Prestolite trim pump...Before I disassemble, any advice?

[1lastweekend]

I have a 1981 Rinker V170 with the Mercruiser 120/2.5L motor. For the last year, the lower unit will drift down to the full down position within a few minutes of being raised. This boat has the Prestolite trim pump in it. I have checked the trim rams, lines and pump, does not appear to be any leaks and the oil level in the pump is staying full. I think it is the check valve ball/spring assy in the pump body. Luckily I have another pump assy where the motor went bad a few years ago, so I swapped it out for a used one from a local boat salvage place. I have this one on the bench now, but not fully disassembled.

I want to make sure this pump body is functioning correctly before I swap it in for the other one. Does anyone know how I should take it apart to prevent the pieces from coming out, and then not understanding how they go back together? Also how can I tell that there is leakage past the shutoff that would cause the leg to drift down? I appreciate any advice!

 

[kenny nunez]

The only way to diagnose the Prestolite hydraulic system is with the test kit that Mercruiser required dealers to have. Other than external leaks is about all you can check for. You can try replacing the block on the bottom of the pump body. If you do start to remove the pressure adjustment screws record how many turns it takes to remove each one. You can also check the rams by disconnecting the hydraulic hoses and obtaining a pair of 3/16”inverted flare fittings that are 1/8” pipe male on the other end and capping that end with a female cap. This way you can isolate each ram to see if one is leaking internally .

 

[alldodge]

Can make up your own test kit. Need a at least a 4000 psi gauge, Tee fitting and couple valves. The most costly part would be the valves

Merc stuff sells the kit for $380 where others are selling for $800 or so.

 

[1lastweekend]

Thanks for the advice! I have also seen where several places sell an Oildyne-style pump and motor that can retrofit to the models that used the Prestolite...Anyone have info on that conversion? If I have tested the trim rams and found no internal leaking, I may want to just replace the whole unit.

 

[alldodge]

Changing to Oildyne would not be an issue

 

[1lastweekend]

The only way to diagnose the Prestolite hydraulic system is with the test kit that Mercruiser required dealers to have. Other than external leaks is about all you can check for. You can try replacing the block on the bottom of the pump body. If you do start to remove the pressure adjustment screws record how many turns it takes to remove each one. You can also check the rams by disconnecting the hydraulic hoses and obtaining a pair of 3/16”inverted flare fittings that are 1/8” pipe male on the other end and capping that end with a female cap. This way you can isolate each ram to see if one is leaking internally .

Thanks for the advice, I am going to order some parts to test the trim rams for internal leaks before I go forward with the pump work...Does this look like what I need? Thanks