Trim up, drifts down...

[gene8084]

I have a 1974 Mercruiser 888 Outdrive.

Need a little advice on isolating the cause of this problem.

I just completed replacement of the seawater pickup pump. I'm not sure that could have anything to do with my problem but folks always say what did you change...if you say "nothing but..." you look pretty stupid.

Since completing the pump project I find that the stern drive won't stay up after being trimmed up. rrrggg (Iwas so pleased with myself that everything worked when I put it back together)

I checked this morning, ...in about 30 minutes it drifted down approx. 10 degrees. Clearly not holding.

I don't see any leaking outside the boat. (Trim cylinders, hydralic lines, etc.) I haven't crawled back by the transom yet to look for leaks, but I'm guessing I won't find any.

We certainly wrestled a bit getting the lower unit back in place, leaning/lifting etc., but I would not have thought we could damage seals in the trim pump.

Thoughts?

 

[MercMonster]

Re: Trim up, drifts down...

I'm having a similar problem myself. It's most probably an internal trim cylinder leak. I was searching on the forum last night and found a few posts mentioning that the seals in the trim cylinder could be sticking or going bad. After looking through my Merc manual, breaking down and repairing a trim cylinder looks like even more fun than rebuilding a carb. I may just deal with it for the time being, but here's some information on some of the different parts you may need. Good luck!

 

[gene8084]

Re: Trim up, drifts down...

Just curious, how did you isolate to the trim cylinder rather than the pump itself?

Thanks for the link. Those photos are helpful for identification. I'm told I have a Model #1, but when I went to replace the sea water pump and the base didn't fit the parts warehouse said I had a Alpha 1 (at least the lower unit). I suspect my trim cylinders are Mdl #1 since the wear is similar to the upper.

 

[MercMonster]

Re: Trim up, drifts down...

Pressure testing procedures are pretty cut and dried in the OEM manual, so you'll know what is likely bad. Most alpha one parts will match up on pre-alphas. May be some exceptions that the experts, of which I'm definitely not, would know more about.

 

[wire2]

Re: Trim up, drifts down...

Can isolate cylinders by supporting outdrive in up position, undo lines and insert plugs. Remove support, wait a bit.

 

[gene8084]

Re: Trim up, drifts down...

Excellent. That's why your the Chief Petty Officer.

 

[wire2]

Re: Trim up, drifts down...

It just occurred to me, if 1 cyl is good, it will keep the outdrive up. You may need to remove 1 cyl at a time to test them individually.

 

[gene8084]

Re: Trim up, drifts down...

You read my mind. I was wondering about that. I guess I need to plug the lines also, especially if I do one trim cylinder at a time.

Any idea what size/thread the plugs are?