Have read the American Iron series on sumping. At least the first 3 parts. Written by Donnie Peterson, who has often proven to be wrong. But he brought up something I had not heard before. In the beginning it was reported by various sources that the M8 vented into the transmission. That was proven to be wrong. But Peterson claims that the M8 vents through the cylinder heads as usual but also partially into a cavity in the transmission. First I have heard of this and curious if there is any truth in it.

 

there's a lot of 'venting' going on alright about these engines and transmissions!

 

It doesn't "vent", but does move air between them. The engine case and oil bag share air space through a passage running through the trans case. Been that way for a long time, Twin cams were the same way.

 

Thanks. Was not aware of that. I have had no reason to dig that deep into it.

 

Have to check on the M8

 

The "oil bag" is bolted to the bottom of the transmission, but there is no passage into the transmission case cavity itself between either the oil reservoir or the engine case. The transmission does connect to the primary via the transmission main shaft tunnel that the clutch pushrod runs through. As long as the main seal in the engine is doing what it is suppose to do there should be no connection between the engine and the primary.

 

Not certain why you quoted me unless you were just adding on.

To clarify, the engine case is connected to the oil bag via an air port. This air port happens to run though the transmission case but it does not enter the actual transmission.
Like you said, the actual transmission cavity nor the primary cavity are connected via any air port to the engine case.

 

Not 100% on this "Sumping " Issue, but from what Ive read the engine oil is ending up in the Transmission, is that correct? I would think it is a design flaw or poor sealing between the two "compartments" if this is indeed the case

 

Transmission fluid is ending up in the primary on the bikes with the migration issue. Bikes that are sumping the engine oil is not being scavenged from the bottom of the crankcase. There have been issues with engine oil ending up in the primary but that's rare and totaly un-related. That issue is caused by a bad mainseal on the crankshaft.

 

I just don't usually call the oil tanks mounted below the transmissions oil bags, that term I have used for the tanks mounted under the seat. Nothing wrong with it, just not the terminology I usually use.

Exactly!