Kubota L4740 Engine "knock" Help?

[dodge man]

I wish I could help more but my reaction is you are delaying the inevitable. Just pull the engine, crack it open and figure it out.

 

[tbk5]

To the OP, I am sorry for your troubles. But, tbis is one of the most informative threads I have read in a long time. Kudos to all responding and TBN

 

[sixdogs]

To the OP, I am sorry for your troubles. But, tbis is one of the most informative threads I have read in a long time. Kudos to all responding and TBN

Very true and what a great thread. I sure hope this has an easy solution.

 

[Tx Jim]

jshwhite
Someone may have already suggested this but have you loosened the inj lines 1 at a time with engine running to determine if knock can be isolated to a certain cylinder? If knock can be isolated to a cylinder I strongly suggest to have that injector or even all injectors pop-off pressure tested.

 

[jshwhite]

If you load the motor and the knock gets lighter, it most likely will be a rod.

Thanks for that info. I did try that and I think it's slightly lighter under load, but not a big difference. Not sure how much difference it should be.

I want to think on that... What I'm trying to do is picture how that fits with no overt change in the knock when you disabled each injector.
And so far I can't reconcile the no change and the no injection. I was just so sure that would at least point to the correct cylinder even if it didn't tell us the cause.

A good way to trouble shoot the difficult ones is to divide up the problem. One problem is we don't know which cylinder, the other problem is we don't know why the knock is happening in that cylinder. We ought to be able to at least get it down to the proper cylinder.

Er, I'm assuming that your spectrum analysis is pointing towards one cylinder. Do you agree with that?

Could it even be something crazy? ....like a dangling glow plug end?

I would have thought disabling the injector would identify it also. No such luck though. But yes the audio certainly is pointing to one cylinder. But I think we knew that already.

I wish I could help more but my reaction is you are delaying the inevitable. Just pull the engine, crack it open and figure it out.

Yeah, I know. I was actually thinking the same. Just hate to do that and find out I didn't have to.

To the OP, I am sorry for your troubles. But, tbis is one of the most informative threads I have read in a long time. Kudos to all responding and TBN

That's what I love about TBN. Lots of helpful and experienced folk on here. I've helped a few people, but I think I've received a lot more help than I've given.

jshwhite
Someone may have already suggested this but have you loosened the inj lines 1 at a time with engine running to determine if knock can be isolated to a certain cylinder? If knock can be isolated to a cylinder I strongly suggest to have that injector or even all injectors pop-off pressure tested.

Yep, been there done that. All it does is drop the RPM, but the knock stays the same.

How many hours does it have on the oil? I think I would change it and send a sample to a lab to have it analyzed. If it is a main or rod bearing that'll tell you.

Yep, that's what I'm doing. It's got a bit under 100 hrs on the oil. Probably not enough to tell in an analysis, but I'm sending a sample off this morning and will see what I get back.

Thanks again everyone. Going to put this on hold for the moment while I wait on the oil analysis results.

 

[jshwhite]

Update: I got the oil sample results back. High aluminum levels, indicating a bearing. They said of course aluminum could be piston, but chrome (rings) and iron (cylinder liners) levels are normal, so most likely a bearing. Rod bearing of course being most likely, although could be a main crank bearing I suppose.

Busy this week, but I'll tear into the engine next week and see what I find.

 

[K5lwq]

Thanks for the update. I would definitely fix this one. Still a very nice tractor. Good luck!

 

[TMGT]

Well that's not what any of us were hoping to hear.
Makes you wonder what the PO did to cause such an early failure.

 

[goeduck]

This will be very interesting. I hope it is relatively easy to correct, considering. Looking forward to your data/pictures.

 

[jshwhite]

Re: Kubota L4740 Engine "knock" Help?

Ok, finally got some time to start on this project. I dropped the oil pan today and had a look up in it. Do you think I should be able to feel some play by hand on the offending part? I can't seem to get any movement other than side-to-side for each rod end.

There were several metal shards stuck in the pickup screen. And a lot more in the bottom of the pan. See picture. Seems that should give a clue?

Those of you with more experience in this, what do you think? Is there some way I should be able to identify the issue from the oil pan, or should I just bite the bullet and tear into the engine?