I picked up this 1937 RD4 and she runs and operates fine other than a steady small stream of oil leaking out of the rear engine seal. My question is what kind of seal (if any) is on the crankshaft it’s self. I’ve read that some older machines just have threads cut into the crank to keep pushing oil back in, would an RD4 be like that or will it have a rope seal? I have the shop manual and parts book for the machine but can’t find any details on what I want to know. It only shows “packing” that looks like it seals the rear main bearing cap to the block, if this packing is bad would it let a steady stream of engine oil run out?  If anyone has any information or pictures of the rear seal of an engine that would be great! Also if anyone knows a part# for an oil filter off the top of their head that would be great!  Thanks, wylee 

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I've never had one of these engines apart but on most of the older Cat engines there's no seal only a reverse Buttress thread that pushed the oil back into a drain hole that goes back into the crankcase. You may want to check and see if the breather on the right side of the engine is clean. Could be too much crankcase pressure.

Thanks, I’m new to the forum and did find the search bar and the other posts. I’ve never tore apart any old diesel engines before, I mostly have gas v8 experience. This is my first dozer project. I checked the breather and it’s clean. If the drain hole is plugged would it cause a substantial oil leak? I can only run the machine for an hour or so before I need to add more oil. Is it possible to leak that much if the packing between the main cap and the block is shot?

Perhaps the main bearings are worn beyond spec and allowing too much oil for the reverse thread too handle.