ET: Engine (Twin) Oil Leak

Bill Thomas

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On the ex L/ning I have a small ball valve breather, I thought I would try it,
Maybe OK for a standard bike but mine still has big old specialloid pistons with big clearance,
So will give my crankcase a lot of pressure, So I think I am better with a BIG open pipe,
like I have always used.
 

Cyborg

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Many thanks for sending the photo, it’s a neat job you’ve made of that and certainly something I will consider doing. Took the bike out this morning and fortunately no repeat (so far) of the oil leaking out.
Just for the record, it’s not my workmanship. Just pulled it out of the bin under the bench. Not sure if it’s just coincidence, but a few Vincents shipped to the backwoods of Canada leaked so badly they could have been contracted out for oiling gravel roads back in the day.... so not surprising to see it in the bin.
Personally (now that matching numbers are all the rage), I wouldn’t modify that cover, especially if it matches the engine. Easier to modify an inspection cap, like in the photo of the bike I posted earlier. Replacement inspection caps are plentiful and can be purchased new, so no harm done.
 

oexing

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Why not better deal with the real root of the problem of pressurized primary case ?? Don´t tell me its just the air in there getting warm and exiting behind the dynamo hole. No, your engine breathing set is poor, either the timed breather is questionable or a one way valve is too sticky or a massive design so not optimal for its job. My guess you got the scroll and "tight" fitting bush device on the mainshaft, so engine air is entering the primary with consequences. You really want a decent one way valve for the engine, not necessarily an elephant trunk but something more pleasing elsewhere - valve spring cap , so you get a net low pressure engine ? This will cure your filling primary and oil leaks from there.

Vic
 

Peter Holmes

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I agree, drilling a hole in the dynamo inspection cover would be sacrilege, but surely the easiest solution, certainly just for experimental purposes is simply to fit a Series D breather cap, no modification to anything required, and easy to revert back to standard if required, you could even swap it around just to win a concours event if you wanted to.
 

Trickymicky

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My Shadow when i bought it had an unobtrusive primary chaincase breather. The top rear sprocket cover bolt was extra long and protruded out the back, near the dynamo clamp and had a a pipe connected to it. The bolt had been drilled down part of its length and a small hole drilled from inside the casing, lining up with a hole in the side of the bolt, allowing a passage for it to breathe out to atmosphere. It worked, but care would need to be taken to not overtighten it, and to make sure it was tightened to the correct place. And the volume it could handle would have limitations !
 

timetraveller

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I seem to remember that Vic (oxeing) came up with a very discrete method of preventing primary chain case pressure build up without it being visible. The idea, as I recall, was to drill a hole from inside the chain case upwards, forwards and at an angle so that it emerge into the tube through which the gearbox is filled. The chain case could then breathe through the holes in the cap for the gearbox filler.
 

BigEd

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I agree, drilling a hole in the dynamo inspection cover would be sacrilege, but surely the easiest solution, certainly just for experimental purposes is simply to fit a Series D breather cap, no modification to anything required, and easy to revert back to standard if required, you could even swap it around just to win a concours event if you wanted to.
A "D" breather cap is easy to try as the front exhaust valve cap can be removed without even taking off the petrol tank. If you don't have a "D" cap, someone might be able to let you have one on a short-term loan. Ideally, you should modify the cylinder head around the valve spring area to create a larger passage through to the valve cap. I think this may have been done on the "D"s as standard. I did this on my series "B" front cylinder when I had it off for some maintenance.
 

Bill Thomas

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I think we are forgetting, Nigel does not have a problem now !,
I think the gearbox had too much oil in it.
 

Peter Holmes

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I was more thinking of using the D breather cap on the primary chaincase rather then drilling a hole in the dynamo drive cover.
 

nigsey

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I think we are forgetting, Nigel does not have a problem now !,
I think the gearbox had too much oil in it.
So far so good after a short ish ride, when the weather improves I’ll try it on a longer run. I really appreciate everyone’s input and advice regarding my problem, I’ve picked up some really helpful advice.
 
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