ONAN generator vibration

[capta]

My Onan 8 kw mkdk with the Kuboda 3 cylinder engine has developed a vibration. This vibration is so severe that it has broken hose barbs, some of the metal fuel lines (which I replaced with hose) and the bracket for the fuel filter, but it is just barely noticeable to me. This developed so slowly that it wasn't until the metal bits began to break that I realized I had a problem.
The engine starts in seconds, runs like a top, doesn't burn oil, doesn't have excessive crankcase pressure and I can find absolutely no reason for this vibration. The vibration does not change with the load on the generator, but it can be felt throughout the boat's floors and creates some rattles.
We must run it 2.5 to 4 hours a day for our refrigeration, so it's not like I can take it off line to do some trial and error stuff.
Any thoughts would be appreciated as I am completely clueless on this one.

 

[kappykaplan]

Motor mounts?

 

[Chris Patterson]

Does this engine have a harmonic balancer? That would be my first go to.

 

[kloudie1]

Check all valve clearances before going further..
Could be a bad injector too.. I don't think that engine has a compression release, so you can troubleshoot by starting the engine, then wrapping a rag (to catch the fuel) around the fuel inlet connection for an injector and loosening it until the fuel comes out and that cylinder is neutered. Do all three.. if one doesn't make a difference then that cylinder is the problem..could be several things in that cylinder, but an injector would be a good start point.

 

[capta]

Thanks guys, I appreciate the input.
When I get to Trinidad I hope to find an injector shop, because that was my thought too. But since the gene runs fine under load????
We'll see.

 

[Benny17441]

KappyKaplan mentioned the motor mounts and I would like to expand on them as it seems a very likely candidate for what you are experiencing. All engines have a natural vibration but that is kept in check by the motor mounts. Your boat is 30+ years old and if the generator is original equipment those mounts should by now be soft at best. They work in a harsh environment with oil, diesel fuel, heat, humidity and fumes. Upon visual inspection they might look new but they can cracked or soft. Motor mounts do not cause vibration and some of the possible causes for increased vibration are mentined by Kloudie but motor mounts do reduce vibration when they are in good shape. I agree do check the valve lash on the engine as incorrect setting can be a major cause of vibration. Dirty injectors can also add to the problem but my point is if the motor mounts are original eqipment go ahead and replace them.