I have a 1948 D4 7U serial #1848 that is leaking oil into the hour meter. I can no longer read the numbers and have a couple of questions. I ordered a new seal and mounting gasket from the local Cat dealer. First question: Is the oil shared from the injection pump housing? Next question: Have any of you replaced the seal and is it a difficult job ot does it rquire any special tools?   I have watched Toby's video (Sasquatch) on the repair he did on his D2 but i dont know if things are different with mine. Any help would be appreciated.

Hi,
it is a simple job to renew the drive shaft seal as outlined in any of the Yellow Servicemen's Reference Books for most Cat engines of the day that use this style meter.
The extension housing, or bearing as Cat call it, is a light press fit into the main meter body--grip the extension hsg. in soft jaws in the bench vice and rock the main meter body back and forth in a twisting and pulling out motion and it should separate.
Change the seal with the lip facing the injection pump or drive gear end.
Of particular importance is to locate the oil drain drilling in the extension hsg. to point downwards when the meter is in position on the engine so as drain lube oil between the drive gear and lip seal.

Found a scan of procedure, see below.
Cheers,
Eddie B.

Thanks for your time Eddie B

Great additional information Neil, thanks.

But it is the opposite when filling a carrier roller with grease, when pumping grease in there has to be an escape passage. That is why there is a relief valve on the water pump housings, some owners have put a grease fitting in place of it and the grease has no place to go other than blow the seal and fill up the fan hub.

there are single double and tripple lip seals and sliding shaft seals that have a wiper to clean the shaft these are mainly used on rams the idea is the wiper protects the seal by removing dirt so it cant damage the seal itself.

rotating shafts normaly use single or double lip seals if you have a choice use a double lip seal. the seal should always have the tensioned portion facing to the side tha is wet unless it is used as a relief and a seal as rome stated about track rollers

I took an hour meter apart to clean it, do not use brake clean! It wipes out the numbers.