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89 120hp lower unit seals

J

john_day

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I've just noticed oil leaking out of my lower unit around the prop shaft and assume a seal or oring has failed. Funny that this has just happened. I didnt have any leaking while the boat was in the water last year or any leakage until recently.

Is replacing the seal, etc. something I should attempt or is it best to send to a mechanic. I do have the factory service manual and somewhat mechanical, but in reading the manual the process does seem to be involved. I would also hate to miss what caused the leak in the first place.

Am I over thinking this?

John
 
Over thinking? Possibly.........

Are you sure it's leaking at the propshaft, that is... have you taken the propeller off and pinpointed the leakage area?

If indeed the propshaft seal, that would be somewhat unusual as there are two (2) seals there... one facing in, the other facing out. One keeps the gearlube in, the other keeps the water out.

Usually the leakage is due to a failed large O Ring at the other end of the carrier assembly.

In either case, you can remove the carrier assembly with a large slide hammer incorporating a steel rod that has a hook on the business end of it... or purchase the special tool mentioned in the manual.

If indeed the leakage is the propshaft seals, you could also use a thin blade screwdrive between the seals and the propshaft to pry them out BUT that is a rather touchy procedure unless you're very mechanically inclined.

Now... usually what one encounters (unless the prop is removed) is that the unburnt gas/oil mixture has drained down thru the long carbon/soot coated exhaust housing and that very black mixture is dripping out, running down the lower unit skeg (normal). Lets hope you're one of the lucky ones. (Compare what's leaking with what's in the lower unit).
 
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Joe, thanks for getting back to me so fast.

I have taken the prop off and the oil is definitely from the lower unit, not the exhaust. I said seals but was just assuming that would be the problem.

I see a large o ring between the housing and two retaining rings. Is it a good idea to replace the seals at the same time, or just the o ring. Replacing the o ring looks pretty straight forward. The manual gives directions for a complete tear down and I wasn't sure where to stop.

Should the thrust bushing behind the prop just slide off or does it take the slide hammer to remove it. Mine is on the prop shaft tightly.

John
 
The first step is to drain the oil and pressure test the gearcase.----That is how you determine leaks in lower units.
 
john_day said:
I have taken the prop off and the oil is definitely from the lower unit, not the exhaust. I said seals but was just assuming that would be the problem.

I see a large o ring between the housing and two retaining rings. Is it a good idea to replace the seals at the same time, or just the o ring. Replacing the o ring looks pretty straight forward. The manual gives directions for a complete tear down and I wasn't sure where to stop.

Should the thrust bushing behind the prop just slide off or does it take the slide hammer to remove it. Mine is on the prop shaft tightly. John
Click to expand...

John... I assume that you are saying that the large O Ring is definitely the item that is leaking.

Just remove the carrier assembly and stop at that point. DO NOT remove those two snap rings or the reverse gear thrust washer/bearing.

Even though the seals aren't leaking, since the carrier assembly is off, you could replace them if there's any doubt in your mind that they might be failing. However, if you don't need to replace them now but may need to a few years down the road... Hey, you'll have the knowledge and the tools to do it so it shouldn't be a big problem.

The prop thrust washer should slide right off... somebody didn't grease the shaft? Tap it a few times, it should practially fall off.

I strongly suggest using the replacement for the OMC Adhesive is now Bombardier 3M Product #847 on that large O Ring. There are some who use just grease, other may use Gasket Sealer which is available at any automotive parts store... a matter of opinion. My choice is due to not ever having to do the same job twice.

While cleaning the inner surfaces, throw a good size rag in first to protect the gears etc from dirt.
 
Joe, I'm fairly confident it is the o ring leaking now. I'm going to replace the seals while the assembly is out, no reason not to.

Thanks for the advice on the adhesive and thrust washer, your help is greatly appreciated.
 
You would use soapy water and if wee bubbles show up then there you have found a leak.--------No bubbles = no troubles.
 
Should you have a problem with building the tester..... a standard compressor can be used in a pinch as follows:

(Checking Gearcase For Leaks)
(J.Reeves)


Remove the large slotted drain/fill screw from the bottom of the gearcase and also the identical looking screw that will be located up near the cavitation plate in order to drain the gearlube.


After all of the lubricant has drained, install one of the slotted screws, whichever your preference might be.


Apply 7 to 12 pounds of air pressure to the open screw hole. Use a piece of rubber fuel line or something to create a tight air hose fit if you do not have a proper fitting.


If a leak exists, that pressure should allow you to locate the leak by sound and/or sight.
 
My 1998 200 lower unit has a puddle under it and it smells like gear oil, I'm just trying to isolate the problem to seals or O-rings...
 
nicknack2 said:
My 1998 200 lower unit has a puddle under it and it smells like gear oil, I'm just trying to isolate the problem to seals or O-rings...
Click to expand...

nicknack... Best to start your own topic post. Go back to the previous page and click on "Post New Thread" near the top left of the page. Also.... see my reply #10 above.
 
Joe, just wanted to say thanks for the help. The bearing carrier came out without any difficulty. I cleaned everything real good, replaced the o-ring, anode and both seals and reassembled. Much easier than I thought it would be.

Racerone, did a pressure test with neighbors compressor and it did well. Thanks for your suggestion.

John
 
john_day said:
The bearing carrier came out without any difficulty. I cleaned everything real good, replaced the o-ring, anode and both seals and reassembled. Much easier than I thought it would be. John
Click to expand...

We knew you could do it.... saved yourself a bunch of bucks! :)
 
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