1977 Mercury 1150: Trim Cylinder Leaking at Piston Rod/Retaining Cap

[kck8385]

My 1977 Mercury 1150 trim cylinder is leaking out of the piston rod at the retaining cap. My trim has the 3/4" piston rods. I know this is probably just the 3/4" o-ring in the cap.
Should I just find an o-ring locally to replace the one that leaking or buy the Mercury kit and replace them all? The Mercury kit is #64507A1 for the entire cylinder.

The o-ring locally would probably be a dollar or two. The kit from Mercury is probably $45 per cylinder.

Thanks,
Kevin

 

[Chris1956]

if the trim is holding up pressure, and not leaking anywhere else, I would replace the cap oring only. You need a special tool to install the piston and it's teflon seal into the PTT cylinder, so you do not want to pull it out of the cylinder,. The PTT cylinder is steel and is inside the trim cylinder housing.

So, remove the ptt cylinder from it's mounts. Fact the trim rod up. Use a spanner to open the cylinder cap. Pull out the trim rod, making sure the cylinder comes out as well, and the piston stays installed in the cylinder.

Unbolt the piston from the trim rod, leaving it in the cylinder. Pull the trim rod out of the cap. Replace the oring. inspect the trim rod for burrs. Smooth with 400/600/1000 grit sandpaper if needed. Oil and reinstall.

 

[kck8385]

Chris,

Thank you for the information. You have helped me a lot over the past few years with this motor. My Mercury service manual and parts manual show a different cross section diameter for the o-ring. Service manual says it is 3/32. Parts manual says 1/8. Does it actually matter which I get. Also is any o-ring material better or worse than another?

Thanks,
Kevin

 

[Chris1956]

I really do not know the different kinds of Oring materials. I would guess that Nitrile is better.

I would recommend you look up how Orings are measured (usually in three directions), and match the OEM specs as close as possible. Most important is that there are no burrs on the trim rod, as that will tear any oring.

 

[kck8385]

Chris,

Thanks for the response.