Odd oiling problem...

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Bob Z.

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I am experiencing a frustrating oiling problem on my (201856) 750 engine with the rear breather and only drain plug in the bottom crankcase. Just noticed this on the last few short rides.

I noticed on start-up that the rocker feed line took a long time to fill during warm-up. I opened the crankcase sump and got a quart plus draining out and still coming. Not possible to wet sump this much right after running.

So I opened the timing case, removed and inspected the oil pump gears for damage, inspected the relief valve for movement, and didn't find any issues. I put it back together.

Started it up, and looked inside the oil tank fill hole and saw that the oil was returning from the breather tube instead of the return line. Very little coming up through the return pipe holes.

Engine runs OK, good compression. But something has happened to the oiling system.

I'm thinking there is an odd obstruction in the oil return line somewhere between the supply/return pipe connection near the OPRV and the oil tank. I'll drain the oil tank and pull the lines when everything cools down.

Any suggestions?
 
Did you do the scavenge pump pickup modification that is necessary on that style case? Jim
 
I had a similar problem. My crank case kept filling with oil after only a few miles. I discovered that the return line was kinked. I had installed all new lines earlier. Apparently one was to long causing it to kink.
 
Comnoz, the crankcase is stock. I understand through this forum the original breather design issue of getting the oil out of the crankcases and back into the tank an orderly fashion, but I thought that was under high revs/speed.

This is happening under idle conditions.

I would be happy to get the engine to you for the modification if you think it required for an old (60 yo) man and his pedestrian riding style.

As a follow up: I was in the (hot and humid) garage this afternoon and removed the oil lines and tank. No obstructions found. There was the expected thick sludge in the bottom of the tank and I'll get that out tomorrow.
Every few decades eh?

But I didn't see any thing that would keep the oil from returning through the return line.
I'll double check the suggestion of a kinked hose.
 
Bob Z. said:
Comnoz, the crankcase is stock. I understand through this forum the original breather design issue of getting the oil out of the crankcases and back into the tank an orderly fashion, but I thought that was under high revs/speed.

This is happening under idle conditions.

I would be happy to get the engine to you for the modification if you think it required for an old (60 yo) man and his pedestrian riding style.

As a follow up: I was in the (hot and humid) garage this afternoon and removed the oil lines and tank. No obstructions found. There was the expected thick sludge in the bottom of the tank and I'll get that out tomorrow.
Every few decades eh?

But I didn't see any thing that would keep the oil from returning through the return line.
I'll double check the suggestion of a kinked hose.
Click to expand...

The original forward location of the scavenge pickup caused problems at rpms over about 3500. The crank windage will push the oil to the rear of the case and then the only return will be through the vent. A lot of engines ran that way for a long time but stopping oil leaks will be about impossible.

The second problem with the forward pickup is the long, small diameter passage to the front which often is plugged up with debris, sludge and broken cam washer tabs. Once it is plugged about the only way to clear it is to remove the access plugs and run a rod through it.
I would plug it permanently and create a new port near the rear of the case. Jim
 
Thanks so much for that info.
Do you have a reference photo of the original pick-up point so I may see where/if is clogged?

I did clean out the tank with a solvent wash then soap rinse and checked the residues. Nothing stuck to a magnet.
That's a good sign, but not a cure.
 
Bob Z. said:
Thanks so much for that info.
Do you have a reference photo of the original pick-up point so I may see where/if is clogged?

I did clean out the tank with a solvent wash then soap rinse and checked the residues. Nothing stuck to a magnet.
That's a good sign, but not a cure.
Click to expand...
The first, and easiest, place to look is behind the oil pump..If you still have the timing cover off, remove the pump and check the passages behind it.

Also, there are various grub screws (little pipe plugs, removed with a flat screwdriver) that can be removed and inspected. There may also be one near the front and down on the case near the oil pickup.

To do that modification, you will need to splitt the cases. Old Britts has some info about this and a deeper explanation from Fred.

http://www.oldbritts.com/n_c_case.html
 
Try this photo.
Is this the (blue arrow) pick-up passage?

I can see how this area could get clogged with sludge and block the pick-up hole.

Odd oiling problem...
 
Bob Z. said:
Try this photo.
Is this the (blue arrow) pick-up passage?

I can see how this area could get clogged with sludge and block the pick-up hole.

Odd oiling problem...
Click to expand...

Yes, That is the passage that is prone to plugging. All you need to do [after you split the cases] is plug the existing hole and make a new port into the passage at the rear. It can be done with a mill as Old Britts describes or just use a die grinder and break into the passage at the case parting line.
You can mill the baffle away if you want but I have not found it to make any difference whether the baffle is there or not. Jim
 
Thank you. I read the OB tech article and I see where he plugs the original hole with epoxy, but does not mention locating a new hole.

On my engine still in the running frame, I think I will try and remove that grub screw that closes the oil pickup point drillway, and see what dribbles out. With a crankcase full of oil and the grub screw removed, if nothing comes out that should positively identify a plugged passage?

Then I'll work on 'the big disassembly' required to split the cases.
 
The mod shows removing the DS baffle lip but its not necessary as it stops short of the TS case and sump passage can be opened in TS floor with just a drill. I of course JBW'd my 1st Combat but left the 2nd one as is to stay oil tight unless running WOT on 2S cam over the ton, then normal mist-weeps here and there. Pieces the get in the long narrow passage while heated get extra trapped on cooling contracture.
 
Bob Z. said:
I read the OB tech article and I see where he plugs the original hole with epoxy, but does not mention locating a new hole.
Click to expand...

If the case is machined as shown in the OB article, then it uncovers the rear hole which would otherwise be blanked off by the original casting.

another-rescue-t16972.html#p210183
 
Bob Z. said:
Thank you. I read the OB tech article and I see where he plugs the original hole with epoxy, but does not mention locating a new hole.

On my engine still in the running frame, I think I will try and remove that grub screw that closes the oil pickup point drillway, and see what dribbles out. With a crankcase full of oil and the grub screw removed, if nothing comes out that should positively identify a plugged passage?

Then I'll work on 'the big disassembly' required to split the cases.
Click to expand...

Bob,
In the Old Britts mod when he mills away the baffle he removes enough material to uncover the passage at the case parting line. Jim
 
BobZ,
These crankcase mods are all well and good and I have done them all on mine, but I think your issue is something else and going through all your oil lines is what you need to d

Start ant the manifold above the PRV and work you way through the system validating both the condition of the line and their routing. Study the diagrams. It is all to easy to get these crossed up.
 
if anything is plugged outside the engine than it will blow off oil lines between the engine and oil tank. yes the scavenge side can make that much pressure. IMHO the trouble is internal to the engine

pete.v said:
I think your issue is something else and going through all your oil lines is what you need to d

Start ant the manifold above the PRV and work you way through the system validating both the condition of the line and their routing. Study the diagrams. It is all to easy to get these crossed up.
Click to expand...
 
My point is ya don't need to remove any of the DS case material just some over the TS sump passage near the seam. Its pretty shallow.
 
bill said:
if anything is plugged outside the engine than it will blow off oil lines between the engine and oil tank. yes the scavenge side can make that much pressure. IMHO the trouble is internal to the engine

pete.v said:
I think your issue is something else and going through all your oil lines is what you need to do.

Start at the manifold above the PRV and work you way through the system validating both the condition of the line and their routing. Study the diagrams. It is all to easy to get these crossed up.
Click to expand...
Click to expand...

I will not disagree with this simply because I/we/you just don't know yet. I do know it's easier and maybe advisable to eliminate external possibilities before you start ripping everything apart.

The point is, is that you have a specific problem. To jump right into a drastic solution and you may do all this work unnecessarily and perhap even still have the issue when all said and done.

BobZ, if you feel you want to rebuild from the inside, I sure won't stop you. However, I would still want to identify my original problem.
 
At least the Combats with the low down dastardly breather can pump way more oil back to tank faster than the wimpy oil pump so mainly a mess to clear off if hi rpm wet sumping but not hydro lock or other damage. Still not a bad idea to shrot cut Old Brits method by drill-grind small valley out the TS seam area to expose enough drain opening while the JBW sets up in the the front hole = done. If ya could make a series of rather tiny TS holes yo'd have an oil pump protective screen. Of course blow out the drillings before closing up cases but its just a short straight shot to pump to clear or just let the pump process it through hardly noticing that size alloy crap. My Combat pumps both worked fine after ingesting the cam washer lock tabs and also pieces from various blow ups not pressing any power or rpm at all. Oil gears were chipped-scoed in pre-Peels sump side buth still left more exit than entry flow.
 
OF course you could have a bad scavenge side in your oil pump. I suggested this to a guy once (with combat) and he sent me his pump to test on my oil pump test rig. Sure enough, it was seriously compromised. It would not keep the test rig engine scavenged. He bought a new pump and all was well again. Combat cases (72-73) suffer with this more, since there is no crankcase filter and the pump has to eat all the trash the engine makes.
 
A bit of an update:
Today I was able to remove the exterior grub screw located forward of the pick-up hole.
Crankcase oil dribbled out and when I poked a thin wire in about 6", oil drained a bit faster though I didn't see any larger bits of debris that could have blocked the drain hole.

I checked all the oil lines from the rear of the crankcase to the oil tank and found them clear.
With the tank removed I flushed the sludge from the inside and a magnet didn't pick up anything.

I would have put every thing back together but apparently the oil tank cleaning revealed some small PIN HOLES
right on the bottom of the tank. They look formed from internal corrosion. The tank did not leak prior to the cleaning.

I guess brass brazing is the correct repair for pinholes in steel?

Thanks to everyone for their comments.
 
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