77 OMC Trim and Tilt Questions

[steamin53]

I need some help guys. We bought a 1977 70 hp Evinrude with Power Trim and Tilt. This is the system with the rams outside the engine bracket.

The port (trim ram I've been told) was frozen in place. The motor, pump, and starboard ram all work.

I've acquired another system and in testing on receipt I find that the motor worked, the pump extended the starboard ram but not the port side. In a third sequential cycling of the sytem at the end of the starbord ram's travel the port side ram extended about 4 inches then it stopped. Reverse the system and the starboard ram retracted but the port ram does not and it feels like it is solidly locked where it is.

I've been told that the port ram has no hydraulic pressure to it at all which seems to be impossibly or unlikely at best since it has a hydraulic line to the bottom of it. I conclude that since the starboard ram has hydraulic lines to the top and the bottom it has hydraulic power both to extend and to retract and that perhaps the port side only has power to extend.

Either way, I'm concerned now since the port ram won't retract no matter how hard I push on it with my hand.

Anyone able to advise me on this?

I SHOULD ADD THAT THE SYSTEM IS NOT MOUNTED ON THE ENGINE FOR THESE TESTS. I wonder if the port ram requires power from the starboard ram in the retract mode to go down?

Steve

 

[RRitt]

Re: 77 OMC Trim and Tilt Questions

the port ram may be built to only hold pressure during trim. Above four inches it might and move freely but below four inches only move if the pump is running. one of the rams (is it port? or is it starboard?) is trim and the other is both trim/tilt.

 

[steamin53]

Re: 77 OMC Trim and Tilt Questions

I'm not clear on your meaning but at present it will not move to extend or retract.

 

[RRitt]

Re: 77 OMC Trim and Tilt Questions

imagine a cylinder with 1" bore for four inches and 1-1/16" bore the rest of the way up. It would lift great for the first four inches but if you go any higher then it just flops about. As far as trying to manually shove the thing back down it would be pretty easy until you hit four inches. Below that it would be rock solid unless the hydraulic pump was running.

 

[steamin53]

Re: 77 OMC Trim and Tilt Questions

RRitt are you trying to say that I must have the pump running in the retract mode to be able to push the port ram down? That does make some sense as it only appears to have hydraulic pressure applied to the extend mode since there is a line only to the bottom of the ram.

I haven't tried that... yet!

I've run the starboard ram down all the way under power (noting that the port ram does not go down with it) then tried to push the port ram down without the pump running.

 

[ezeke]

Re: 77 OMC Trim and Tilt Questions

Maybe the diagrams will help the discussion.

The trim function works during approximately 15 degrees of travel and can offset the force of the engine when underway. After that, only the tilt ram is in play and can move the motor only at low RPM or with the engine off.

The third thumbnail highlights the section of the factory service manual which explains it better.

 

[steamin53]

Re: 77 OMC Trim and Tilt Questions

Thanks Ezeke, excellent information! I can't tell you how many posts I've seen on the net looking for that exact diagram set.

Given that I'm testing this sytem dismounted from the engine, should I be able to retract the trim ram or does it have to be coupled to the hydraulic power of the tilt ram in the retract or "down" mode via their mounting on the engine?

Also, do you have any clue as to why I initially had to cycle the tilt ram to fully extended position and back to fully retracted three times before the tilt ram moved and then only at the end range (full extended) position of the tilt ram?

Steve

 

[ezeke]

Re: 77 OMC Trim and Tilt Questions

The port trim ram is going to give the extra force needed when in the trim range to push the motor away from the stern. Coming in it just follows.

Any delay initially is probably from air in the system. Cycling the closed system up and down will usually clear the air if you keep adding fluid.

RRitt is an expert in these hydraulic systems, so he will have a better answer regarding a closed cylinder like that.

 

[RRitt]

Re: 77 OMC Trim and Tilt Questions

Thanks Ezeke, excellent information! I can't tell you how many posts I've seen on the net looking for that exact diagram set.

Given that I'm testing this sytem dismounted from the engine, should I be able to retract the trim ram or does it have to be coupled to the hydraulic power of the tilt ram in the retract or "down" mode via their mounting on the engine?

Also, do you have any clue as to why I initially had to cycle the tilt ram to fully extended position and back to fully retracted three times before the tilt ram moved and then only at the end range (full extended) position of the tilt ram?

Steve

you are going to have to let the fluid out for it to lower those last four inches. The easiest way is to run the pump so that the check valves are open. You could also just unplug the tube and let it squirt into a bucket.

 

[perculator]

Re: 77 OMC Trim and Tilt Questions

you are going to have to let the fluid out for it to lower those last four inches. The easiest way is to run the pump so that the check valves are open. You could also just unplug the tube and let it squirt into a bucket.

i'm working on installing mine also. my trouble is that the port piston is physically bottomed out in this picture. the starboard cylinder has full range of motion while the port only moves about 3-4" from this bottomed out position.
am i missing something here with regard to how this operates? just looking it doesn't appear that the port piston will allow the motor to go full down.
here's a couple of pictures as it sits now.

 

[ezeke]

Re: 77 OMC Trim and Tilt Questions

When you have them connected they will work as they should.. You should probably run the starboard ram up so that they are more even, then move the motor to make connecting easier.

 

[nathanhooper]

Re: 77 OMC Trim and Tilt Questions

I am working with percky boy, helping him with his equipment on the boat. I do not mean to discount the very knowledgeable advice given, but in the physical sense this just does not seem to work.

When the port side (trim) cylinder is bottomed out, physically at the bottom of cylinder, verified with the hose disconnected and looking through the tapped hole, you can see the bottom of the piston. When it is in that position it will not allow the motor to go any farther down than what you see in the picture. Well, a little, but the picture shows it bottomed out and how far up the ram still sticks out.

If it is physically attached to the motor, and to the transom via the bracket, then how is it going to allow full range of motion when there is no where for the piston to travel too?

Again, maybe if someone has a video of how it works on a boat then it may make me feel as though I am crazy. But as it stand, not trying to argue with anyone, it just does not make much sense in the physical workings. Please advise.

 

[nathanhooper]

Re: 77 OMC Trim and Tilt Questions

Well, after some evaluation, we just figured out that the trim ram "rides" inside of cylinder in a separate housing. It must be frozen in there because it will not allow it to reach the bottom of that housing. We were under the impression that it was one complete piece inside the cylinder, when in reality it is two separate pieces.

Sometimes it just helps to talk things through. Thanks for the help, could not have figured it out without the diagrams.

 

[perculator]

Re: 77 OMC Trim and Tilt Questions

ezeke....how do you remove the ram from the housing?

 

[RRitt]

Re: 77 OMC Trim and Tilt Questions

It goes up and down and its just the telescoping part thats stuck? if you hook it up and lower it like Ezeke says then the tilt ram might be strong enough to pull it down. That's over 800Lbs of downward pull.

 

[perculator]

Re: 77 OMC Trim and Tilt Questions

we'll take it back apart and see if there's anything we can do. in the end we may have to just hook it up and see.

 

[RRitt]

Re: 77 OMC Trim and Tilt Questions

Taking it apart is going to put you in a situation of needing new parts no matter what. You can't reliably re-use seals, gaskets, or orings. Your stuff looks in very good shape. Very, very good. It might have just been sitting for long time and needs to have surface rust broken free. IMO, you should do like ezeke says.

 

[nathanhooper]

Re: 77 OMC Trim and Tilt Questions

I have had it under about 1000-1500 psi from a press and it didnt budge. I think that whether we like it or not it is going to have to come apart. Once the assembly is removed from the cylinder housing, how do you take the rod out of the sleeve it rides in?

 

[RRitt]

Re: 77 OMC Trim and Tilt Questions

I have had it under about 1000-1500 psi from a press and it didnt budge. I think that whether we like it or not it is going to have to come apart. Once the assembly is removed from the cylinder housing, how do you take the rod out of the sleeve it rides in?

with as little damage as possible. If you need anything other than the bearing it may end up costing $200 (or more) in parts. How much is the trim worth to you? You know that it will tilt just fine without that thing.

 

[perculator]

Re: 77 OMC Trim and Tilt Questions

so if i didn't have the port (trim) cylinder then it would just limit my ability to trim while underway?