Kubota L4740 Engine "knock" Help?

[TMGT]

Re: Kubota L4740 Engine "knock" Help?

If they offer an oversized bearing you should be good then, that'll greatly simplify the repair, and reduce the cost!
Definitely agree about the oil shortage, now the real question is why?

 

[pmsmechanic]

Re: Kubota L4740 Engine "knock" Help?

If they offer an oversized bearing you should be good then, that'll greatly simplify the repair, and reduce the cost!
Definitely agree about the oil shortage, now the real question is why?

Either the front oil passage is blocked/partially blocked or someone sat the tractor on it's tail with the engine left running.

 

[TMGT]

Blockage would be my first guess also, depending on how the oil is fed it could be some other things.

Just like to find root cause so history doesn't repeat!

 

[jonsstihl]

sorry to see that. looks like a bunch of casting flash to me but I have no first hand experience rebuilding engines.

 

[Hilbilly]

Very interesting thread and thanks for taking the time to document your journey and taking pics. Not really something a guy wants to do when he's dealing with problems.

Sure glad you have the skills to do this yourself.

 

[Gregster613]

I second all that Hilbilly said! Very informative and well documented thread. I'm glad that you have the skills. space, and equipment to do this yourself; saves you mucho $$ on labor. Great job.

 

[crazyal]

Really makes you think about getting Kubota insurance when you buy a used tractor. It could have been just bad timing or it could have been the previous owner knew something was wrong (or he did something wrong) and sold it to avoid a big repair bill.

 

[jshwhite]

Blockage would be my first guess also, depending on how the oil is fed it could be some other things.

Just like to find root cause so history doesn't repeat!

Agree completely. Definitely will clean/check every oil passage. Also replace oil pump and pickup.

Very interesting thread and thanks for taking the time to document your journey and taking pics. Not really something a guy wants to do when he's dealing with problems.

Sure glad you have the skills to do this yourself.

I guess misery loves company Sure is nice to bounce ideas around and get other thoughts.

Not sure about the skill level, but I'm always up to learning something new. It's what you have to do when you don't have a bunch of money to throw at it. Necessity makes a great teacher...

Really makes you think about getting Kubota insurance when you buy a used tractor. It could have been just bad timing or it could have been the previous owner knew something was wrong (or he did something wrong) and sold it to avoid a big repair bill.

I really do wonder if the previous owner knew something. Especially since he sold it at a really good price. I thought I was just getting a good deal, but I guess you get what you pay for.


So I talked to the Kubota service department and their recommended machine shop today. I misunderstood originally. They do NOT offer oversize bearings - undersize for turning the crank, yes, but not oversize if you need to bore the block. And since there's no cap on that end, there's no way to clip the cap and line bore it. The machinist looked at it and thought it might actually not be too bad and you might get away with just putting a new bearing in it. But obviously the official recommendation from them and the dealer is a new block - $$$

So I took it and showed it to a friend of mine who is one of the best engine rebuilders in this part of the state. He's got lots of experience and is a bit of a legend around here in building racing engines. He's also good at coming up with innovative solutions He said he thinks I very well could get away with just replacing the bearing. Yes the block is scored, but since it's pressed in it might hold.

So I ordered the bearing and will see how it fits. If it's too loose, he said there is a possibility of boring it very oversize and fitting a steel bushing, then the bearing inside that. At this point I'm open to any of that, as the block is junk otherwise.

Considering that a new block is $3500, I'm game just go with a new bearing, provided it's reasonably tight. Worst thing that could happen is I end up right back where I am now.

One other thought I did have: what about finding an aftermarket oversized bearing? Surely there's a company out there somewhere who offers stuff like that. Anyone know anything about that?

 

[pmsmechanic]

It wouldn't cost $3500 to have the block bored and a steel sleeve pushed in. Also if the new bearing is reasonably tight and in alignment with the other bearings a little JB Weld would go a long ways towards keeping the new bearing in place.

If anyone doubts the effectiveness of JB Weld my friend tells of how they would glue broken cylinder liners together on Detroit diesels in the 70's to keep them running till new parts came. And the liners were broken through the windows in the liner that the intake air entered the cylinder through. I would think that would be a harsher environment then just helping keep a bearing in place.

 

[Alien]

I remember we used to get bearings metal sprayed to make them tight. Long time ago. You could also get crankshaft journals metal sprayed and re-ground too.

 

[TMGT]

Re: Kubota L4740 Engine "knock" Help?

Check in the Items For Sale section, member Harry in Ky was parting out a V2403 that has spun a rod bearing from being low on oil, block might be good though. Said he was scrapping it in a few weeks so might be gone already but worth a try.

Can't remember but thought the L4740 used the V2403

 

[jshwhite]

I love the old time solutions! These days they just throw new parts at it and don't bother with the effort to fix it.

I wouldn't have thought of JB weld, but that's a good idea. I guess as long as you were careful not to get it in the oil channel, it wouldn't hurt.

Alien, I'd never heard of metal spraying before. Looked it up on YouTube. Quite interesting!

 

[crazyal]

From what I understood, maybe this is an old thing now, is that to get the gap between the rod and crank correct you just file the end of the rod down. When the ends meet while tightening up the bolts the bearing ends meet and compress the bearing which makes it thicker. Maybe now to make things simple and because the machining process is much tighter the bearings just fit.

I talked with a local machine shop years ago about connecting rods that spin bearings. Obviously a rod can be replaced easier but in some cases they would recondition them by shaving a few thous off of the cap and then reboaring the rod. One of the other things they would do is use a thicker bearing. There's nothing magical about them. If it's designed for a larger diameter (which is what you want) they just shaved the end off and bent it to match the crank. As long as it fit tight, it was the right width, it had the oil passage hole in the correct spot, and the gap between it and the crank was correct it would work. It's more messing around on the mechanic's end vs just putting in the correct size but it can be done. I suspect that if this is correct it would work with a main as well.

Did anyone actually measure it to see how much larger it is compared to the other mains?

 

[ericm979]

Instead of JB weld you could use one of the LocTite products made specifically for filling in gaps between parts that are supposed to be a press fit.

 

[TMGT]

From what I understood, maybe this is an old thing now, is that to get the gap between the rod and crank correct you just file the end of the rod down. When the ends meet while tightening up the bolts the bearing ends meet and compress the bearing which makes it thicker. Maybe now to make things simple and because the machining process is much tighter the bearings just fit.

I talked with a local machine shop years ago about connecting rods that spin bearings. Obviously a rod can be replaced easier but in some cases they would recondition them by shaving a few thous off of the cap and then reboaring the rod. One of the other things they would do is use a thicker bearing. There's nothing magical about them. If it's designed for a larger diameter (which is what you want) they just shaved the end off and bent it to match the crank. As long as it fit tight, it was the right width, it had the oil passage hole in the correct spot, and the gap between it and the crank was correct it would work. It's more messing around on the mechanic's end vs just putting in the correct size but it can be done. I suspect that if this is correct it would work with a main as well.

Did anyone actually measure it to see how much larger it is compared to the other mains?

For all the other bearings this would work, however this happens to the the 1 bearing that does not use a split bore.

A lot of manufacturing has gone to a cracked cap design for the connecting rod big ends, this requires boring and oversized bearings since the mating surfaces the rods big end cannot be ground down.

 

[TMGT]

Re: Kubota L4740 Engine "knock" Help?

Instead of JB weld you could use one of the LocTite products made specifically for filling in gaps between parts that are supposed to be a press fit.

Loctite 640 sleeve retainer is what I'd probably use for this, use it regularly but never tried it on a main bearing. Depends on how lose the tolerances are.

 

[pmsmechanic]

Re: Kubota L4740 Engine "knock" Help?

Loctite 640 sleeve retainer is what I'd probably use for this, use it regularly but never tried it on a main bearing. Depends on how lose the tolerances are.

And it depends on if it can handle the heat in that environment. If it can it's also a good choice.

 

[TMGT]

Re: Kubota L4740 Engine "knock" Help?

And it depends on if it can handle the heat in that environment. If it can it's also a good choice.

-65 to 400F, should be good, the only worry I have is the pounding a main bearing can take on a diesel.

If the fit is too lose I wouldn't trust anything other then boring and sleeving back to size.

 

[TMGT]

Although I would see if that one used block is still available first!

 

[pmsmechanic]

Re: Kubota L4740 Engine "knock" Help?

-65 to 400F, should be good, the only worry I have is the pounding a main bearing can take on a diesel.

If the fit is too lose I wouldn't trust anything other then boring and sleeving back to size.

I'm with you on a different block and I'm with you on the above quoted text also. I don't think the pounding is any different on a gas or a diesel. Engineers size the bearings to take the load.