1978 mercury 800 hydraulic issues.

[Jake222]

My hydraulic motor pump is out on my project boat. Tested the motor directly. No motor turny. Have to get a new motor / pump. It’s a 4 hose system. Not sure if these pumps I’m finding online are 4 hose. I believe it is a pre alpha 1978 mercury 800 80 hp. 2 separate cylinders for trimming. Any recommendations. The part number listed on the device is 105921. I also have some pictures. Thank you!

 

[racerone]

Your location ?

 

[Chris1956]

If you are looking on fleabay or similar, you will want to look for an outboard PTT pump/reservoir. They were used on a lot of Mercs (inline 4/6 models) from the early 70's until the early 80's.

There used to be an aftermarket replacement motor/upper reservoir available from ARCO (if memory serves). Not sure if they are available, however, if you find one, make sure the motor armature on the old and new motor are the same length, so they drive the pump.

Have you taken it to an automotive starter/generator shop? They might be able to rebuild it,

Actually, do they still exist and rebuild starters and gens?

 

[racerone]

It looks like there is a lot of work to be done on the boat before you need that pump.-----Quite likely it was submerged at one tme judging by the rotten lumber in the hull structure.------I would take the cover off the motor.----Rusted upper bushing on the armature.-------Might be stuck brushes or dirty contacts on a thermal overload device if equipped with that.

 

[Jake222]

Ill try that before ordering. Yes the boat needs a new floor along with stringers and everything else. it was sitting outside for close to 8 years, I am located in texas near austin. bought it because it was very cheap and the starter turns the cyclinders and the compression is good.

 

[Jake222]

I ripped out the floor and will be installing a new one soon with marine ply and glass and new stringers.I was able to find some motors that look similar but I dont know if the housing is the same size. I found a couple of the same ones on ebay that Im looking into.

 

[merc850]

My pump died a few years ago and it was from worn brushes, I bought the whole end cap from my Mercury dealer and fixed it. Here's what it looks like inside

 

[Jake222]

I have isolated the problem and concluded I will be replacing this part.

 

[Jake222]

Is there any way I can confirm that my cylinders are holding pressure. They are squirting our stuff but I’m not sure I can confirm pressure.

 

[merc850]

Where is the stuff coming from the rams or the hoses? Bad seals in the rams will cause leakage. The only way I know to check the system is to replace the pump and pressurize it.
When you have the system set up I'll post the bleeding procedure.

 

[Jake222]

Awesome. Thanks! I’ll post in this thread.

 

[Jake222]

Ordered a hole new motor pump assembly that came with the same cylinders. Really surprised I found it. But the guy says it works. At most I’ll need new hoses if they are leaking but when I took the hoses off I could feel pressure with my fingers so that’s something.

 

[Chris1956]

Jake, the weakness of the cylinders was their tendency for the threads where the hydraulic hoses connect to strip. Be really careful not to cross-thread or overtighten the hose connections.

 

[merc850]

This could be the wiring diagram for your new pump

 

[Jake222]

Will do. Thanks for the tips.

 

[Jake222]

Got everything figured out and fixed . Some work for big dreams.