1985 50hp Mariner hydraulic pump leaking

I recently inherited a 1985 50hp Mariner on a 16ft Princecraft, and when I bought it, the hydraulic pump was seized and not working. I managed to find a functional one from a 79 mercruiser, same pump, so I know all is well there. However, I went to hook it up, swapped out the valve control from the 2 hose mercuiser to my 4 hose mariner, pressured up the system and the motor went up great, but when coming down, the pump started leaking from the bottom of manifold plate that goes between the valve body and valve control. I have taken the unit apart, cleaned all the seals, the plate, ensured all the screws were tightened properly, went through everything and all seems to be in working order. It does not leak when going up, just when going down.

When I examined the manifold plate, there were 4 holes on it, one that is relatively large, followed by two that are smaller and same size, and lastly, one that is the size of a pin-hole. I currently have it installed so that the pin hole aligns with the two holes that have an oblong/oval shape. Is this correct? could this be a source of my problem?

HELP! I'm rebuilding this boat and this system is holding me up... or if worse comes to worse, is there a way to change out the hydraulics for a gas assist lift.

Re: 1985 50hp Mariner hydraulic pump leaking

I did that today, but then it started leaking before I even turned it on. The only difference this time was that I had put oil on the manifold plate in addition to the new rings. Should the plate have been dry? What are the possibilities of the plate being warped?

Re: 1985 50hp Mariner hydraulic pump leaking

OK, so I took apart the valve body, the manifold plate, and the control valve assembly, cleaned everything off again, and then reassembled it - making sure to tighten the nuts evenly all around. Filled up the reservoir, and then trimmed the motor back up. The motor went up without a hesitation and no leaks. As soon as I pressed down, oil was pouring out of the right hand side of the valve body when looking at it from back (bracket side). I stopped trimming down and the leaking stopped. So it only seems to be leaking when it is being trimmed down.
Thoughts?

Re: 1985 50hp Mariner hydraulic pump leaking

To be honest I'm not entirely sure where I would even look for those balls that would have been used - I don't see any, just hex screws all around. I've added 3 pictures to give you an idea of what i'm looking at.


This picture just illustrates where the leak seems to be coming from - between the bolt holes, a bit closer to the right side.

This picture i took from the left side of the pump looking down as the motor was being trimmed

This picture is taken from the back, looking straight down towards the assembly.


I'm running out of ideas... would it make a difference if I swapped the VB from the original pump with the one that on my replacement?? Seeing as how I've already swapped the manifold and CBA

Re: 1985 50hp Mariner hydraulic pump leaking

Yes they are lined up as the manifold has screws to help secure it in place.
The reverse lock, I know has been left disengaged for the past 10 years at least to allow the motor to be used as a manual lift. How would one unstick that valve?

Re: 1985 50hp Mariner hydraulic pump leaking

Is there a way to test it? Cause I've had it closed and open and when the lock is engaged, the motor doesn't go down, and when it's open it will freely move... Hmmm

Re: 1985 50hp Mariner hydraulic pump leaking

Oy! I have a hunch I'll be S.O.L.... Now to figure out if I can do a manual assist/lock system.
Side question, given that I have the control valve assembly for a 79 mercruser, would it be possible to convert the 4 port system to a 2 port system through use of y-adapters??

Re: 1985 50hp Mariner hydraulic pump leaking

What would you do if you were me? Would you scrap the pump and figure out a system of manual tilt etc?? If so, how would you rig it up