Vibbbbbbbration!

I've got an elderly Universal 25 diesel on my 1981 E36-RH. When I run the engine at various speeds in neutral it feels as smooth as a barber shaved face or the often praised baby's bottom, but when I put it into gear that's a much rougher story. In gear I can run the boat only up to a certain RPM and then the heavy vibration starts. If I reduce engine speed to a certain point the vibration stops and the whole thing runs smoothly pushing the boat forward at about 4 to 4.5 knots on the knot meter. It always vibrated at the higher speeds but these days it seems worse. I can still rev the engine and get the boat to move at about 6 knots top speed, but my kidneys are not able to deal with the prolonged motoring any more. I'm not sure what the problem is? If the folding prop is out of balance would it not vibrate at all speeds? Something is out of balance... Suggestions please! HELP!

Steve Schwartz

alignment, cutless

You might want to try checking the engine alignment by unbolting at the coupler (mark the mating of the coupler halves first for re-attachment) and doing the procedure with a feeler guage in thousandth's. You'll probably find a more detailed procedure in this forum or in Nigel Calder's boat maintenance book. I think it's only supposed to be out at most one thousandth all the way around.

Another suspect from the wear aspect is the cutless bearing. Though mine otherwise felt tight, when I replaced it I found that it had become hyperbolic with only a smaller area in the middle of the 4 inch length in healthy contact. I don't know what the tolerance is but it isn't supposed to move much laterally. Again, a search in this forum or Calder may address that.

One time I even had a propellor become a little loose because of the wrong installation nuts and technique.

This spring I replaced the cutless bearing and installed a flexible coupling at the same time and the resonant vibrations disappeared along with a lot of noise.

Beyond that you might try one of those mouthguards that the boxers and football players use

Niel's suggestions are right on, but before you start taking things apart at this time of the year I'd also look to see what is growing on your prop and shaft. I had at least a 1/2 inch of various forms of life on mine. You may have something growing on one of the prop blades which would cause the vibrations.

Other possibilities... broken motor mount (sometimes very hard to spot when at rest unless you can lever up the engine and see the broken bolt) or even a broken strut. The later would maybe explain why it gets a lot worse in unison with the rise in revs.


Loren

And to add to Loren, my first thought is motor mount, and it may not even be visibly broken. Look for collapsed/squished rubber in the bushings. I've attached a picture of a fairly typical mount on a Yanmar. If you have a similar type mount, there should be reasonable clearance in that top gap. I have seen 3/16" as a minimum, but don't know how general a spec this is.

It may also be worth watching the motor under load, as a mount may show itself as one corner of the engine flops around...which is all relative with a diesel .


-David
Independence 31
Emerald

And finally...

All of these suggestions truly must be investigated-especially watching the engine mounts while operating under load. The ONE thing I CAN add is that the prop may be out of balance-and any prop shop can help with this..
Either way, you have some homework to do, but rest assured this can and should be corrected!!@

Seeya,
S

more on mounts

I once saw a boat with a stripped motor mount. It would tighten but wouldn't stay that way. Tricky. So I also suggest to check the mount bolts and make sure that they actually hold some torque. You can do that without actually turning them and changing the mounting.

After the bacteria warning was lifted on the Chesapeake last month, I dove our prop. I found a lot of barnacles grown since April. In our case it was vibrating a little as Paul (Shadowfax) suggests, but mostly the revs started dropping. From the amount of growth it wouldn't surprise me if it vibrated a lot.

That reminds me, I ordered a Brownie pressurized snorkel right after I cleaned the prop and it's still on backorder !

All good!

Thanks for the input. I suspect that there's a little of all of this in my problem. Last October I had to have a diver go under the boat to chip away the propcrud before I could motor over to my winter storage yard. The boat simply would not go faster than about two knots. The prop (which, by the way is cleaned every two weeks during the warmer months) had become encrusted with so much barnacular sea life it almost looked like a stuffed toy version of a folding prop.

Thanks...

Steve

Over time folding props wear and will vibrate more and more. Martek will rebuild their props and I think its pretty reasonable. What happens is the blades end wobbling at certain speeds.