I've had the engine oil in the bike for around 2 months now, with no major leaks. I've run the bike a few times with no noticeable leak, other than a bit coming from the breather due to wet sumping.

2 weeks ago I filled the gearbox, turned it a few times, and topped up till it was running out the filler. This morning I discovered a large oil slick under the bike. The oil tank was almost empty and the gearbox drive 'looks' like it has a drip underneath. Have I overfilled? The way the bike is sitting on the jig I've made it's tricky to tell where it's coming from. Any ideas? I'm using 20/50w oil for both.

Thanks.

email (option): Adh325@hotmail.com

Andy, I once found the gearbox case screws had worked thier way loose so it dumped the oil.

Andy, I once found the gearbox case screws had worked thier way loose so it dumped the oil.

Did you happen to park a Norton near it in the past 24 hours? That does it to my BSAs Every Time!

email (option): chri@classicbikebooks.com

Checked all the bolts etc, all seem ok.

The plot thickens though, on a whim I checked the chaincase - it's full of oil, and I certainly didn't fill it. The oil tank was almost empty, is it possible it has wet sumped so much that the oil has transferred from the crankcase to the chaincase - or is it more likely to have come from the gearbox?

email (option): Adh325@hotmail.com

its possible that if your crank case has filled up with oil it could leak through the drive side bearing into your primary chain case as is hasnt got a oil seal on it just a large washer which seals it to some extent when i saw the heading i thought you were going to say you didnt have any oil leaks now that would have been a big problem

Haha! I read somewhere that they were designed to leak - indication that oil levels are fine!

So if nearly 5 pints of oil has landed up in the crankcase, then leaked through the main bearing, I'm assuming that would be enough to reach the plate on the inner chaincase, which presumably doesn't have a seal either, hence my oil slick.

One the engine has wet sumped, will there always be too much oil in the crankcase until some is drained? Because presumably the oil pump will continue to draw as much oil from the tank as it is returning from the crankcase?

I've drained everything off tonight, and refilled the gearbox, just to make sure that's holding. Process of elimination!

email (option): Adh325@hotmail.com

Andy, the return side of the oil pump is more efficient than the supply side so running the engine will clear the crankcase but starting may be difficult. removing the drain plug is usually easier.

Yes as Matty said. The oil will return to normal eventually. But you will have the best smoke screen you have ever seen. Best to drain it.
Also you could renew the little ball and spring in the plug at the bottom of timing case. You can buy them from Drags or C&D for pennies. Give the ball a slight tap with a slim drift to create a good seat in the ally case. Ron

email (option): ronpier@talk21.com

I believe that ball is nothing more than a 1/4 inch ball just like in the steering head. I've used the spring from a ball point pen too. Worked great!

email (option): britool51@hotmail.com

it might not be a problem but a mm size ball is slightly smaller than 1/4" one could this cause a problem

Andy, exactly the same thing happened recently to my WM20. Unfortunately, I had to strip the clutch too. It was thick with oil. The WM20 clutch is "protected" by a drum, but the drum is designed only to deal with splash, not a flood. There's a good chance your clutch will slip when you try to start it up. Easy enough to sort out, but time consuming. I suspect you had a small bit of grit or whatnot under that little 1/4 ball in the timing case. A weak spring or worn ball shouldn't have passed that much oil so quickly. There's some muck there somewhere.

Sort that out and it should deal with the source of the problem. Watch your face if and when you remove the clutch spring.

email (option): dannydefazio@sumpmagazine.com

Ok, so 2 days ago I drained all the oil from the bike - chaincase, engine, gearbox and oil tank. I filled the gearbox again to the level of the filler, checked again this morning - another puddle. It's not leaking from the removable cover on the side of the gearbox so it must be coming from the output drive??

I remember reading that this drive doesn't have a seal - so should the level of this shaft be above the level of oil?

Maybe the grade of oil im using is too thin? (20/50 mineral)

email (option): Adh325@hotmail.com

the seal if you could look at the output shaft of the gearbox you would see some of the balls of the bearing which should almost covered with a large washer this is a so called oil seal i assume your bike is sitting straight on the ground i found if it is on the field stand oil leaks out of the bearing but not a great ammount like you say you are having i wedge a bit of wood under the rear stand to tilt it over to the kick starter side to stop this happening maybe the washer is missing

Thanks Roger, I havent actually had the main section of the gearbox apart, and there was no apparent leakage when I started the refurb. That's not to say the washer isn't missing like you suggest though.

Do you think perhaps using a slightly thicker oil would help?

email (option): Adh325@hotmail.com