I believe the rear main seal may be bad in my D4 (SN 37436), unless there's a trick to these machines that I'm missing. It's a dry clutch and there's not diesel in the oil. The engine oil pumps into the clutch housing compartment after the machine is warm and has been running a little while (was using it on a disk). It didn't seem to do it while cold/stationary. I've already checked the engine crank case breather and it's clean. Is there anything I'm missing or is it safe to say the rear main seal is bad?

Next question, if it is the rear main seal, whats the best way to change it? Does the engine have to come out or is there a way to do it with the clutch removed?

No rear main seal, just close tolerances so the big reverse screw thread on the crankshaft brings oil back and dumps it into a channel behind the actual bearing area with a drain to the sump. Sounds like your bearing clearances are probably at max wear thus opening up the screw thread area which allows oil to leak. I think there was a kit to add a lip seal type rear main seal for tractors operating on inclines where oil transfer was a problem. I have never seen one but it has been discussed on here before.

Hi Team,
as CCJ says there is no positive oil seal at the rear of the crank--just an oil scroll.

First thing to check is the condition of the crankcase breather filter screens-- in the canister on top of the oil filler elbow.
If this clogs then any engine blow by flow can build up pressure in the crankcase and force oil out thru the scroll into the clutch compartment--keeping this screen clean is important for this reason.

As well as worn main bearings changing the designed gap around the crank and its bearing bore, the drain back drilling mentioned can clog with oil sludge if maintenance has been neglected. Other leakage path can be via a compressed packing between the rear main bearing cap and the cylinder block--usually shows soon after being put into service if the packing has not been installed correctly and tightly packed--fiber packing string similar to pump packing etc.

The machine Maintenance Instruction says to wash and oil the breather screens every 250 hours of operation or I would recommend to do this more often in dusty conditions.

Hope this helps.
Cheers,
Eddie B.

The crank case filter is clean and not filled with dirt. The dozer has been sitting for a while before I got it, so it has not been apart in quite some time (if ever). I am thinking the drain passage could be blocked from the responses so far or maybe the packing has worn down? Can anyone tell me if the drain in the main bearing back to the sump is accessible with the engine in place by removing the oil pan?

Thanks

I know this may be a long shot but can someone show me where this, what I have in () located.
Please and thanks. Ive been working on this d4 with my husbandand im confusedon where this screw is locate. (bearing clearances are probably at max wear thus opening up the screw thread area which allows oil to leak. I think there was a kit to add a lip seal type rear main seal for tractors operating on inclines where oil transfer was a problem)

it not really a thread it just a helix machined onto the end of the crank. yes if the main bearings are worn out and it has worn the castings where the crank exists the block it will leak.

it might be possible to get to by removing the sump. im not sure never had to go that far with ours. but you would have to remove the engine to fix it anyway. and if crank bearings are gone then everything else in the engine needs attention anyway.

get yourself copies of the parts,service reference and owners book for your machine the parts book is handy to understand where things are in relation to other parts.

      You can see from the pics when the rear bearing main cap is installed there is a rope seal that goes down both sides.  The crank uses the scroll to pull the oil back into the pan.