Thanks for all your help Brian, just one more question. Can I hone the cylinders without removing the engine? I haven't done this before, and my instinct would say all the crap I knock off the cylinder walls would fall deeper into the engine. How would I go about preventing this...if it's even possible. Maybe I'm just being stupid because I haven't done this yet and am forgetting something. Thanks again!
Kubta b7100 engine removal
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brain55
Veteran Member
If by honing, you mean clean-up the cylinder walls and deglaze them. Then, yes you can. If by honing you mean correcting out-of-round, or taper, or open them up for oversize pistons. Then, no you can't.
There is not that much "crap" to worry about. You have the pan off anyway. I go through several cans of Brakleen getting all of the residue from honing off of the cylinder walls, crankshaft, and crankcase. I know some will say that the honing grit will get down into the main bearings. I haven't seen this happen or if it did it never was enough to significantly reduce the life of the crank or bearings. By doing an "in frame" rebuild like this, you are cutting corners anyway. Will you get several more years of operation out of the machine? More than likely, but there is no guarantee. If you are looking for 6000 hours or more of operation, the correct way would be to completely disassemble the engine and have a machine shop bore it.
Brian
By the way, if I was doing this I would take the head apart and inspect the valves. Many times you can get away with just lapping the valves. But if you don't check the head out, and just put it back on, then you might have just wasted your time doing a ring job.
Alright, I'll make sure to check the head out too, valves and all. And yes, I was only planning to do a quick deglazing, basically a polish. I know it won't be perfect by the time it's done, but hey, it's blowing a ton of oil now, so a few little things might go a loongg way. I just want to stop that dreaded blue smoke at idle and under load. I don't have time or money to do a crazy ground up rebuild at this time, and this is basically an educational project to get a good working tractor that'll last me a while. Basically a simple restoration. Thanks again for all your help.
czechsonofagun
Elite Member
Don't you think that engine swap would be cheaper and better solution in a long term? It would save you work, time and profesionally remanufactured engine should last several thousand hours.
Another vote for a swap, even a high hour in fair condition. If the cylinders are out of round and tapered deglazing is a waste of parts. Same for the valve guides and stems, that could be the source of the oil leak. Changing rod bearings but not cam and mains without knowing clearance could leave the rods oil starved.
You could put a few hundred dollars into this and end up with more problems than you started with.
You could put a few hundred dollars into this and end up with more problems than you started with.
brain55
Veteran Member
Do you have a source for a remanufactured engine for this machine with pricing? If you do, I would love to have it for future reference.
Having done this several times for people that could not justify the cost of a full rebuild, it works out fine. Yes there is a line where it shouldn't be done. If the engine was severely dusted or has many hours on it then yes it could be a waste of parts. But with a slight taper or out of round he will get many more hours of operation out of it before it has to be done properly. I think for a guy doing the work himself it is worth the $500 risk. I agree that the head needs to be looked at and repaired as needed. As far as cam and main bearings, first of all this engine doesn't have cam bearings, secondly Kubota's nearly never have bearing issues at all. In 23 years of working on primarily Kubota equipment or equipment with Kubota engines, I have seen one bearing failure.
Brian
petes
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I agree with Brain55. Although I opted for a swap (marine generator D950 into my B7100) because my $500 tractor came with a cracked head and I lost patience trying to find a head for what I though to be a reasonable cost), I first started checking out the guts of my D750 in prep for a rebuild. ~1750hrs, air and fuel filters looked like they'd maybe never been changed. Cylinders liners were worn and stepped, the middle liner pitted and piston damaged from a cracked/leaking head. Despite the abuse when I tore into the bottom end found the bearings and journals in perfect condition. Plastigauge'd right in spec, no scoring or wear. Buttoned it back up fully intending to put in liners, pistons, rings and a valve-jobbed head if I could find it.
Oh, and to the original question... just split the tractor and get the engine on a stand. You can't "get the engine out" without splitting since the engine block is what holds the front and rear of the tractor together. Although it sounds daunting, it's not hard at all and does not require any special skills or tools. The 2-4 or so extra hours to clean, remove the loader and subframe, split the tractor and put it all back will be well worth the improved access and ability to really check things out and work clean, plus you'll be able to get a look at the clutch while it's split. If just pulling the head to do valves of a gasket, I'd definitely do it in frame, but if you want to pull the pan and have a look at anything, especially removing pistons/honing looking at bearings, etc. you'd be cursing the limited access and dirt. You'll be glad to have the engine by itself on a stand or bench.
Oh, and to the original question... just split the tractor and get the engine on a stand. You can't "get the engine out" without splitting since the engine block is what holds the front and rear of the tractor together. Although it sounds daunting, it's not hard at all and does not require any special skills or tools. The 2-4 or so extra hours to clean, remove the loader and subframe, split the tractor and put it all back will be well worth the improved access and ability to really check things out and work clean, plus you'll be able to get a look at the clutch while it's split. If just pulling the head to do valves of a gasket, I'd definitely do it in frame, but if you want to pull the pan and have a look at anything, especially removing pistons/honing looking at bearings, etc. you'd be cursing the limited access and dirt. You'll be glad to have the engine by itself on a stand or bench.