Kubota L4740 Engine "knock" Help?

[crazyal]

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.

 

[dodge man]

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]

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.

 

[jshwhite]

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.

 

[TMGT]

Re: Kubota L4740 Engine "knock" Help?

Well whatever it is, I'm sorry for your problems but looking forward to what the exploration finds.

 

[jshwhite]

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...

 

[crazyal]

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]

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.

 

[dodge man]

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.

 

[jshwhite]

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.