Correct trim cylinder/ram behaviour..?

[nigel]

Hi,

I've had a leaky trim ram/cylinder so decided to give it a strip-down and re-build.. Water was getting in the fluid and one ram would drop by itself when the boat is out the water and the drive removed. Although this would take a few days.

I took both cylinders off the boat and drained the fluid out of them. The ram that I believed to be leaking would slide in and out quite easily with the fluid hose holes covered up with my fingers. No significant pressure build up either in or out.. Which I -thought- was a fault and indicative of bad seals. The ram I thought to be OK would build up air pressure against my fingers if I pushed the ram in or out... And would spring back to its original position when I released the ram.

Having swapped out all the seals plus the bearing/mechanisim/piston bit and floating piston, I expected the ram to hold air pressure and not be able to push in-or-out freely against sealed-off hose holes.. but it didn't. It behaved as before - sounding like the air is getting past the ram seal or through the bearing/kick-out mechanism.

So.. how should I expect a trim cylinder to behave when its got no fluid in? - Should it side in and out against air even with the hose holes covered up? Is, actually, the ram that builds up pressure the faulty one?

Thanks in advance for any help!!

Nigel.

 

[njmorrell]

Are these Bennett trim tabs? If so I think the rams are single acting. That is to say they have a spring in for one direction and the hydraulics only pump against the spring.

Rgds Nick.

 

[nigel]

No - I mean the drive trim rams...

 

[nigel]

These rams are driving me mad... Rebuilt and re-installed today. Without the drive on, one works fine but the port ram will not return all the way - stays about three inches out of the cylinder. Ahh... Any ideas? - Is this a seal/valve issue or air lock or maybe bad cylinder wall so one of the pistons is getting stuck?

 

[Stray Cat]

Did you drain, flush, and refill the trim/tilt pump?

If the seals are installed correctly, and the bore of the cylinder is within tolerances, if you plug the port against the direction you are trying to move the rod, air pressure will cause resistance.

You could swap the cylinders to see if the problem follows the cylinder, I suspect that it will.

One way to test your piston seals is to extend the both cylinders all the way out, remove the hose that is connected to the rod end port of the cylinder that is causing you poblems. (You may want to get have a partner for the next part) Have your helper activate the trim switch up while you watch the disconnected port for oil flow. If you have oil flowing from the disconnected port, there are issues with the piston seals. Reverse the procedure for checking the rod side of the piston seal with the cylinder retracted. Air should purge itself after 5 or 6 cycles of the cylinder at full stroke.

 

[nigel]

Thanks.

Things are getting ever-more wierd with this... I've bled all the air out the cylinders, I think, and the drive will go fully down.. Once.

Only problem is, after a couple of up-down cycles the trim won't go all the way down again. And each time I go through an up-down cycle, the amount it won't go down by gets larger - until I'm up to about three or four inches of ram sticking out.

The rams can, with a hard push, be moved - against something that compresses and then slowly returns when I let go.

If I remove the down hose, and push in/down, oil then comes -out- of that hose - which I wouldn't expect, and the ram can be pushed in. Actually, there seems to be a fair amount of pressure stored up in the down hose when I disconnect it.

Also, the trim pump often makes a kind of screeching noise when its in operation - so my current thoughts are that the pump/valves could be dying. And actually pumping air into the cylinders somehow.

Anyone know if I'm on the right track here?? - What does a dying pump/valve unit sound like?? What will it be doing if its screeching whilst pumping?

Cheers,

Nigel.