Have I trashed my genny?

Nick_H

Nick_H

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www.ybw-boatsforsale.com
The genny has been worked pretty hard for the last few weeks. Yesterday I noticed an unusual vibration, so switched it off and it spat a load of oil or soot out the exhaust. Water was a bit choppy so it dispersed quickly, so couldn't say for sure if it was oil or soot, but it looked more like soot. Oil was a bit overfilled at last service, has done maybe 200 hrs since, and is still over full so haven't been losing oil in any great qty. Any ideas?
 
what's the make pls ? Water or air cooled ?

It's not unknown for exhausts to coke up especially if dirty fuel is used or an injector is off-song.

Vibration ? Could be overload, water in the fuel, duff injector, valve problem, injector pump.....


Ejection of soot ? Vibration could have shaken loose carbon from the exhaust manifold or silencer.



Overfill ? hmm, does it normally use up oil ? It can be dangerous especially if the genny is operated in rough weather, as engine oil may get past the valves and start an runaway acceleration..
 
Last edited:
sarabande said:
Overfill ? hmm, does it normally use up oil ? It can be dangerous especially if the genny is operated in rough weather, as engine oil may get past the valves and start an runaway acceleration..
Click to expand...


I would drain out any excess oil, overfilling a diesel engine is a dangerous thing to do. In the past 20 years I have seen first hand 3 diesel engines in runaway acceleration as explained by sarabande. To see someone with ignition keys in hand not quite comprehending why their engine is still running & their cars engine revs gradually increasing and increasing and not being able to stop it is rather disturbing and it ends with a massive cloud of smoke, a lot of noise and then the engine blowing up..
 
Hi Nick, as its a 4 cylinder from memory and its vibrating, there must be some crankcase compression as its spat out oil from the breather hose, it may have blow some piston rings on 1 cylinder and now the vibration is uneven running as the remaining 3 cylinders are having to do the work of 4, which under heavy load wont work, the revs and voltage will drop, that will cause damage to the windings on the alternator too.

If you want to play about and try and diagnose which cylinder may be faulty run it under slight load say immersion and 1 AC unit on then slacken off each injector pipe in turn 1 flat of the pipe nut, fuel will spit out, if there is no engine tone difference on any of the unions then its that cylinder thats not firing, you could have a seized injector nozzle, which in turn will neat fuel the cylinder washing off the oil causing the rings to fail, I have just stripped a kubota based genset to find I could see the gungeon pin through the top of the piston! all caused by a faulty injector nozzle.
 
Hi Nick,

I do not think the overfilling with oil will have caused the vibration issue, Onan genset's are designed to be used underway in motor & sailing boats. the sump is designed so that the genset can operate @ 30 degrees in any orientation, there is plenty of spare room in the sump. plus you have done 200hrs, if there was a problem. you would have seen it before now.

You will see a small amount of soot discharge though the exhaust gas water seperator (if fitted) any way though natural combuston process. this can build up on the inside of the exhaust system and be discharged ever now and then.The soot can be worse if the genset has been overloaded. If it was oil that was discharged you would normally see the oil sheen on the water and or a mark on the hull of the boat.

The Kubota eninges used in these gensets are normally very roburst, I would check all the levels, open the mains AC circuit breaker (so not powering the boat) and start the genset. If there is a problem? you should hear it straight away. you should also check the output voltage at this point. if it's OK you can close the circuit breaker and add some load.

Regards Anthony
 
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