Rear engine oil seal on Gas 50

I don,t have any experience with a 50 engine but take the diesel engines say before the middle 1950s Cat had threads on the rear main crank journal and the bearing was engineered so the oil tended to be screwed back into the bearing and drained back down into the pan.There was no other sealing done on the rear bearing and area other than that. Later engines had a different setup,some with a lip seal and some with a metal ring like a piston ring and parts to be part of it,s function.

SJ is exactly correct. This type of seal was called a non-positive seal. Bearing clearance was fairly critical in them working as designed. These types of seals did not like any amount of crank case pressure.

The thread is called a ''BUTTRESS'' thread. Make sure the drain hole is clear.

Behind the flywheel is a cover plate held on by 6or10 3/8" bolts can't remember it has a felt seal that helps direct the oil back into the crank case. this is the hole that you remove the crankshaft through if so needed (alot of work😊 ) as long as the drain back hole is good and clear you should be all right.

I made sure the return passage was clear. I must have some getting past somewhere. The cap has a groove on the OD to pack with something. I used some graphite but may need some cork. This is between the insert and the block casting. Thanks for the info. I assume it is engine oil comeing out of the bell housing.

Thanks
John