Hi all,

My BSA M20 had been running fine until last week, when suddenly – right after starting – a large puddle of oil appeared underneath the bike. I began investigating the source of the leak and noticed a significant amount of oil collecting at the back of the primary chaincase.

At first, I suspected the breather pipe was dumping too much oil. I drained the oil tank and realized that about a liter of oil was missing. That’s when I discovered that the oil had ended up inside the primary chaincase — it was almost full.

So now I’m trying to find the root cause of this issue. Has anyone experienced this before or have any idea what might be causing the engine oil to end up in the primary chaincase?

Any advice would be much appreciated!

Thanks in advance.

email (option): info@erfgoed40-45.nl

Check that the pickup non return ball at the bottom of the oil pump is free to move and that the short tube is not blocked.

Mark

email (option): pes.sales@btconnect.com

Wet sumping (Where the oil drains through the pump into the crankcase) Is a constant problem with some of our old bikes including the M20. Especially when the bike is laid up for weeks/months. The oil will flow through the open drive side main bearings into the primary case..... Drain the crankcase and primary case into a clean receptacle and return it to the tank, before restarting the engine. Ron

email (option): ronpier@talk21.com

Thank you both. I will check this. Wet sumping could be but the motor was used a week before.

email (option): Info@erfgoed40-45.nl