Was the function of this one-way valve to pressure regulate gear/primary compartment into crankcase?
xlfan, I am no expert so sorry for this more opinion than fact, and based solely on "lore" that I've heard over the years. The early XLs ran a dry clutch, so oil level in the primary is critical. Should somebody overfill the primary, or the left side crankshaft seal fail and it starts burping oil into the primary, the clutch will get oil soaked. So I think that valve is there to allow the engine to suck oil back into the crankcase on the piston upstrokes. The early XL trans/pri vents through a little hole in the filler plug on the side of the pri cover, not through that oil transfer valve.
-JW
Here is my spin on the transfer valve function.
I believe the transfer valves purpose is to save oil, when the motor sumps the transfer valve allows oil to migrate into the primary.
The transfer valve disappeared when the oil pump was upgraded to the non-sumpy one.
Thanks :up: