Upper Unit Drive Shaft Seal Replacement, MC-1

[Cresco750]

Gradually, I'm getting to the bottom of my MC-1's issues. The next one I need to sort out is an oil leak from the upper unit drive shaft seal. Reading through the manual it looks like there are two seals together which I would be replacing? The manual goes on to say that the entire top box has to be virtually completely disassembled in order to replace these; is this the only way or can they be changed form the bottom of the shaft?
Assuming that the whole box has been disassembled to get at the seal, I am then directed to correctly shim the bearings, check gear pre-load, etc. is this all necessary if all I will be doing s reintsling the old shims exactly as they were removed?

Is this a job for an owner to tackle, or best left o the experts?

Cheers

 

[cr2k]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

You shouldn't have to shim an existing set up. The seals are vinyl and have no metal ring to wedge in good and tight.
But yes since they are the first thing in when assembled it has to be completely dissembled.
It would be a though to use some seal/bushing adhesive on the seals to ensure they stay.

 

[dubs283]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

there are two seals in the area you refer

the lower on is installed from the bottom, outside the case - the upper is installed from the top, inside the case

yes you need to pull the drivshaft/driven gear bearing assy but do not need to re-set the preload, the shimming should be correct already, no need to change that - you only need to re-set the bearing rolling torque/preload if you take the bearing/gear assy off the shaft to replace the yoke seal

the upper dirveshaft will pull straight up and out once the driveshaft/bearing assy is out

do you have the proper OEM manual for your drive??

 

[Cresco750]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

Thanks for help, that gives me confidence to attack the job myself. I'm working with Mercruiser manuals #4 and#6, along with a Seloc manual. I find that the Mercruiser manuals are obviously written for the qualified mechanic, whereas the Seloc sometimes has plain English explanations and diagrams.

Cheers.

 

[Don S]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

whereas the Seloc sometimes has plain English explanations and diagrams.

And lots of wrong information. Be careful.

 

[Cresco750]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

And lots of wrong information. Be careful.

Yes, I have picked up on that caution on the forum before, so I just use it as a cross reference.

Just a thought; is it theoretically possible to pry out the lower seal from the outside and slip a new one in without disassembly? Would replacing the lower of the two seals likely stop an oil leak down the shaft or must they both be done?

 

[ktbarrentine]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

Check out these two recent threads on the subject of replacing the lower of the two seals.

http://forums.iboats.com/mercruiser...ha-one-bottom-housing-top-housing-588979.html

http://forums.iboats.com/mercruiser...ser-165-outdrive-gear-lube-exaust-590532.html

The lower of the two seals is not really an oil seal per se... its real function is to keep water out of (and grease in) the spline area where the vertical shaft of the lower engages with the gearing of the upper. If you have an o-ring groove on that shaft, it is highly recommended not to put an o-ring there, as it often interferes with that lower seal during reassembly and can cause problems with getting water up there (they even did away with that groove on later model Alphas). Bottom line, yes, easy to replace that seal without taking the upper apart, and even after you replace it, this seal is not subject to pressure during a pressure test (the upper seal takes care of that)...but if both seals leak, then you will see it on a pressure test (and if you pressure test the upper by itself, you will be able to see if that upper seal of the two is, in fact, leaking). Good luck.

 

[Cresco750]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

Ok, so now I'm baffled. Before I pulled the drive off there was a relatively significant oil leak; enough to fill the lower case exhaust area in front of the prop to the level of the carrier nut and then drip over onto the ground. So, I emptied the gear case and pressure tested as a unit. No pressure drop. So then I removed, split the drive and pressure tested the two halves individually. Again, no overall pressure drop, just a half PSI increase and decrease over the course of a day and night which I assume was from ambient temperature change?
There was deffinately a reasonable amount of gear oil around the shaft seal in the top housing when i split it so this is where I expected to see / hear the leak, but nothing. I tried soapy water but based on my readings there wouldn't be any pressure escaping to generate a bubble anyway.
I know that as soon as I put the drive back on the boat it will leak again, so I need to fix it. What else should I be checking?

Cheers

 

[dubs283]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

did you rotate the splined input driveshaft and shift the drive into fwd, neu, and rev while turning it??

you need to simulate the action of the drive as it is being used to properly pressure test it

 

[Cresco750]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

Yes, as best I can, and shoved a long screwdriver up not the spline and gave that a wriggle but still no drop. I don't want to just strip it apart and replace perfectly good seals, but I know there must be a leak somewhere?!

 

[Cresco750]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

So, I decided it was time to try a vacuum test of the upper box. Straight away it would not hold a vacuum, so again I applied pressure and to my relief I could hear a hissing of a bad seal. A spray of soap confirmed a bad upper shaft seal, and I also noticed that the lower seal had shifted off centre slightly, which turned out to be complete seperation of the seal rubber from its metal housing - not sure how I didn't notice this before? Now I know I need to pull it apart and replace those seals, which is good news (bad news?

Thanks everyone for all your help!

Cheers

 

[Cresco750]

Re: Upper Unit Drive Shaft Seal Replacement, MC-1

(Disregard this post of mine - I asked a silly question, to which I subsequently figured the answer out)