Plunger Primary Chaincase Leak & Level?

[LJ.]

I had the primary chaincase cover off the 49 Star Twin this morning as it was leaking badly. Cleaned it all out and dried off the oil inside the case ready for a nice application of gasket seal, actually I was suprised the case has only recently started leaking and seemed to be getting worse. The bike has been standing for nearly ten weeks or so while I await patiently for the tank to come back from the chromers! 

I was wondering how come there is no oil level scew and also wondered how much oil should be in the case? perhaps it does not matter as the clutch is enclosed in the top hat cover keeping it oil free so perhaps 'more oil the better in there??' 

Anyhow, I found out why it was leaking, it seems that with the bike standing for so long, the bike has wet sumped and oil is passing through from the sump to chaincase, take a look at the first picture and advise me if a leak here is 'Okay' This is a problem where bikes need to be run often, to avoid wet sumps and filling of chaincases! I suppose the case will only fill to the level thats in the sump, which is why I wondered if an overfill would be okay because I doubt if the oil would flow back into the sump when bike is restarted. 

I also found out where the oil was leaking out of the chaincase to the outside world and it appears to be leaking from one of the forward bolts, now looking at the second picture you will notice a 'notch' around the bolt hole, the other holes do not have this notch. The question... why is it there? its not a chainworn notch and looks as if its purposely machined by BSA for some reason. So I have somehow to make this hole oil leak free. Can anyone advise on this notch??

[A10Boy]

LJ

Unless I am getting my models mixed up, the notch is there so the screw acts as a level plug. Fill it to that level and let all the surplus drain out before replacing the screw. Dont over fill as plunger clutches don't like to be contaminated, that's why there is a cover over the clutch.

Also, it looks like your crank oil seal has failed, but you should be able to replace it from the outside once you've taken off the sprocket and cush.

Blimey 10 weeks, that's some going !!

[trevinoz]

A10Boy, there was no crank seal fitted until 1953.
Trev.

[LJ.]

the notch is there so the screw acts as a level plug. Fill it to that level and let all the surplus drain out

Thanks Andy!

I gave it some thought this afternoon after posting the first message on this and it does indeed look just like what you've said.

I also managed to rig up a very tempory fuel tank, bit like a hospital drip bag, and fired the bike up just to clear the sump. Hopefully the sump should stay clear until the proper tank gets back and I can run the bike much more regularly.

Thanks Trev concerning the crank seal or lack of, guess I'll just have to run the engine regularly and occasionally check the chaincase level.

[LJ.]

It's amazing isn't it? Such a simple thing that can easily be missed. I would simply have not known if I had not asked what that notch was for and of course its all so obvious when told, you learn something every day and this is the satisfaction I get from owning old bikes and using this forum. Makes me wonder though how many bikes that have wet sumped and oil had flowed through bearings and worn or missing oil seals and filled up chaincases and then later owners wonder why their clutch is slipping!

So there we have it in the picture below, sealed up chaincase cover, filled up to extent of overflow, then when stops... In goes screw with 'O' ring. Job done! 

[A10Boy]

Another happy customer !! 

Not being too familiar with your model, does it have a sump plate like later pre units? If so, you could fit one of those finned alloy sump plates with a magnetic plug, then just drain any oil from the cases as and when needed.

Trev of course you are correct, I kinda had that feeling going on as I was writing!