1942 D4 pony oil leak

[Suomalainen]

Hello to all you Cat guys in this great club. I have a nice starting and nice running starting engine on my 1942 D4 but it leaks engine oil bad into the pinion housing and then out the main clutch compartment. I know that originally it depended only on groves in the crankshaft to keep the oil in being there is no seal there like on the flywheel end. Puzzling is the fact that there is no leak on the flywheel end which would be expected on a worn crankshaft and bearings, and that flywheel end bearing does not feel like it is worn bad.
It seems like there should be some solution other than a complete overhaul of such a good running engine. Does anyone have any ideas like perhaps Cat may have made a field changeover and added a seal on that end later? I though I had a solution by letting the pinion housing just fill up as it worked fine being overfilled but then all of a sudden it really started coming out the bottom of the main clutch. I have had other engines leak oil at the flywheel but still not have this bad leak at this end so it has me wondering. Very likely the previous owner run it low on oil causing destruction of this drive end first but still not show wear at the flywheel end yet.
I really do not think there is any solution other than a complete tear down and rebuild but just am looking for confirmation on my own thoughts.

[ol Grump]

I've never had a pony apart but looking at the Parts Book (Form UE 032504) at the crankshaft assembly, it shows a seal 2B6005 on the drive end between the cam gear and throws on the crank.

[jmvmopar]

I'm not showing a seal on the drive gear end of the crankshaft in my parts book for my 7J. I think your leak is from the drive pinion seal. Seal # 2a3688 which napa shows as NOS 20098. You'll have to loosen the pony and pull it up a little and get the starter clutch/pinion out. Then it looks like you can dissassemble it enough without having to take the starter clutch/pinion shaft out of the assembly.

[Toby Nelson]

The early D4400 pony blocks didn't have a provision for a seal on the gear end of the pony crank. If your pony crankcase can't breathe enough it will push oil into the pinion clutch easier. Once there it can only get into the bellhousing past the pinion shaft seal or the large rubber o-ring type seal that seals the pinion housing to bell housing.

[Old Magnet]

The pinion seal is your most likely candidate. Oil getting past the crankshaft seal (gear end) would be indicated by high oil level in the pinion compartment if the pinion seal was ok. The crankshaft seal (gear end) came on the scene at sn 4G5916.

[Suomalainen]

Thanks for all your advice fellows. It seems Old Magnet got to the point in that there should be a seal at the gear end of the crankshaft the same as there is at the flywheel beginning with serial 4G5916.
Some time ago I had the pony on my RD4 serial 4G5460 open to repair a broken drive gear which caused a bent magneto shaft all due to a loose flywheel, all of which caused me to obtain the machine. Anyway there was no seal in that pony so I thought there would be none in this either and that sure had me puzzled about what to do with an otherwise good engine.
It is sure good to have a group of fellows like you to discuss issues with.
Thank you, Suomalainen (Finlander)

[Haole Cat]

Not sure if this will work for you, but this is what I do.

The same seal on my 3J leaks. I use 1 half oil/ a small amount of seal fix additive. I also use a little Rislone which I swear by in all my engines. This concoction really seems to do the trick. I'm not trying to sell Rislone, but my Grandpa used it, my dad used it and I use it. Good stuff, for worn engine and seals..