wet sumping

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May 15, 2009
Hi all, can anyone tell me when all the oil has gone to the sump do you need to go to the bother of returning the oil to the tank or is it safe to start bike and pick it up at tick over Brian
I think some owners do tend to do that.

If the oil in the tank has been allowed to drop to the level of gauze feed strainer (you can see it through the oil filler if it has) , then it must be assumed that air will have entered the feed pipe between the oil tank and the engine, therefore if you were to start the engine, the oil pump would be supplying mostly AIR to the big end bearings instead of oil, even though the scavenge side should start to refill the tank almost immediately on start-up, it could still take many seconds for the oil to get down the feed pipe from the tank to the pump. I'm not sure if doing that actually causes any premature big end wear or not, but I don't do it.

There's also the chance that the drive side oil seal will be blown by excess pressure due to the sump being full of oil, so you could end up with engine oil leaking into the primary case.
When I was dumb kid after a bus trip (I drove SF to NYC) I'd add a spot of oil to pump and start it and let it idle to bring the oil up. I had a huge tank so it always had room for the excess oil, my current one would overfill and blow it out on my leg.
These days I'd drain and refill and that's what I was doing until I fitted the anti drain back valve.
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