TMGT
Elite Member
Huh, that doesn't really look like bearing material, some peices almost looks like gear teeth?
Kubota L4740 Engine "knock" Help?
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TMGT
Elite Member
Is the material magnetic? You may or may not be able to feel play from grabbing the rod.
Re: Kubota L4740 Engine "knock" Help?
There are two different types of metal. Some I would describe as "pieces" (circled red in photo) are magnetic.
Others are thin "shards" (circled yellow) that are not magnetic.
There are two different types of metal. Some I would describe as "pieces" (circled red in photo) are magnetic.
Others are thin "shards" (circled yellow) that are not magnetic.
pmsmechanic
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You have major internal engine damage. Probably a connecting rod bearing.
TMGT
Elite Member
Re: Kubota L4740 Engine "knock" Help?
How soft are the non-magnetic peices? Do they bend really easy or are they stiff and brittle?
Either way the engine is most likely going to have to come appart, but I'm wondering if the issue isnt under the front cover.
Those magnetic peices look a lot like gear teeth, the non-magnetic could be rod bearing material but don't look like what I'm use to seeing in rod failures.
How soft are the non-magnetic peices? Do they bend really easy or are they stiff and brittle?
Either way the engine is most likely going to have to come appart, but I'm wondering if the issue isnt under the front cover.
Hilbilly
Veteran Member
It's hard to believe a Kubota engine with only 440hrs on it has this kind of major failure. Makes you wonder if the previous owner knew about it.
I feel sorry for you but I'm very glad you have the skills, tools and confidence to tackle something like this. I'm sure dealer costs to trouble shoot and repair this would be very high.
I'm impressed with all the quality help you are getting and the TBN members that are involved.
Wish you good luck in getting the repair completed so you can get back to using the tractor.
I feel sorry for you but I'm very glad you have the skills, tools and confidence to tackle something like this. I'm sure dealer costs to trouble shoot and repair this would be very high.
I'm impressed with all the quality help you are getting and the TBN members that are involved.
Wish you good luck in getting the repair completed so you can get back to using the tractor.
rScotty
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Re: Kubota L4740 Engine "knock" Help?
I'm not surprised you cannot feel anything in the big ends. That's common even with wear. Some people say they can tap the big ends with a light hammer and find wear by the different sounds, but I've never been able to do so.
Looking at those shards, I think you have found your problem..... and the first really hard evidence - other than the noise - that the engine did indeed have to come apart.
I think at this point I would put some time into trying to identify those magnetic shards. I use a 40 power diassecting microscope with top stage lighting. to help identify pieces of parts. Could they be pieces of piston ring? Do the rings on that engine are rectangular cross section or or they the lipped type? I've seen shards like that when a piston land breaks up and the rings get cracked. That happens. I've seen piston land failure and broken rings where I am pretty sure it was manufacturing and not abuse.
Another possibility is the keeper for the piston pin - i.e the small end. There is a land in the piston that retains the wire spring keepers for the small end. I have also seen that fail, and there is just no way that could be due to abuse. When that happens there is no doubt because the cylinder scar is very prominent and is just where you expect it to be: in the fore/aft plane of the engine.
Hmm.... You know, with a bright light you might be able to inspect the cylinders. If it really is a broken ring and land or the piston pin keeper then there should be noticable scars in one of the cylinders.
But having said that about the rings, I would be inclined to go with what TMGT suggested. Right now I'd look up into the cylinders for that scarring, but if I didn't see clear evidence of scarring of the cylinder then before disturbing the big ends I would take off the front cover to look for damage there. And also take a close look at the drives for the oil, hydraulic, and fuel pump. Only when I was pretty sure that none of the shards were coming from the various gear drives would I begin to unbolt the big end to pull the most likely piston.
The good news is that it really did have to come apart, and that now there's no doubt you can find the problem. The ones I hate are the ones where I have everything taken apart, spread out, and measured and STILL cannot find where the problem is.
rScotty
I'm not surprised you cannot feel anything in the big ends. That's common even with wear. Some people say they can tap the big ends with a light hammer and find wear by the different sounds, but I've never been able to do so.
Looking at those shards, I think you have found your problem..... and the first really hard evidence - other than the noise - that the engine did indeed have to come apart.
I think at this point I would put some time into trying to identify those magnetic shards. I use a 40 power diassecting microscope with top stage lighting. to help identify pieces of parts. Could they be pieces of piston ring? Do the rings on that engine are rectangular cross section or or they the lipped type? I've seen shards like that when a piston land breaks up and the rings get cracked. That happens. I've seen piston land failure and broken rings where I am pretty sure it was manufacturing and not abuse.
Another possibility is the keeper for the piston pin - i.e the small end. There is a land in the piston that retains the wire spring keepers for the small end. I have also seen that fail, and there is just no way that could be due to abuse. When that happens there is no doubt because the cylinder scar is very prominent and is just where you expect it to be: in the fore/aft plane of the engine.
Hmm.... You know, with a bright light you might be able to inspect the cylinders. If it really is a broken ring and land or the piston pin keeper then there should be noticable scars in one of the cylinders.
But having said that about the rings, I would be inclined to go with what TMGT suggested. Right now I'd look up into the cylinders for that scarring, but if I didn't see clear evidence of scarring of the cylinder then before disturbing the big ends I would take off the front cover to look for damage there. And also take a close look at the drives for the oil, hydraulic, and fuel pump. Only when I was pretty sure that none of the shards were coming from the various gear drives would I begin to unbolt the big end to pull the most likely piston.
The good news is that it really did have to come apart, and that now there's no doubt you can find the problem. The ones I hate are the ones where I have everything taken apart, spread out, and measured and STILL cannot find where the problem is.
rScotty
Re: Kubota L4740 Engine "knock" Help?
Thanks for the thoughts and help.
Personally I lean toward a piston/ring issue, seeing as the problem was a knock on one cylinder. They do look a bit like gear teeth, but it doesn't seem to me that that would line up with the knock issue. Unless I've actually got two problems here - some gear damaged and a bearing gone bad??
At any rate I'll inspect the cylinder walls as best I can tomorrow and see if there are any clues.
Hillbilly, I'm with you. 440 hrs is way too low for this kind of problem. What do you guys think the chances are of Kubota taking care of this? If I'm not mistaken, the engine warranty is 2000 hrs or 72 months, whichever comes first. So it's 10 years old, but well under 2000hrs. And I'm not the original owner. Worth a try to ask the dealer, do you think?
Thanks for the thoughts and help.
Personally I lean toward a piston/ring issue, seeing as the problem was a knock on one cylinder. They do look a bit like gear teeth, but it doesn't seem to me that that would line up with the knock issue. Unless I've actually got two problems here - some gear damaged and a bearing gone bad??
At any rate I'll inspect the cylinder walls as best I can tomorrow and see if there are any clues.
Hillbilly, I'm with you. 440 hrs is way too low for this kind of problem. What do you guys think the chances are of Kubota taking care of this? If I'm not mistaken, the engine warranty is 2000 hrs or 72 months, whichever comes first. So it's 10 years old, but well under 2000hrs. And I'm not the original owner. Worth a try to ask the dealer, do you think?
rScotty
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Re: Kubota L4740 Engine "knock" Help?
I would take a couple of those magnetic bits and see if you can see any casting granulation - that would be where the part originally broke off of a larger piece. Gear teeth would have any granulation along the long axis, where rings or piston pin keepers would have the granulation at one or both of the ends. Doing this may require magnification.
Two things gone bad? It happens, but I'm a "show me the evidence" kind of guy. So far I don't see any evidence of a bearing failure.
Would Kubota help? They helped me with a hydraulic cylinder after the warranty was up, but that was a matter of less than a year. It could depend on on whether you can get a tech type interested in your problem. From the quality of the work you've done so far I'd say you have a chance.
Unless of course it is piston ring/land failure. That would be damage typical of ether starting fluid & not as interesting.
rScotty
I would take a couple of those magnetic bits and see if you can see any casting granulation - that would be where the part originally broke off of a larger piece. Gear teeth would have any granulation along the long axis, where rings or piston pin keepers would have the granulation at one or both of the ends. Doing this may require magnification.
Two things gone bad? It happens, but I'm a "show me the evidence" kind of guy. So far I don't see any evidence of a bearing failure.
Would Kubota help? They helped me with a hydraulic cylinder after the warranty was up, but that was a matter of less than a year. It could depend on on whether you can get a tech type interested in your problem. From the quality of the work you've done so far I'd say you have a chance.
Unless of course it is piston ring/land failure. That would be damage typical of ether starting fluid & not as interesting.
rScotty
