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1968 Mercruiser 120 oil leak @ upper shift shaft

Fisch

Fisch

New member
I recently did a water pump repair on my Mercruiser 120 (pre-Alpha, MC-1) and had it out Tuesday ... everything is/was seemingly wonderful ... that is, until I noticed a small circle of oil in the driveway.

Further detective work revealed that this oil is coming from the upper portion of the shift shaft in the bell housing (I believe) ... and it very small ... a very minimal drip.

Fearing that some sort of seal had been compromised, I drained the oil today to look for signs of water and ... NONE.

Question being, is this a big deal? Sometimes normal on an old unit? Should oil even be in this part of the drive? If not, possible places it could be coming from? How labor intensive is a repair, if that's necessary?
 
Well ... upon further review, I presume that the exhaust bellow is bad, after running her on muffs this afternoon and seeing a slow water drip near the front most part of the bellow (near the transom).

I also saw a slow water drip from the same spot that the above mentioned gear lube came from. Now, while it would seem logical to see water there if the exhaust were traveling through this area, oil would not. Is it likely a seal is blown if oil is somehow in here? What seal is most likely?
 
shifter.jpg


bellow.jpg
 
So #20 would allow gear lube into the exhaust passageway if it were blown?

It appeared to stop after a day or two (only lost a couple drops a day) ... so then I trimmed the unit down, and later that day saw a small amount of oil leaked from a water drain on the side just below the water inlets.

Curious, to be sure ... and as stated above, I am FAR from knowledgeable on these.

Another thought I had was that after looking at schematics, I see that the upper shift shaft has a bushing on the bottom (which seems unimportant with regard to seal) but it also has a bushing at the top which seems like it might be relied on to act as a seal as well. No?

Thanks again for any input ... I'm lost and trying to avoid shopping her ... but definately want to know what direction to head in when investigating.
 
Ah ... I see ... never had the whole drive off before, so was not at all familiar with the 'guts' and what things looked like.

Your screen name suggests you're a marine mechanic ... on a scale of 1-10, where do you rate the difficulty on this? Is this seal pressed in, or can it be changed with basic tools? (if of course, it proves bad) ...

Thanks!
 
First problem

1968 = 42 years old...................I am not suggesting there is anything wrong with old boats but from your last post you are not very knowelgable of boats? correct?

WHy would you purchase such an old boat?

There is NO WAY you are NOT going to have a ton of problems if for no other reason other than bieng 42 years old................

If you have limited or no knowledge of boat mechanics you may want to find a local person who does.

Trying to get answers here from people 100's to 1000's of miles away may be difficult especially if you hvae limited or no knowledge of boats and especially outdrives.......

Just my opinion ................

Got to ask, Why a 42 yeear old boat? The oldest boat I would even consider would be mid '80's. There was some major improvements from the '60's to the 80's and stayed fairly consistant thru the '90's
 
Well ... I've owned the rig for close to 10 years ... don't log a ton of hours per season ... maybe 25 or 30, mainly fishing ... not pulling tubes around or anything ... the boat was had for 2000 bucks with a rebuilt 1987 120 (prev. owner cracked the block on the original, which I discovered and talked him into the new engine as a purchase condition) ...

A local mechanic installed this engine (he was the rebuilder too), and at the time everything was cherry outdrive wise.

Now, I'm not 100% novice. I know about basic maintenance and have owned outboards prior to this boat. I've simply never dove into things that are seemingly more major, and having never done so I'm simply trying to evaluate what I may or may not be getting into before determining if I will attack it myself or seek professional help.

Having read quite a bit at this point, I'm seeing that Mercruiser has special tools for quite a few things on these (did they teach this to Mr. Goodwrench too?) ...

Final thought on the old boat thing is that when I look at my 1954 Johnson kicker motor that runs like a raped ape and look at my Dad's 1988 Force that may be the biggest Marine turd ever passed, I'm a firm believer that the days of real quality are historic.

Of course seeking input is the primary reason for discussion forums, is it not? I'm sure if I looked hard enough I could turn up somebody who has done this type of thing in my list of acquaintances but there's a certain satisfaction to be had when you do a job, any job yourself.
 
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Ditto!

Well then first thing you must do is drain the oil from the outdrive. Secure a pressure checking device, ( a hand pump with a guage installed between the pump and the outdrive and pump it up to 15 psi).

Of course you must reinstall one of the plugs either drain or vent (top or bottom) when doing the pressure check.

It should hold for at least 2 minutes with no change.

By doing this this will expose any leaks. You should be able to hear the air leaking out. If the bad seal is inside the two halfs then it may be necessary to split the two halfs to find/hear where it is comming from.


If no leak down on guage then NO problems.

If you are getting water in the gear oil and the pressure check does not show a leak then you need to pull a vacuum on the drive. at least 4-6 hg to see if there is a seal leaking in but not out.

here is a link to what I have and use.....

http://www.stevensinstrument.com/gearcase.htm

of course you can make your own with some simple components. I needed proffessional grade......
 
I agree with your statements with this issue he has.

Also he has owned this for 10 years and never removed the drive from the boat. this should be done every year to insure the unit is greased and inspected for leaks/failure issues.

having a shop manual and tools to repair is needed..then alot of knowledgeable maintenance actions to keep this old unit running.
 
Oil in the bellows can only come from the carrier seal.To leak from the shift shaft means it`s getting past the rubbder ring seal and into the shift cable area. To remove the drive shift into full fwd, remove the rams, 6 nuts and it SHOULD pull sytraight back and off.If it dosent, suspect water intrusion and shaft stuck to gimbal bearing . The "Difficulty Scale" depends on what you find inside.
 
Maintenance like U-joint greasing, etc. was only learned earlier this year when talking with a co-worker who has some limited knowledge, being an owner himself. I could kick my own *** for not learning a bit more about these when I initially bought it, and hope I've done no damage in the meanwhile.

Anyhoo ... back to the problem at hand ...

I've started tearing back into things before reading the last couple of replies from you fellas ...

I tore off the lower unit yesterday hoping only to get a look at the where the oil was seen coming from, and to determine how it got there.

Here's my first look:

wateroil.jpg



Now, as described earlier ... after last running it on muffs, I naturally had water slowly dripping from here first, for a short while after shut down, followed by oil. This was with the unit trimmed up so naturally, some water would pool here in this position and any oil would float to the top of it, coming after the water COULD drain, drained to this point.

After a day, I trimmed down and the balance of the water and a tiny bit of oil drained ...

My logic at this point, and correct me if it isn't sound is that this oil can't be truly coming down the shift shaft necessarily (from the rubber seal bt doctur described) because if it were, it would continue to leak here and pool up in the water pump area (exhaust passageways) ... or so I think.

Further examination however did reveal this:

seal.jpg


seal2.jpg


So if I'm looking at the schematics correctly, this seal retains oil in the upper gear housing and being blown could perhaps allow oil into the exhaust area via the drive shaft, and possibly only when the unit is running, under pressure, and not allow water back upward, thus explaining the lack of water in the oil. Even sitting idle, my logic tells me that this seal is above the water line (or damn near), so other than incidental splash from the exhaust area it would not see sustained water exposure to allow water to eventually penetrate and pollute the oil.

This is my logic anyway, and correct me please if it's not sound. The old girl also has an o-ring on the drive shaft near the top that was torn (even though it was replaced when the water pump work was done) ... and the seal appeared good at the time of the water pump work ... although it was obviously not ... perhaps damaged from heat during the water pump failure?

So that's where I'm at ... still haven't pulled the entire unit ... just the lower, based on time constraints yesterday afternoon.

I can't discern if the seal is #29 or #30 on the drawing that bt doctur provided in the link above, but I suspect replacing both is obviously prudent.

Does the entire upper unit have to be torn down to access this seal, and is this seal pressed in?

Thanks again for all of the correspondence guys, I'm learning a good deal here as I go along.
 
the shift rod area in the lower portion of the lower unit should have a drain hole so that when out of the water this area will drain out. I have found with this not draining this seal / shaft gets damaged ..make sure the shaft is smooth .try to clear out the drain hole in the casting.

the seal only is pressed in or you can get this already pressed in with a new seal fixture.
 
j cat said:
the shift rod area in the lower portion of the lower unit should have a drain hole so that when out of the water this area will drain out. I have found with this not draining this seal / shaft gets damaged ..make sure the shaft is smooth .try to clear out the drain hole in the casting.

the seal only is pressed in or you can get this already pressed in with a new seal fixture.
Click to expand...

The drain you refer to is the tiny hole just above the drain plug, I presume? All other drains seem good, but I've never seen anything come from this hole.
 
The seal pictured is #29 and just seals the water where the driveshaft enters the lower gear #25. #30 is the main oil seal and the requires somes dis-assembly to install. #29 can be just pressed in from the bottom.The oil leak you have is from the upper unit carrier seal #20. Pull the upper unit and you will find oil in the bellows, trust me.Failure to check may just cost you a new upper unit from lack of oil. like this guy.
44593f1f.jpg
 
Not to repeat myself but I will repeat myself........

you can NOT diagnose a seal leak by looking for it!!

You must pressure check the lower and upper either when together or apart but they/it must be pressure checked.

Like BD said the seal in your hands just keeps the splined area of the vertical drive shaft from water intrusion and does not seal oil from leaking. There also is most likely a oring or two lost in there as well as they tend to peel off the shaft when the lower unit is removed.
 
Start with a new water pump kit including base and gaskets and O-rings. It's long over due anyway. You can buy a kit that has everything you need from this site. Make sure what comes out of your old pump kit goes back in the same order for the new pump kit. Clean everything really well. Then put the drive back together and pressure test it. I can't tell from here but I would say your water pump housing is leaking as well as the tiny O-ring that's next to it. That's your water and your oil mix. Make sure to use some sort of sealant on that little o-ring but don't block off the passage. And make sure the mating surfaces are clean and free of grit and paint where that o-ring seals.
 
"paint where that o-ring seals".

this is what I had to deal with several years ago. need aluminum primer for aluminum metal . I used zinc chromate then painted with mercrusier black. still looking good.. also any drive metal unpainted needs this done.
 
Thanks again for all input, guys. Haven't had the opportunity to get back at it yet (with work), but am taking all advice at this point and hoping to get to it soon ... talked to a buddy about a tool he has we might be able to pressure test with ... trying to avoid dropping 100 bucks that could just as easily be spent on shop labor before it's all said and done ... haha ... although if I must, I will of course ...
 
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