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.
OP
jshwhite
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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
OP
jshwhite
Gold Member
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
crazyal
Super Member
One thing you can do is get some plastic gauge. Unbolt the connecting rod caps one at a time, look for damage to the bearing and crankshaft. Then follow the directions that come with the plastic gauge to determine if the clearance is within specs. That'll tell you a lot better than "it doesn't feel loose". If you find a bad bearing on a connecting rod but the crank shaft doesn't look bad (since you may have caught it early enough) you may get away with just replacing the bearings.
I think you said you weren't the original owner. It's likely that if you are not that the person who was just started it up after it had been sitting and put a load on the engine without allowing the engine the time it needed. Or maybe they just left the throttle at PTO speed and started it that way.
I think you said you weren't the original owner. It's likely that if you are not that the person who was just started it up after it had been sitting and put a load on the engine without allowing the engine the time it needed. Or maybe they just left the throttle at PTO speed and started it that way.
dodge man
Super Star Member
At this point, the engine has to come out. In my opinion there is no doubt. The metal? I’m with you, I would lean towards a broken piston and/or rings. Just thinking out loud, what has gear teeth? The cam and oil pump? I would think if they had lost a lot of metal it wouldn’t run. Good luck!
TMGT
Elite Member
Is there excessive smoke or loss of power? I was thinking the same thing about piston rings but,, If there is piston ring material in the oil pan it would most likely be the oil control ring which would show up with oil smoke. if its the compression ring then there would be major piston failure and would most likely be noticeable power loss and smoking not to mention oil dilution from the fuel and excessive crankcase pressure.
As for the gears, there are 5 in the drive system on the front of the engine. It would be pretty rare, but i have seen gears with broken teeth knock. The only reason I mentioned it was because a few of the magnetic shards look like the helical gear teeth used, but they are hard to see in the pictures.
As for the gears, there are 5 in the drive system on the front of the engine. It would be pretty rare, but i have seen gears with broken teeth knock. The only reason I mentioned it was because a few of the magnetic shards look like the helical gear teeth used, but they are hard to see in the pictures.
OP
jshwhite
Gold Member
Went to the Kubota dealer and talked with the service manager. He said not a chance on warranty - too old and I'm the second owner.
I brought along some of the metal pieces. As soon as he saw the aluminum shards he said, "Those are rod bearings." Then I showed him the other pieces. He said there are no gears in there small enough for those pieces to be gear teeth. He thought it could be a ring, but wasn't entirely sure. He said it might be possible that the aluminum is from a piston but he really thinks it's rod bearings.
TGMT, no there was not excessive smoke. And power seems fine to me.
Long and short of it is that I'll be splitting the case this afternoon and pull the motor. Sooner or later the problem should be obvious.
I brought along some of the metal pieces. As soon as he saw the aluminum shards he said, "Those are rod bearings." Then I showed him the other pieces. He said there are no gears in there small enough for those pieces to be gear teeth. He thought it could be a ring, but wasn't entirely sure. He said it might be possible that the aluminum is from a piston but he really thinks it's rod bearings.
TGMT, no there was not excessive smoke. And power seems fine to me.
Long and short of it is that I'll be splitting the case this afternoon and pull the motor. Sooner or later the problem should be obvious.
OP
jshwhite
Gold Member
Well, we've found the problem.
Those metal bits were teeth from the oil pump gear, and a few on the crank gear. See pics.
The aluminum shards were the front crank bearing. See pic. It was completely loose. I just pulled it out with a pair of needlenose.
Remember back earlier in this thread I said I thought the crank pulley was vibrating? That's exactly what was happening. And that's why I had to replace the front crank seal.
My theory is that the bearing went bad, which caused the crank to start wobbling, which then damaged the gears. Not sure why the bearing went bad after only 350 hrs...
To me this also explains the knock that wasn't "typical". Every time that front cylinder fired, it applied extra pressure on the crank and knocked that loose bearing around. Also the crank gear teeth are only broken in one spot, so that likely added to the knock.
So next up is to pull the crank and see what kind of damage I have on the shaft.
Thoughts, ideas, recommendations welcome...
Those metal bits were teeth from the oil pump gear, and a few on the crank gear. See pics.
The aluminum shards were the front crank bearing. See pic. It was completely loose. I just pulled it out with a pair of needlenose.
Remember back earlier in this thread I said I thought the crank pulley was vibrating? That's exactly what was happening. And that's why I had to replace the front crank seal.
My theory is that the bearing went bad, which caused the crank to start wobbling, which then damaged the gears. Not sure why the bearing went bad after only 350 hrs...
To me this also explains the knock that wasn't "typical". Every time that front cylinder fired, it applied extra pressure on the crank and knocked that loose bearing around. Also the crank gear teeth are only broken in one spot, so that likely added to the knock.
So next up is to pull the crank and see what kind of damage I have on the shaft.
Thoughts, ideas, recommendations welcome...
crazyal
Super Member
My guess is the oil gallery leading to that front bearing is plugged. You may find that the rod on the #1 cylinder is also fed by that port and has some damage. The good news is that your engine may need a limited number of new parts. Things like the rods and pistons should be fine. I would tear it all the way down and have the block cleaned and then verify that all the oil galleries aren't restricted. Hopefully any plugs that were applied after machining the block can be removed and reinstalled. I know they make brushes for cleaning them out. A bore scope might be worthwhile to check them out.
TMGT
Elite Member
Unfortunately that front bearing spun, most likely the block will need to have that bearing bore oversized (if an oversize bearing is available) or bored and sleeved back to size.
Depending on what other damage there is, a reman short block or used takeout might be in order.
Of course, it had to be the one bearing bore that is integral to the block.
Depending on what other damage there is, a reman short block or used takeout might be in order.
Of course, it had to be the one bearing bore that is integral to the block.
dodge man
Super Star Member
I would say that is an unusual failure. Hard to say what caused it. Factory defect? Abuse from previous owner? Low oil level? I think low oil level usually hit bearing further away though, like a back cam bearing. If the previous owner didn’t abuse or neglect it, probably factory defect.
OP
jshwhite
Gold Member
I got the engine tore down completely. The crank actually looks in pretty good shape, but the block is scored bad. See picture. Definitely will need bored.
The left balancer shaft front bearing was also very worn. Not completely spun, but the inside, and the shaft was scored. See pic. Since that's right beside the crank, I'm guessing it's the same oil supply passage? At least that's the theory I'm developing...
Rod bearings on cylinder #1 and 2 also a bit scored, but not bad. Just replacement should be fine on those. Also main crank bearing #2.
Long and short of it is I think at one point there was a significant oil shortage to the front of the engine. Some parts got hit worse than others.
Tomorrow I'll have a chat with the service guy at the Kubota dealer - he's very helpful. He also recommended what he said is "the best" machine shop in the area that he said they send all their work to. So I'll know more tomorrow. I do know Kubota offers oversize bearings, so hopefully that will be enough to fit with needing to bore the block.
The left balancer shaft front bearing was also very worn. Not completely spun, but the inside, and the shaft was scored. See pic. Since that's right beside the crank, I'm guessing it's the same oil supply passage? At least that's the theory I'm developing...
Rod bearings on cylinder #1 and 2 also a bit scored, but not bad. Just replacement should be fine on those. Also main crank bearing #2.
Long and short of it is I think at one point there was a significant oil shortage to the front of the engine. Some parts got hit worse than others.
Tomorrow I'll have a chat with the service guy at the Kubota dealer - he's very helpful. He also recommended what he said is "the best" machine shop in the area that he said they send all their work to. So I'll know more tomorrow. I do know Kubota offers oversize bearings, so hopefully that will be enough to fit with needing to bore the block.
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