1978 Power Trim won't stay up!

[bgreg]

Have 1978 Bass Boat 85 hp Mercury Motor. Power trim goes up but won't stay up. Must be a o-ring problem or a valve. Does any one have a schematic of the parts for the power unit. Looked at power unit and all the hose and I assume valves are under the unit.

Thanks, Brian G

 

[Barnacle_Bill]

Re: 1978 Power Trim won't stay up!

Check your manual release valve to be sure it isn't loose. There are O rings on it that you should check too.

 

[Chris1956]

Re: 1978 Power Trim won't stay up!

Brian, Does that motor have the PTT pump and resevoir in the boat, and two trim cylinders on the motor? If so it is likely the piston seal is leaking. There is a cylinder rebuild kit available. The piston has a teflon seal, and you need a special tool like a ring compressor to reinstall the piston. The balance of the kit is orings.

The first thing to do is to isolate the trouble to one trim cylinder. To do that you will need to disconnect one cylinder at the control valve and pump up the motor on one cylinder. If it leaks down, it is bad. Repeat with the other cylinder. There is a small chance it is the control valve. In that case replacement is the only option.

 

[bgreg]

Re: 1978 Power Trim won't stay up!

Check your manual release valve to be sure it isn't loose. There are O rings on it that you should check too.

Thanks Bill,

Thought that the manual or emergancy release might be the issue. Suppose to be same unit that come with 90hp according to Richardson Annex. Faxed me a picture which can barely be read.

Was looking for a diagram so I could determine where to look. Have filler hole on top with big screw, has several smaller alan screws that are all tight. found that I got about an 8th to a quarter turn from the bottom plate bolts under the unit, may have been leaking by there, maybe not.

Brian G

Picture showed screw from bottom, just found a small regular type head screw on top, next to large filler screw, thightened and it seems to be holding better we will see in the morning.

Thanks Bill,
Brian G

 

[bgreg]

Re: 1978 Power Trim won't stay up!

Brian, Does that motor have the PTT pump and resevoir in the boat, and two trim cylinders on the motor? If so it is likely the piston seal is leaking. There is a cylinder rebuild kit available. The piston has a teflon seal, and you need a special tool like a ring compressor to reinstall the piston. The balance of the kit is orings.

The first thing to do is to isolate the trouble to one trim cylinder. To do that you will need to disconnect one cylinder at the control valve and pump up the motor on one cylinder. If it leaks down, it is bad. Repeat with the other cylinder. There is a small chance it is the control valve. In that case replacement is the only option.

Hi Chris,

Thanks for the reply.

Yes it does have the pump and motor inside the boat.

Rebuilding cylinder sounds a lot like doing the cylinder for the snow plow lift. I read a couple of threds here last night that said it may be the emergency release valve. Found what may be it and it was not real tight. Tightened it and motor stayed up a lot longer but was down in the morning. The real test is going accross the water at speed. We will see, maybe on Tuesday.

Thanks again for the advice. Would hate to get into the cylinders if I don't have to, but will if thats what it takes.

Brian G