I have a 1969 BSA B25 Starfire that is leaving a larger than normal oil pool underneath. I've checked in my handy, dandy Workshop Manual and it suggests a stuck scavenge non-return valve. The method recommended is to use a piece of wire to push the ball inside up and see if it falls of it's own accord. I'm thinking it doesn't, so the manual recommends immersing the pipe in petrol for a short period.
That's all well and good. But how do you do that? The valve appears to be a small pipe sticking down about 6-10mm and seems firmly affixed to the crankcase. How the heck do you immerse that?!
Thanks.
The scavenge non-return valve simply stops the oil in the section of pipe between the oil pump and the top of the oil tank from flowing backwards into the sump - at most, this involves 0.25L of oil and probably a lot less. If the valve stops working, the worse that will happen is that this amount of oil will well in the bottom of the engine until the next time it is started. It should not cause any problems whatsoever! Note: it is the feed non-return valve that prevents wet sumping which is when most of the content of the oil tank finds its way into the bottom of the engine.
If you have a bad oil leak from the bottom of the engine, it may be due to the sump plate not sealing properly, in which case, you will need to remove it and check the sealing. Check the plate is flat and then renew the gasket and, if necessary, use a bit sealant as well. If the oil is not leaking from the sump plate then check it's not leaking from the gear box or timing covers.