boat hoist uneven lift

[timmer4654]

I bought a used Hewitt 4100 hydraulic cantilever lift that will not raise my boat evenly. The boat starts off level and then gets tilted to one side (rather dramatically) and then levels out as it reaches its highest point. A picture is attached but the video (link attached) better illustrates the problem.

The two cylinders have been rebuilt and are not leaking and do not float from any given position. The cylinders are in simple parallel with no flow control between them. The connections to the carriage are not binding or out of round. The tilt occurs both when raising and when lowering the boat (the video illustrates this well).

Anyone have experience with hydraulic cantilever lifts?

 

[GA_Boater]

Welcome aboard.

Have you tried bleeding?

This probably falls in the "jerky" category;

 

[timmer4654]

Thank you I had already seen that video (and all the other Hewitt videos) and, you are correct that it is more specific to jerkiness on the way down - it has nothing to do with raising the boat unfortunately.

 

[GA_Boater]

Have you tried the steps in the video? It says raised and lowered.

I never said anything about being jerky going down?

 

[timmer4654]

Yes - I have adjusted the valve that is shown in the video and raised and lowered the unit many times over the past few weeks. It has rested in the up position and it has rested in the down position - with load and without load. Sorry, didn't mean to misrepresent your comments.

 

[Horigan]

Given that the cylinders are powered from a single source, that would point to either more friction on one side or the mechanism geometry isn't the same on both sides (one side slightly bent?). Since the same side is lower going up and down that would exclude friction. I would inspect for any damage on the mechanism members or links. Seems acceptable now. I would monitor it to see if it gets worse with time (something bending more).

 

[JimS123]

Right off the bat you can see that the bunks are not properly adjusted. As the video showed it going up I could just imagine the boat tipping over.

 

[timmer4654]

The bunks sit on pins that allow them to pivot on their own to adjust to the bottom of the boat, which actually has been a source of frustration to me because they often flop over. How do you mean that the "bunks are not properly adjusted"?

 

[JimS123]

The bunks sit on pins that allow them to pivot on their own to adjust to the bottom of the boat, which actually has been a source of frustration to me because they often flop over. How do you mean that the "bunks are not properly adjusted"?

They are too close together. If they flop when you don't want them to, tighten the bolts slightly.

 

[timmer4654]

I have the same concern about the bunks being too close together - however, the distance between the bunks is not adjustable. I'm not sure if you can see the image in manual I attached but the bunks are connected by a sort H-shaped frame that is solid and, by design, does not allow them to be separated further.

 

[JimS123]

Never saw one like that without some sort of adjustment. Maybe you should contact the manufacturer and ask them what to do to fix your problem.

 

[dingbat]

Quite surprised they don’t have some sort of port or flow controls in the system to compensate for unbalanced load conditions.

Does it go up evenly without the boat?

I would try restricting the return controls (fix jerky action) to see how it reacts. If that doesn’t work, run each cylinder separately with a pressure gauge in the pressure side. Pressure should be the same on both lines.

If not, disconnect the cylinders from the lift to see if cylinders travel at the same speed. It’s possible that something is caught in the port restricting flow until the pressure builds enough to past the restriction

 

[timmer4654]

Good suggestions, all! Thanks.
JimS123 - I have contacted the manufacturer and their local reps who not particularly helpful other than telling me to buy new cylinders (at over $800 each) and new lines.
Dingbat - Without load the lift raises somewhat uneven but nothing like when loaded. Unfortunately, there is no valve in the system to isolate individual cylinders.
And I thought about the possibility of a restriction somewhere but with such high pressure and since the problem occurs with pressure in either direction (raising and lowering), it seemed to me to be unlikely at first - but I guess I have to persue that now.

I think the next step is to have it pulled out of the water again and try swapping the hoses between the cylinders to see if the problem follows the hoses. Then swap cylinders to see if the problem follows a cylinder. But I can't test it under load out of the water very easily.