Cat D4 2T, major oil leak

750owner

Member
Hello, any D4 gurus out there?

I have a ~1945 D4 2T series, admittedly a little bit of a fixer upper but got it for a song. It seems to be a strong, well running machine and the previous owner added OROPS and a brush rake.

Except...

When I got it, I didn't realize it but it had a major oil leak. It's coming out of the flywheel case. There's a ~2" threaded hole on the transmission side (as I recall) and there's no plug or anything in it. When I say major, it leaves a continuous trail of oil behind it under some circumstances, which seem to be angle related (i.e. if on an incline up).

I needed to do some work so I kept adding lots of oil, but now I need to fix it. Originally I assumed it was the rear crankshaft bearing.

I have a full set of manuals for this machine, but I thought I read somewhere that it has a common engine/transmission oil system. I can't seem to corroborate that now though, so maybe not.

However, if there is indeed a common system, the leak could be somehow related to the flywheel clutch bearing which it needs to be regularly lubricated. That bearing/seal can apparently be replaced without pulling the engine.

Any thoughts on this? I am leaning toward the crankshaft bearing seal.

Has anyone pulled an engine on one of these? Seems pretty doable. Or can I replace the seal without completely pulling the engine out?

Any advice appreciated.

Thanks!


On a side note, has anyone ever done an electric motor/glow plug upgrade on one of these to get rid of the pony motor? Or maybe drop in some other diesel?
 
After reading this, your thoughts are all over the place. You need to read the manuals and understand how the tractor works mechanically. I believe I have a military technical manual in my collection, which is Operator Instructions, Serviceman's Reference Book, and Parts Catalog. Hopefully you have those 3 and they match the serial number range of that tractor. I'd have to refer to one of those to refresh my memory in regards to that 2" hole in the side of the transmission.

Engine and Transmission do not share oil, 2 separate components.
Flywheel clutch, pilot bearing is not in an oil bath, it's a dry clutch assembly, that has a zerk fitting to lubricate that bearing.



Pulling the engine on this one, you'll need something strong enough to hoist and you will want to take note of how it's installed, shims and such. I may be wrong but on the re-installation, alignment radially and axially to the fly wheel needs to be within tolerance. It's like this on larger caterpillar tractors of that era.

What are you doing to monitor oil level? Are you pulling a dipstick or a plug from one of the housings ? If rear main seal on the motor, then you would be pulling a dipstick from the side of the engine block. It sounds like a possibility, if the oil is coming into and through the dry clutch compartment.

This engine has pre-combustion chambers, not so sure any kind of glow plug can be added, forget that idea. Re-powering with another engine, possible, but could be a project. You would be better off with the OEM engine. You can change to direct electric start, but that requires a hole in the flywheel housing, a certain starter motor with the correct gear, + batteries, cables etc. It's likely $1000 or more.

A good running starting engine is in my opinion better than direct electric start. If you live in a cold climate, even better. Thing is most do not know these 2 cylinder engines, they get cobbed up and don't run as they should, making the starting process a pain in the neck. The starting engine benefits are that you can spin that engine for a long time without compression get oil and coolant circulating, combustion chamber warms up and the engine is lubricated well before it fires in cold temperatures. No electric start will give you that. These must have good fuel flow and hot spark to run correctly. Also be aware that fuel can contaminate the crankcase oil on some of these era tractors, always check the oil for thinning and gasoline contamination and change it regularly. Some of these you must have the engine spinning to get coolant to circulate through the starting engine. I'm going off memory, I'd have to refer to the manual to verify.

Only other compartments are the transmission, bevel gear compartment and final drives. If these are not leaking profusely, then at least you know it's the engine, but you will have to determine what is leaking before doing any repairs. Final drives and sprocket removal requires special tooling, a heavy duty puller designed for the purpose.
 
As Billy said you have to determine what is leaking oil---the engine and transmission are separate compartments so what have you been refilling? The transmission compartment also includes the bevel gear case.
These engines do not have a rear main seal--it is a bearing with a screw thread groove to return the oil back to the crankcase--sometimes the groove can just get filled in with sludge--or it may just be very worn.
 
Thanks Billy NY and dpendzic.

I stand corrected about the shared oil system--I thought I had read that somewhere but as I said, I didn't see that in the manuals. (Yes, I have all three.) Hence the reason for my confusion. Thanks for confirming.

The oil is definitely coming from the engine, as measured by the dipstick. So I am guessing the rear crankshaft bearing is leaking.

These engines do not have a rear main seal--it is a bearing with a screw thread groove to return the oil back to the crankcase--sometimes the groove can just get filled in with sludge--or it may just be very worn.

Are you saying that the bearing may be plugged and hence isn't returning the oil? That's something I wasn't aware of, thanks.

What is the least amount of work I can do to clean or replace it? i.e. is there a way to do so without pulling the engine completely?

Insofar as dropping in a different engine, I find the pony a major PIA, though the pony runs well when there isn't moisture in the points housing (ugh...). It takes a good while though for the diesel to warm up enough to start, helped along with a good amount of ether. It's a pretty bulky block, so I figure most straight 4's should fit in there. Anyway, just a thought. It's a strong dozer like I said, would be great to have it be more readily functional.

Thanks again.
 
A high quality diesel engine oil may help to clean out the sludge in that bearing's grooves over time. I don't have my engine repair manual handy to see if the rear main can be changed by just dropping the pan.
Are you warming up the diesel engine under compression, the run position on the compression release lever? You should not use too much either--Cat says 2 to 3 sec bursts
 
A high quality diesel engine oil may help to clean out the sludge in that bearing's grooves over time. I don't have my engine repair manual handy to see if the rear main can be changed by just dropping the pan.

Good to know, though I'll go broke buying that much high quality oil!

Are you warming up the diesel engine under compression, the run position on the compression release lever? You should not use too much either--Cat says 2 to 3 sec bursts

Yeah, warming it up as per starting sequence in the manuals, though I've tried variations. I'll give it a periodic ether burst into the air intake after about 5 minutes with the pony alone, and when it starts coughing, a series of short bursts (<1/2 sec) until it runs on diesel alone. After that it does take a good while to warm up thoroughly though and run smoothly. I haven't checked compression.
 
Have a D6 9U that is pony. You can motor it for hours then shift compression then throttle of diesel half way and it will not start. From a cold start, motor it for 2 minutes and shift compression then throttle of diesel to full throttle and it will start immediately. You might try throttle position in starting process from full idle (advanced further than the shut-off position) to full throttle a few times and see where the engine starts best. If you find it still hard to start, check linkages in the throttle/governor first, then make sure compression is high enough to run and the rpm of the pony while you are cranking the diesel is adequate. If you use a lot of starting fluid, the rings and cylinders may be damaged. If your D4 is that hard to start on diesel, an electric starter is definitely not the answer; MONEY WASTED!
 
Not sure what you are looking at when you talk about a 2 inch plug in the back of the engine, but could it be a drain for mud and water from the clutch compartment? See manual. These were usually left out when operation is in dry conditions; replace when fording water or extreme mud. You will likely find several more of these plugs/holes in the steering clutch and possibly other places. Engine clutch is dry type and I would guess steering clutches are dry type. I had a D4 7U with steering clutch problems and sold it because of them. Wish I had it now with my shop equipment, I would tackle the problem.
 
Hi Rustcollector,

Thanks for weighing in. I'll try that procedure next time, nut I definitely need to get the leak taken care of before I can really do anything. While I have the oil pan off, I'll take a look at the cylinders from the bottom. Maybe a new set of rings and a honing job are in order when I have it apart--easy enough. I don't want to do a full rebuild though... We'll see.

Yes, the holes are associated with the clutch compartments, one for the engine clutch and two in the back at the final drives. The oil leaks out of the engine clutch compartment, at the rate of maybe 0.5-1 cup/minute, way too much to try to operate. The odd thing is that it was intermittent when I was running the dozer. It definitely did it going uphill, but not always on the flat. I think it didn't going downhill.

Anyway, has anyone pulled a D4 engine? It doesn't seem to be too complicated, but I'm wondering about the time it takes.
 
there are drain plugs for the dry main clutch and the two steering clutches, the final drives are wet with gear oil but do have a drain plug on the bottom, as does the transmission
 

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