D2 3J donkey engine

Great question - when I did both of mine (5U and 3J pony engines), I didn't think about the seal size so I'm glad you pulled up this question. Mine are 030 I think but they don't leak and have the standard Cat part # seals in them

Hmm interesting, i will definitely make a note of that.
Hopefully someone on this group will be able to shed more light on the topic

Are the U donkeys any different to the J donkeys? Obviously things like electric start

Thanks great info to know

Thanks great info to know

Exact same basic donkey motor, just subtle changes to the bolt on stuff like upper manifold and heads over the years and models, none of the Parts Number books lists a seal for undersize cranks to go with the undersize bearings, so I assume Cat didn't think it necessary.

If you were running the pilot motor 8 hours a day I'd be concerned, but generally they are lucky to run 15 minutes max, most times 5 minutes, can't figure much oil could be lost in that time past the seals.

I agree Mike. I have not put any oil in my ponies since the initial set of runs after rebuilding (first start, flush, couple of runs, another flush and done) and they're about halfway down the stick. I can't see any leakage on the flywheel end seal. Who knows about the other end but the pinion chamber has not gone up at least.