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ET: Engine (Twin) Oil Leak

nigsey

Well Known and Active Website User
VOC Member
I appear to have an oil leak in the crankcase of my C twin which I think may have been caused by the main drive chain rubbing on the casing probably due to a slack chain. If that if the case I’m gutted because I’ve only had the bike a short while. Anyone else had experience of this and the problems associated with repairing it please?
 

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nigsey

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VOC Member
Nigel, When you pulled the primary case away a nats, To drain the oil,
Did you first loosen the Primary chain ?,
Because the tension blade pivot is slotted half in the outer case and half in the Crank case,
You may have had enough to get the oil out, But just check the chain tension,
You don't want the chain too tight, It can upset the clutch.
Cheers bill.
Many thanks Bill, yet another thing I was unaware of, I’m on such a steep learning curve but loving it, everyone on the forum very helpful and patient! Yes, enough of a gap to drain the oil, the case went back ok including the original gasket and so far no leaks from the joint. Checked the chain tension before running it and it was fine.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Well done, If you ever take the clutch and primary case off, It's best to loosen the chain first.
As when you put it back on the you have to locate the rear tensioner pivot in the outer cover,
easy enough as long as you know about it.
Good Luck, Bill.
 

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nigsey

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VOC Member
Not exactly subtle, mine is JUST visible exiting under the footrest mount in the first picture and the black plastic pipe going down the back of the rear footrest plate in the 2nd.

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Well I’d say that’s quite subtle actually. Great how owners come up with their own designs and solutions. I’m hoping to get away without a breather but we’ll see. My bike was restored in 2009 but not by me, it’s covered 11k miles presumably without a chaincase breather. Perhaps it was something I did that caused the leak but time will tell.
 

Bill Thomas

Well Known and Active Website User
VOC Member
As I said , The standard bike Primary case, Breathes through the gap behind the dynamo,
Sometimes too much ! , leaking oil out,
But My Twin Special which has done more miles and had a very hard life is fine as standard,
Don't know why !.
It's when we seal them up other things can happen ?.

Sorry, Looks like I am Drunk :D
 

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greg brillus

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VOC Member
On my big capacity single racer I ran an automotive type PCV valve in the breather line (a 1/2" bore pipe coming from the generator hole) up and to the catch tank at the back of the bike........after a race session the oil had been pumping out of the rear pushrod tube lower seals ( "O" rings) to my utter surprise......Such was the pressure build up in the crank case from that PVC valve...... Since put a good shield around the breather outlet and running a reed type valve instead.........So if you blank off something, then you might just spring a leak somewhere else.........I've found if the primary oil level is kept within limits, it does not loose any oil out the genny hole........If the primary is filling up, then perhaps you need to check the engine breather and revise it if necessary.
 

Chris Launders

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VOC Member
Well I’d say that’s quite subtle actually. Great how owners come up with their own designs and solutions. I’m hoping to get away without a breather but we’ll see. My bike was restored in 2009 but not by me, it’s covered 11k miles presumably without a chaincase breather. Perhaps it was something I did that caused the leak but time will tell.
Nigsey, When I said not exactly subtle I was referring to the picture Cyborg posted earlier with the sprocket cover with a fitting in the middle sticking straight out.
 

Bill Thomas

Well Known and Active Website User
VOC Member
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

Well Known and Active Website User
VOC Member
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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VOC Member
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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VOC Member
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

Active Website User
VOC Member
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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VOC Member
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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VOC Member
VOC Forum Moderator
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.
 

nigsey

Well Known and Active Website User
VOC Member
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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