L4740 HST Engine knock

Husaberger · Oct 11, 2016

Was just about to do some trenching when engine started to knock
Tractor has about 250 hours with routine service
Kubota knock - YouTube
All informed opinions welcome

kuboman · Oct 12, 2016

Sounds like a complete misfire on one cylinder. Either an injector or delivery valve. Loosen the nut on the top of each injector one at a time. The one that is dead will be the one with no change in the sound of the engine.

Husaberger · Oct 12, 2016

Thanks Kuboman
What do you suggest once I isolate the faulty cylinder?

kuboman · Oct 12, 2016

Husaberger said:
Thanks Kuboman
What do you suggest once I isolate the faulty cylinder?

Injection systems are usually very reliable and usually fail because of contaminated fuel. Make sure your fuel is clear of dirt and water. Once you determine which cylinder is dead you can pull that injector and have it tested/repaired or you can switch it with a different cylinder to confirm it is an injector or it may be the delivery valve.

Husaberger · Oct 12, 2016

makes sense
will try that tonight and post results
thank you!

MrFoPow · Oct 12, 2016

I hope you guys are right.

Sounds like a spun rod bearing to me.

kuboman · Oct 12, 2016

MrFoPow said:
I hope you guys are right.

Sounds like a spun rod bearing to me.

Certainly sounds like a miss but there maybe more going on.

Husaberger · Oct 13, 2016

Ok. Performed the test suggested by Kuboman
Cracked each injector open and each one altered engine performance/revs dropped (some more than others)

As an aside, I removed the valve cover breather hose to get at the injectors. Is there supposed to be this much smoke coming out of the vent? Kubota knock 3 - YouTube
Not much smoke coming out of the exhaust Kubota knock 2 - YouTube
Aside 2. Fuel filter looked dirtier than I ever remember seeing it
It was changed in January

Opinions?
Recommendations?

SimS · Oct 13, 2016

That #3 video proves to me it's not just an injector. Looks like a ton of blow-by so I would go with rings and/or a broken piston. What does the air filter look like? I ask because the tractor looks pretty dusty/dirty. The engine could also be "sanded" from a dirty air stream. All in all, definitely not good symptoms for such a low hour engine.

SimS