the better choice as they tend to not foul as bad as the air gap plugs do.   So, use the above information as to your usage to determine the plug you need, NOT necessarily the recommended one on the motor.

You may find a recommended plug of  Q
L77J4, this is the same plug as above but with a resistor or sometimes called a radio noise suppressor plug.  this one would be recommended of you are running a sonar/depthfinder or VHF radio.

Fuel Pump :  These fuel pumps are pretty universal, the same small square one fitting most all these small motors up to 40 hp until about 1987.  Since these motors used only a rope starter, the standard fuel pumps would be the small square version up until the 1987 transition.  For a link to the rebuild procedure for this older small square fuel pump  CLICK HERE.  For a link to the later larger fuel pump that came into being about mid 1987   CLICK HERE.  Now to throw a bit of confusion into the mix, the 1987 factory parts lists show "early" fuel pumps and "late" fuel pumps.  It appears that this "late style" was ONLY used the last part of 1987, as the parts list show ONLY the "early" small square pumps used after that year for this series of motors.

If you suspect a fuel problem, you can check the fuel pump by being able to suck, but not blow into the outlet, blow but not suck out of the inlet.

For you owners of 1987 motors, you will have to look at your own individual fuel pump to decide which it is, as I do not have data relating to serial numbers and collation of which was used during the transition era.

These motors use the single fuel line and the standard OMC quick fuel line couplers.

Carburetor :  For those of you unfamiliar with small outboard motor repair, to remove this carburetor, unscrew the three top bolts holding down the top plastic silencer/breather cover (29) in the illustration below.   The "Rich/Lean" idle knob can be pulled straight forward and off it's splined shaft.   Make a mental picture of which way the indicator  pointer is pointing so you can re-install it the same. 

Then unscrew the retainer screw holding on the choke knob (outside front of panel) and remove this knob.   The rear of this plastic choke rod connects to the carburetor choke arm by a small headed pin.  On some motors you may find the pin's head either on the outside of the connector or inside.   Remove this unthreaded pin.  Now you can withdraw the choke rod rearward and through it's hole in the lower plastic body (#28).   From there, the lower breather body can be lifted up and away from the carburetor.

There should also be a foam rubber seal (#26) that may be sticking the breather to the carburetor, if so, a bit of wriggling of the breather body should dislodge it.

The carburetor itself is held onto the intake manifold by two 1/4" SAE nuts, one on each side (#33)  (which uses a 7/16" wrench).

The carburetors used on these motors varied with the year of manufacture.  The early metal top ones (1984-1985 are rather simple units and quite reliable with a fixed main jet, otherwise called the "High Speed Orifice Plug" #24.  The hole size for the 6hp is #35 and for the 8hp is #36.  These numbers relate to drill bit sizes.   These early models have a metal bottom float bowl, while the later ones can have a plastic bowl.

The slow speed idle jet screw (#15 in the illustration below) has many small spline serrations on the outer end that mate with splines in the hard rubber knob.  The placement of this knob on the front cowling makes for only 180 degrees of rotation.  In doing any fine adjustments after final assembly on the motor, if you can not get the knob to rotate as far one way or the other to get a smooth idle, pull the knob straight forward and off the shaft, rotate it 180 degrees so you get a better chance to tune the motor.   Then once I get this "sweet spot", I like to pull it off again and position the pointer on the knob straight down, this gives me s then known return position and about 90 degrees of movement either way if my fuel ratio changes.

The normal number of turns out from lightly bottomed out for the low speed (idle jet) #15 is 1 1/2 turns as a start setting.  My motor likes 1 1/4 turns out.

 

Shown below is the carburetor & breather for a 1984 & 1985

 

1985  metal top carburetor with butterfly choke & metal fuel bowl

The later carburetors used a plastic top.  The early with these plastic tops still utilized the front mounted idle mixture screw.  Then about 1988 or so this screw hole was plugged and a rear starboard side adjustment screw was used.  These plastic topped ones used a internal box like collector that the main-jet was screwed into.  This system appears to help by separating to some degree any small debris from being sucked into the main-jet.  

The late intermediate style plastic top carburetor with side idle adjustment.  These also used a plastic bottom fuel bowl. 


Note in the photo below that the idle adjustment screw is moved to the rear side and the front hole is plugged plus that it has no choke as it uses the fuel primer system as indicated by the lower fuel line fitting which is the inlet for a choke/fuel primer as mentioned below.

Here is a 1989 8hp carburetor

To remove the carburetor from these motors, you will need to remove the breather box cover (3 screws)  then 2 more screws that hold the bottom of the box to the top of the carburetor.  Also the choke rod needs to be removed.  This is accomplished by first removing the small Neoprene O-Ring that acts as a retainer on the outer end of the choke retainer pin.  Pull the pin and then push the rod in and remove it from the rear of the front panel.

Also the starter spool will have to be partially removed.  Remove the 2 upper bolts, and carefully lift the spool out of it's base.  Tip it forward to give clearance for the 7/16" open end wrench to access the RH facing rear carburetor retainer nut.   Remove the carb cam roller pivot screw.  When both nuts are removed, you can pull the carburetor forward and then remove the inlet fuel line.

You can then remove the  bottom bowl, the float pivot shaft and lift off the float assembly which includes the inlet needle.  Place all parts so you can easily identify them for reassembly.  You can then unscrew the brass main jet and or idle jets.  If you have the older metal topped carburetor, it may be best not to even try to remove the slotted inner brass idle tube.

On my 1984 6hp the inner (rear) carburetor throat diameter is .810"  with the mating hole in the intake manifold being only .612".  This hole in the manifold is not cast but machined not true with the carburetor's mating hole, but slightly lower by about 1/8" or the top of the hole even with the top of the carb mounting studs.  Possibly one difference in the 8hp is this manifold diameter is larger.

In re-assembling any carburetor, IF it has a metal tag under one of the bowl screws, remember to put this back as the numbers on this tag may be critical if you ever need a repair kit.

Air breather or air box as they are usually called by the manufacturer on this motor is rather unique in that this motor appears to be somewhat semi-super charged.  By this, I mean the actual breather intake is mounted very close to the flywheel ring gear starter teeth.  In operation the rotation of the flywheel forces air from these teeth into the carburetor air box.

On these plastic topped carburetors, there is a slow speed stop adjustment screw (#31 in the illustration above) on the port side about the middle.  This just screw just adjusts the throttle shaft butterfly as a low speed setting.  It does not fine tune the idle jet (#15 in the illustration above) which is either on the center front of the plastic top or on the rear starboard side (depending on the year of manufacture).  You may have to adjust each individually, but in synchronization to get a good low trolling speed.

Choke / Fuel Primer :  These motors used 2 types of choking systems.  The 1984 and 1985 used the conventional butterfly choke.  1986 thru 1989 used a combo choke/fuel primer system.   They reverted back to the conventional choke system in 1990, WHY ?   A guess is that when these primer chokes work, everything is fine, but as they age, weird things start happening.   Actually it was not a choke as we know it, but merely a system that injects a small amount of fuel directly into the carburetor throat.

This primer system used a knob similar to and in the same location as the butterfly choke knob but in use, this choke knob is actually a dual function choke and primer system.  As you pull the knob all the way out it is injecting fuel into the intake (it's like a syringe and you can feel the tension as it's squirting the fuel into the carburetor) this is the primer function.   When you release the knob it should go back a little over 1/2 of the way in by it's self with the red ring at the base of the shaft still being visible, this is the choke position.  After the motor has warmed up a bit, you have to push the knob in all the way (it snaps in), this is the running position.

Fuel Primer unit exploded view diagram Fuel Primer symbol decal on front of cowling


If your motor has this fuel primer system and you are having problems where it seems that your motor is starving for fuel, or runs better with the breather off, and you are beating your head against the wall trying to figure out what is wrong, look at this type a primer unit.   There is a possibility that if the internal O-Rings are worn AND/OR the plunger is not fully retracted, you may be getting a air leak into the fuel system.   Or it may not be seating when pushed back in, thereby could be allowing extra fuel into the carburetor, flooding it out. 

Recommended Fuel / Oil Mix :   The formula shown below will be on all modern 2 cycle oil sold in the last 30 years or so.  On most all of the pints and quart plastic bottles of TWC-3 oils there will be a narrow clear vertical window on the edge of the bottles.  On the sides of this window will have numbers representing Ounces and Milliliters for other parts of the world.  Or you can purchase special measuring containers showing different ratios and the amount of ounces needed.

If your motor is to where you have to mix the oil, you need to know how much gasoline you will be needing, add the oil before you fill the fuel tank so that the oil mixes better that just dumping it in after you fuel up.  However if that is not possible, guess, then add a majority of what you think it will take, fuel up and then add the rest matching the amount of gasoline you took on.  If you are using portable fuel thanks, before hand, when you fill it, add 1 gallon at a time, use a clean 3/8" or 1/2" dowel, mark the dowel at each gallon and use it as a measuring stick.  This way you can refill a partly full tank with the known amount of oil.

A quart has 32 ounces of oil in it.  So for a portable 3 gallon tank normally used on these smaller motors, to fill it using the 50:1 ratio would take 8 ounces, (1/2 pint) or 1/4 of the quart.

FUEL MIXING TABLE

Gallons of Gasoline

Gasoline to Oil Ratio

Ounces of Oil to be Added

16:1 24:1 32:1 50:1 100:1
1 8 5 4 3 2
2 16 11 8 5 3
3 24 16 12 8 4
4 32 21 16 11 6
5 40 27 20 13 7
6 48 32 24 16 8

The official OMC fuel/oil mix for most outboard motors in this year ranges has for years been 50:1.  This means 50 parts of regular gasoline to 1 part of outboard motor oil.  Remember that this was before unleaded gasoline or even possibly an octane rating that was listed at the pumps.  Now the recommended fuel is 87 octane gasoline.   Or before the outboard industry came up with any TWC oil, much less the latest which is TWC-3 outboard motor oil. You probably will not see much of the older TWC-2 oil out there anymore.  You can spend your money and purchase OMC oil for about $6.50 a quart, or buy a name brand quart for $2.79. Sure the manufacturers want you to buy their oil, and for a new motor under warranty, it may be advisable to do so.  But the consensus from many experienced boaters is to use any good brand of oil, as long as it has the TWC-3 rating, it meets or exceeds the manufacturers specifications.  The TWC-3 represents, Two cycle, Water Cooled, type 3 formula.  The formula 3 has decarbonizing additives designed to be more compatible with the newer non-leaded fuel.

So from the above information, you can see that fuel and oils have changed dramatically since these motors were first brought out in 1974.  In this instance, times have changed for the good, as we now have a better gasoline and way better outboard oils.

Fuel/oil mix on all the OMC motors that have needle roller bearings is 50-1 of TCW-3 standard outboard oil.  However I have found that since I troll much of the time, other than getting there and back, I like to use a mix of 75-1 but of a SYNTHETIC blend oil instead of the standard oil.  This gives me at least the same or better motor lubrication, plus it gives me less smoke at a troll and the spark plugs last longer before fouling.

Recoil Starter :  The recoil starter uses a rope type spool system that works very much like an automotive type starter unit only manually.  
 

Port side view of the spool type starter on a 1984

To replace the rope, you should first remove the spark plug wires for safety.   The following was taken from a 1971 service manual but this later motor appears to use the same starter unit.  (1) Pull the rope out as far as you can, then allow it to retract less than one revolution until the rope end of the spool faces the port side of the motor.  Lock the starter in this position by lifting the starter pinion gear upward to engage the flywheel ring gear, then slide the slightly spread  handles of a pair of pliers under the gear, holding the gear upwards and into the flywheel gears.  (2)  remove the starter rope handle.  (3)  remove the rope from the spool.  (4)  Replace with a new rope, which needs to be 56 1/4" long, & burn the ends with match for about 1/2" to keep them from unraveling and to be stiff so they will hold in the spool or anchor.  Thread the rope thru the slot in the spool as it came out of.  (5)  Thread the rope thru the motor cover then install the handle.  (6)  Hold the starter rope handle to keep it from rewinding too rapidly, remove the pliers then allow the rope to rewind normally.  

To remove the starter unit from the power head, (1) pull the starter handle and form a knot in the rope to prevent the rope to recoil while removing the handle.  Remove the handle.  (2)  remove the rope.  Hold the starter spool and slowly allow the starter main spring to unwind completely.  Remove both the bearing head screws along with the front spring retainer plate screw, allowing the plate to drop enough to release the starter spring.  Lift the starter unit up and away from the powerhead.  (3) remove everything, clean and inspect for wear.

To reassemble the cleaned starter unit, (1) place the upper bushing and starter head with the pinion gear spring onto the spool. (2)  Insert the spring retainer in the spool.  Align the slot in the gear with holes in the spool and spring retainer.  Insert the roll pin with its split seam in a horizontal position to avoid dragging against the slot in the pinion gear.  (3) DO NOT oil the gear or spool, this will attract dirt, causing pinion to bind on spool.  (4)  Insert the spring into the bottom of the spool, turn to engage with the slot of the spring retainer.

To replace the starter unit to the powerhead,  (1) Place the bushing in the spring retainer plate.  (2) Twist the spring to lock the inner spring onto the spring carrier.  Pull the end of the outer spring out of the spool and hook it onto the retainer.  (3)  Place the guide in the starter plate.  Insert the spring hook into the retainer plate slot. (NOTE if the spring hook has broken off, you can re-bend the end).  Raise the retainer plate to hold the spring.  Install the front retainer plate screw and tighten the rear screw.  remove the spring from the spring retainer.  Install the starter assembly to the intake manifold. (4)  Place a heavy duty screwdriver or a brace with a screwdriver bit in the slot in the top of the starter spool shaft. Wind the main spring 16 1/2 turns counterclockwise.   Rope anchor hole in the spool should face to the port side of the powerhead.  Raise the pinion gear to engage the flywheel and lock it in position with pliers.  (5)  Install the rope as described in the rope replacement paragraph.

Exploded view of the 6 / 8 hp starter unit.

Upon re-assembly where you bolt down the upper housing plate #12, the rope guide #14 rests in a shallow hole in this upper plate.  It has to go into the hole as you tighten the 2 attachment bolts, otherwise you may break this plastic plate.  At the same time the plate has to go under the flywheel with minimal clearance.  You can not really see the hole, so this may take a bit of trial and error.

Reed Valves : These are a pretty simple and proven design.   This plate mounts between the intake manifold and the block.  In the photo below, the brass Vees are not the reeds themselves, but stoppers so the reeds do not get over bent and then break off.   Also in the photo below you see 2 reeds per side for the 6hp and the early 8hp models.  The later 8hp used basically the same but it has 3 reeds per side from 1988 on until the end of this series.

Reed valve plate for a 6hp & 8hp  from 1984 to 1987


Cable Type Throttle Linkage : 
These 6 and 8 hp motors 1984 and later, used a push/pull cable throttle linkage system.   The motor side of this throttle cable goes from the mounting bracket on the port side (LH facing forward) into the lower pan and up under the carburetor, around the opposite side and up to the rear top of the block and thermostat housing.  At the thermostat housing, the end of the outer cable has a threaded end into an female threaded plastic body that is attached to the thermostat housing by a bolt.  Adjustment in the throttle positioning is accomplished by unbolting and screwing the outer plastic either in or out if you want to readjust the indicator pointer to the speed letters.

 

If this twist handle seems hard to twist or to not want to move, the cable may be dry and binding inside, or the timing plate may also be dry and dragging.  To test this, removing the end of the cable at the timing plate, now see if the handle will now twist.  If not, then the problem is in the cable.  You may be able to remove the cable, then get some penetrating oil in to lubricate it.
 

To disassemble this handle unit, you will notice two small round holes 180 degrees from each other top and on the bottom.  You need to use a couple of punches, depress both of these at the same time, while pulling the handle off front-wise.  A helper can be useful in this instance.  Inside this plastic is a dual rotating cam slot which a cross-pin enters into spacers and rollers which is in turn attached into the cable end.  When disassembling these be careful to not loose this pin. 

 

After much usage the embossed Slow-Start-Fast indicators may get worn, however usually the start position is on top.  The start raised rib on the twist handle is usually aligned with what may have been the Start position on the handle.   When twisting the handle, the cable moves in or out. 

 

The photo below shows a 1984 with a multi -function idle/kill button on the end of the twist knob.  Inside the outer rotating knob, which is a low speed idle adjustment, is also a push button kill button.

 

To disassemble, push in on the 2 plungers simultaneously  (top & bottom) & pull the twist handle forward.  This reveals the slider cams which engage a cross-pin which activates the in/out cable movement. 

 

In the photo below you will see the black plastic threaded outer cable attachment bolt on the thermostat housing and the pivot bolt at the end of the inner cable/ timing plate arm.

You will also see a spare prop shear pin electrical taped to the plastic outer cable end.

Here the rear end of the throttle cable is secured on top of the thermostat housing with the inner end secured at the pivot bolt.  

 
Midsection &
Trim  / Tilt :
 There is a black knob, located close to the transom clamps of engine.  When put in one position, it locks the motor to the cross shaft, effectively locking it in that position, when the knob is turned to the opposite position, it allows the motor to freely tilt up or down.  It has a sketch of a boat with the motor raised on one side of this flat knob indicating it can be raised.

This lock needs to be in the lock position if you use the reverse gear on the motor so it won't kick up.  However, if you plan on using the motor for trolling in the shallows where you could drag the skeg, leave it unlocked.  Or use the shallow water drive latch located on the starboard side of the lower transom bracket.  

There is a fold out carrying handle tucked into the front of the clamping bracket.  The clamp screws are 5/8" diameter.

The twist grip throttle is activated by by a cable system that has a slow speed adjustment knob and a kill button on the outer end.

The upper and lower motor mounts are made of rubber and are the same part.  They appear to be very durable, plus easy to get to.

Midsection  exploded view


Muffler :  These motors have a small plastic cover that covers the upper exhaust vent on the rear of the midsection (#80 in the above illustration).  This does muffle the motor some, but in reality it was called a "water outlet" on the earlier models.  This muffler/outlet allows for some outlet water to mix with the exhaust gasses to cool the housing and at the same time allows only a small amount of exhaust with some spitting water, as an indicator of sorts, some may call it second exhaust port, however in actuality, in these smaller engines you could say it is an idle bypass, because at idle speeds there is not enough exhaust pressure to overcome the under-water pressure out the larger hole near the prop.

 So if you see a slight amount of blackish oil coming out of the bottom of this, it is normal.

Water Indicator :  These motors have the tell tale water indicator system common with most of the later motors.  These seem to be a bit more trouble free as related to plugging up as the outlet hose to the overboard tell tale takes off the side-plate cover near the top instead of the bottom.  This helps a bit in that it is less susceptible there to less debris plugging this tube.

Water Intake : These motors main water supply to the water pump comes from a screened tube right behind the prop in the exhaust outlet which was carried over from earlier motors.  Water is forced into the screened intake to the water pump by the prop thrust.  Some users report that when running these motors in a barrel, (usually a small one) that the prop has to be installed and usually in gear as apparently they need to get more water pushed to the water pump by the prop to get enough to cool when running  at over an idle.

There is no stainless steel intake plate on the left side above the cavitation plate like the previous versions.   Aftermarket flush kits for this motor are obsolete and rather scarce.  There is really no provision currently available for a easy muff system to run this motor out of a tank.  But there is hope.  I think that I may be able, (by tearing mine down) to figure out a way to drill/tap/modify the lower unit near the water pump to where I may be able to utilize the later screw in flush adapters on this motor.  But that is a project in itself.

Overheat Problems at Troll or in Tank :   If you happen to have the motor overheating at slow speeds, you might consider looking at the water intake screen tube which is situated in the lower unit directly behind the prop.  This is placed here so that the prop thrust pushes fresh water into this slotted screen tube.   This slotted screen could be inadvertently blocked enough that these holes could partially block water intake at a slow speed.

This slotted screen is made of plastic which would be hard to remove and save after many years, plus it is expensive to replace.  So using a small nail or similar tool, you should be able to carefully clean any debris from the holes clear enough to make a difference

When using this motor in a tank, always run it in forward gear as the water pickup tube is directly behind the prop, with the idea the prop will help push water into the pickup tube.  If the tube is partly plugged and the motor is ran mostly in neutral, the motor may not be getting enough cooling water and overheat.

Water  Pump/Impeller :  These motors utilize a different shifting system.  To disassemble this for water pump impeller replacement, there is a difference in the shifting rod from any previous motor of this size.  It rotates instead of moving vertically as seen by the #10 & #78 bevel gears (located under the carburetor) shown in the midsection exploded views below .  The upper end of the lower unit shifting rod is machined to match the #78 bevel gear coupler, which should just slide out and down when you drop the lower unit.  The whole shifting rod then drops down and then out the bottom with the lower unit.  This is a lot simpler to disassemble than the previous years.

Replacing it back into the midsection housing and re-aligning it after replacing the impeller may prove interesting.  This CAN all happen without having to remove the powerhead, however it may take a bit of jiggling to get things to slide back together.  The first part to align is the water tube, which slides into the long upper snout of the housing.  This snout is considerably longer than most, so it helps get the tube started while you can still see inside the midsection from below using  a flashlight.  The tube's lower end is cut on a angle to help facilitate easy entry into the grommet in the upper end of the snout.

Second the driveshaft and finally the shifting rod.  Initially I was worried about the shifting rod's re-alignment, but that was easy.  The hard part was to align the driveshaft.  It took a lot of eyeballing for the lower unit's upper mating surface to be even with the midsection's lower mating surface.  After the driveshaft slid into the splines by slightly rotating the flywheel as you push up, the lower unit slid up to within about 3/8" then it went into the shifting rod gear easily.  You can not see the shifting rod as it goes up inside it's own pocket, but it must have a internal tapered area at the top because things just slide in fine.

OMC  / Bombardier #0389576 water pump impeller $18.00    This impeller fits Evinrude and Johnson 4hp, 1980-1992; 4.5hp & 7.5hp, 1980-1983; 5hp, 1996-2005; 6hp, and 8hp from 1984 to 2005 2 stroke engines. 

Water pump impeller #0389576 Water pump kit

Now for a confusing part.  Since we are dealing with a used motor with no known repair history, we are not sure what had been previously done.  I purchased the proper identified impeller from the parts manual  #0389576.  Upon removal of the water pump, I found the existing impeller was the right diameter but thinner in vertical dimensions.  The recommended replacement was .845" thick while the existing one in this motor was .700" thick.  As luck would have it the existing one appears to have recently been replaced, so I just reinstalled it.

The experts say to not reuse a lower water pump plate if it is scored.  Well this one had a couple of deep circular partial grooves in it.  I disregarded the smaller diameter one near where the seal ridge of the impeller rubbed.  But there was one larger wear groove out farther and near the outer edge.  Not wanting to wait for a replacement, I took it to my band-sander and using a worn 240 grit belt, sanded this stainless steel plate from all directions to removed minute metal as evenly as possible.  OH yes, you will need to dip into water after each sanding, as it gets HOT. 

Thinning this plate should not have any effect on reliability as long as it was smooth, and this plate uses a gasket both on top and bottom, and the pump housing bolts on top.  Maybe not recommended, but it worked.

The stainless steel cup looked in better condition so nothing was needed on it.

Lower Unit :  They have a unitized gearcase accessible from the rear instead of the previous gearcase that split horizontally at the prop shaft line.  The prop is driven on by a stainless steel shear pin 3/16"dia. X  1 1/4" long.  There is a prop shaft nose cap on the rear that is retained by a cotter pin.

The new rotating shifting shaft cam in the lower unit, pushes a internal spring loaded rod that is in contact with the shifting clutch dog.

Remember that when you check/change gear oil, it is recommended to replace the drain plug plastic washer (#0311598) as they seem to be the most likely point of a leak.

The water intake is in the exhaust tube right behind the prop as used in the older smaller OMC engines as seen by the screen #24 hanging down in the exploded drawing below.   And it offers no real opportunity to attach a currently made flushing attachment. 

One thing they made provisions for was a recessed location in the lower unit to install a zinc anode, #47 in the exploded views below.

One thing I may warn you is that when you try to reinstall the lower drain/fill plug, is that IF the plastic washer remains in the hole, you may very easily NOT be able to start the threads straight.  And this threaded hole sets at a slight angle with the outer housing when it is tightened in tight.  If it looks like it is going in crooked, stop before you ruin what threads are left.  If the unit is full of oil, you may be able to lay it down enough to be able to remove the plug without a lot of oil draining out.   A 3/8" X 16 NC tap can be ran in VERY CAREFULLY to clean up the slightly cross-threaded threads.  AGAIN, VERY CAREFULLY.

Here the lower unit is in exploded view for a 1984, with the long & extra long shaft spacers are on the upper left

To remove the lower unit on these motors there is one bolt in front that is quite visible (#5 for a short or extra long shaft, or #58 for a long shaft in the illustration above).  There are also two more bolts underneath, above the prop (#56).  Removing all three of these should allow the lower unit to be withdrawn from the exhaust housing and down to where you can remove it to access the water pump housing (#24).

If this does not allow the lower unit to drop down, possibly some previous mechanic did not grease the upper driveshaft splines and it is stuck in the crankshaft.  If this is the case, wooden wedges driven equally around the midsection/lower unit may be your alternative.

Propeller
 The prop is a NON THRU THE HUB type.  The prop has a shear pin and the plastic bullet nose is just a retainer that is held in place by the cotter-pin.  These props have a rubber hub bonded to the prop along with to the bronze hub.   On my prop the rubber must have gotten some corrosion between the prop and the inner hub, forcing the hub forward about 1/16".  This made it very hard to get the shear pin in place while still having the brass spacer #54 shown above.  I tried to press the hub rearward, but no avail as the rubber was still bonded (or stuck), so I simply chucked the prop in the lathe and removed that amount off the rear of the prop to allow the spacer to be in place and to accept the cotter pin #53.  

The prop shaft is .531 or 17/32".  why this odd dia. ?  Well my guess is that since most roller bearings and seals are actually made in metric sizes, this .531 equals 13.5mm, so the seals would be more readily available.  

Prop specifications,  OMC / Bombardier  #390237 propeller, (Part replaced by OMC 0778797)   8-1/2" X 9" 3 blade, (5/6/8hp models) EXCEPT the long shaft models which use a different one.    Or Michigan Wheel propeller, 1980 & newer Johnson 6 / 8hp #012032 8 1/2" X 9, 3 blade $81.99

Paint :  OMC  / Bombardier  paint, spray can,  Ivory #173744,   Johnson Platinum Gray #174069 but superseded to  #771246

 

Copyright   2011 - 2014  LeeRoy Wisner  All Rights Reserved

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Originally stated 09-20-2011, Last Updated 12-14-2014   *

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