Oil return problem

comnoz · May 19, 2010

I copied your picture to photo-bucket and edited it there.

If that lower drainback hole actually intersects the oil return channel , it is a modification I have never seen before and definately needs to be fixed. That would undoubtably account for a wet-sumping problem with or without a filter although a filter would make it worse.

I thought that hole near the main bearing was likely the bolt modification to stop the main from turning in the case. Jim

ML · May 19, 2010

Just a thought, I understand the Atlas timing cover must not be used on the Commando case as one or the other of the oil way holes are different?
If this is true, is it possible the problem being debated has inadvertantly fitted an Atlas cover (the Norton logo on the timing cover would be slanted down when fitted).

Mick

comnoz · May 19, 2010

I don't think an Atlas cover would relate to this problem. The Atlas cover on a Commando problem arises if you use an atlas cover with the channel drilled to return oil to the inlet side of the pump and the Commando case you have does not have the channel drilled through into the inlet channel. Then the oil pressure relief oil has no where to go and breaks the pump.

Or if the cover does not seal the drilled channel in the crankcase it will allow the oil tank to drain into the engine . Jim

L.A.B. · May 19, 2010

ML said:
Just a thought, I understand the Atlas timing cover must not be used on the Commando case as one or the other of the oil way holes are different?
If this is true, is it possible the problem being debated has inadvertantly fitted an Atlas cover (the Norton logo on the timing cover would be slanted down when fitted).

But that would only affect the drillway in the gasket face. The Dominator (and presumably Atlas) OPRV vents into the timing chest, so the cover doesn't have the matching gallery at the gasket face that Commandos do because the oil from the OPRV is recirculated back to the inlet side of the oil pump.

Curiously, the 850 MkIII models reverted back to venting excess oil into the timing chest again, so the MkIII timing covers do not have the gasket face drilling, although it was still there in the MkIII crankcase.

L.A.B. · May 19, 2010

comnoz said:
The Atlas cover on a Commando problem arises if you use an atlas cover with the channel drilled to return oil to the inlet side of the pump and the Commando case you have does not have the channel drilled through into the inlet channel.

All Commando crankcases should have had the recirc. drilling, but I'm not sure any Atlas timing covers did?

comnoz · May 19, 2010

That may be right. I ran into a problem with a broken pump after swapping covers once but it was too long ago to remember which cases were involved but it was on a earlier 750 commando. Jim

Bobolink · May 20, 2010

There is no issue with the relief valve recirculation, drilling back into the pump as should be.

LAB. Your picture of "20M3S early" looks just like mine, I wonder where "that hole" goes on that set of cases.

My eng No. is 151***.

Regards

Bob.

myjota · May 20, 2010

I had exactly the same problem on my early 72 750. Turned out to be tab from camshaft thrust washer in oil pick up hole.

comnoz · May 20, 2010

myjota said:
I had exactly the same problem on my early 72 750. Turned out to be tab from camshaft thrust washer in oil pick up hole.

You were luck, usually the tab ended up in the pump. Jim

Oil return problem

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