Question about which cylinders seem to fail more often.

[texasgeezer]

Last fall I purchased a Kubota L2250DT with the D1302 engine (about 1050 hours). Regrettably believed the old guy 'it's a good tractor'. So far I've put about six hours on it & about $2000 for parts (new & used). Thought it had a slight fuel knock, but turned out to be the #2 (middle/inner) cylinder was starting to fail. Will probably do a complete rebuild bored to the D1402 size.

After hours & hours of research, I'm starting to think that Kubota has or had a problem with their inner cylinders compared to their outer cylinders (probably related to cooling). I'm basing this on the fact that Kubota & other suppliers of piston & rings for the Kubota industrial D1302 D1402 IDI & other engines provide a slightly smaller piston for the inner cylinders. Haven't been able to find how much smaller (one guy said he thought it was about .0005" smaller).

So my question is, for engines that failed due to "piston galling &/or cylinder scoring" which cylinders showed the most damage or wear?

I'm thinking of making my #2 cylinder slightly larger since Kubota doesn't seem to offer a smaller piston for that inner cylinder.

 

[texasgeezer]

Just spoke with another large shop that rebuilds Kubota engines. They said they think the pistons for the IDI engines (that have different part #'s for their pistons) are 'heat treated' not smaller. They also said they have wondered why, but never had a definitive answer.

Does anyone know? Are they smaller or are they heat treated, coated, etc.???

One of the piston suppliers "Karan' in Houston only has pistons for the outer cylinders. Said they are working on getting pistons made for the inner cylinders.

Another supplier 'Reliance parts' has different part #'s for the inner & outer cylinders but didn't know why they are different (at least the person I contacted did not know).

Kubota corporate doesn't seem to want to reply to email requests about information.

 

[texasgeezer]

Additional information about pistons for the D1402 IDI engine. One of the vendors was willing to do a quick comparison of the two pistons. One for cylinder 1 & 3, the other for cylinder # 2. They said the piston for cylinder 2 weighed slightly less & had a shorter skirt length. No comment was made about the diameter.

Does anyone know why there is a difference in pistons used in the same engine?

 

[kuboman]

Never heard of there being diff pistons. As for failing it is usually the back cylinder that fails due to the extra heat. If your #2 went I would blame a bad injector for causing the problem.

 

[texasgeezer]

Stopped at one of the two fairly close Kubota dealers yesterday and asked them about the difference in Kubota pistons for the same engine. He said he had asked 'someone' once before & was told it was the metal formula that was different. Hard to believe that would be the answer. If another formula was better why not use it for all the pistons.

Another comment he made, that continues to make me a believer in Kubota quality, is that in the 8 years he has been there he only recalled two engines needing to be rebuilt. That's pretty impressive. Could be due to their high cost of rebuild though. For my tractor if they did the work it would probably top $5000. I can buy another tractor for close to that price.

 

[texasgeezer]

I'm still researching this, via internet & phone calls.

So far, getting more answers that indicate the inner pistons might be .0005" less in diameter "due to thermal loading/expansion".