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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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Bill Thomas

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VOC Member
Check to make sure the leak is from there,
I don't think it is, It's common to have those marks, Maybe not so bad as yours,
I mean there is a stud under that point.
As had been said before , It's easy to put too much oil in the gearbox,
The dipstick often reads wrong,
The best thing to do is drain the gearbox and fill with the right amount,
And see where it comes on the dipstick, Often it's at the very end tip , Not half way up the flat ?.
 

Peter Holmes

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VOC Member
Hmmm, Clearly the chain has been run slack over a period of time, it is not that uncommon to see that sort of carving away metal by a loose chain, but I very much doubt that is where your oil leak is emanating from, more likely the sprocket oil seal has seen better days or an overfilled gearbox.
 

nigsey

Well Known and Active Website User
VOC Member
Check to make sure the leak is from there,
I don't think it is, It's common to have those marks, Maybe not so bad as yours,
I mean there is a stud under that point.
As had been said before , It's easy to put too much oil in the gearbox,
The dipstick often reads wrong,
The best thing to do is drain the gearbox and fill with the right amount,
And see where it comes on the dipstick, Often it's at the very end tip , Not half way up the flat ?.
Thanks Bill, yes the oil does appear to be a little way up the dipstick, I’ll drain the gearbox as suggested and refill paying attention not to overfill. I haven’t interfered with the gearbox since I bought it, neither changed the oil or added to it, but then I appreciate the buck stops with me!
 

nigsey

Well Known and Active Website User
VOC Member
Hmmm, Clearly the chain has been run slack over a period of time, it is not that uncommon to see that sort of carving away metal by a loose chain, but I very much doubt that is where your oil leak is emanating from, more likely the sprocket oil seal has seen better days or an overfilled gearbox.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Nigel, Just a thought, If oil was coming from there,
I think the stud comes all the way through from the other side ?,
Inside the Primary chain case, When we put the studs through we put sealer under the nut
which is bashed into a hollow recess, Oil could run along that stud ?,
Don't think it's that, But keep an eye on the primary level also.
Cheers Bill.
 

nigsey

Well Known and Active Website User
VOC Member
Nigel, Just a thought, If oil was coming from there,
I think the stud comes all the way through from the other side ?,
Inside the Primary chain case, When we put the studs through we put sealer under the nut
which is bashed into a hollow recess, Oil could run along that stud ?,
Don't think it's that, But keep an eye on the primary level also.
Cheers Bill.
Bill, you just might be onto something there. I topped up the primary oil recently because it was very low when I checked it, bit of a coincidence maybe? incidentally, I made sure the oil didn’t go above the level plug.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Not sure if it's one of the studs I am thinking about, But just to show you the recess in the primary side,
There is a nut brazed onto the end of the long studs,
This is a photo from Robert USA,
I would try and seal it from the outside if you are sure where it is coming from,
But Vincents are known for oil leaks coming from far away from what we think !!.
 

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Robert Watson

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At the risk of starting an international incident That would be me.

Robert - from the west coast of Canada ---- Canada. To be fair I only live 8 miles north of the 49th Parallel but the border has been closed for several months so it doesn't even count as close!

Loke others I would say an overfilled gearbox and oil getting past the seal or in between the main and output shafts.
 

nigsey

Well Known and Active Website User
VOC Member
Not sure if it's one of the studs I am thinking about, But just to show you the recess in the primary side,
There is a nut brazed onto the end of the long studs,
This is a photo from Robert USA,
I would try and seal it from the outside if you are sure where it is coming from,
But Vincents are known for oil leaks coming from far away from what we think !!.
I’m with you now, will see how it goes. About an egg cup full of oil leaked out in quite a short time of running it up, I must admit it made me feel a bit sick (with worry).
 

nigsey

Well Known and Active Website User
VOC Member
At the risk of starting an international incident That would be me.

Robert - from the west coast of Canada ---- Canada. To be fair I only live 8 miles north of the 49th Parallel but the border has been closed for several months so it doesn't even count as close!

Loke others I would say an overfilled gearbox and oil getting past the seal or in between the main and output shafts.
I hope it’s something as simple as that Robert. I liken Vincent ownership to having a child, worrying about them all the time.
 

Michael Vane-Hunt

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VOC Member
At the risk of starting an international incident That would be me.

Robert - from the west coast of Canada ---- Canada. To be fair I only live 8 miles north of the 49th Parallel but the border has been closed for several months so it doesn't even count as close!

Loke others I would say an overfilled gearbox and oil getting past the seal or in between the main and output shafts.
Pacific South West. Please.
 

nigsey

Well Known and Active Website User
VOC Member
Checked the gear box oil level this morning and it’s very high, just beyond the top of the flat on the dipstick. Now I had checked this several times since I bought the bike and it has only ever been just showing on the bottom of the flat, the other thing is that the oil is a reddish brown colour now when it was clear before. I have neither changed the oil nor topped it up since I’ve had the bike, the only thing I’ve done is add oil (to the correct level) in the primary case which appeared virtually empty when I got it. In which case, has the oil I added to the primary found its way into the gearbox?
 

Peter Holmes

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VOC Member
Reddish brown sounds a bit like rust contamination, not totally unheard of in the primary chain case due to condensation. There is a long explanation of this phenomenon on this forum somewhere, I would search Hugo Myatt, basically the engine can pressurise the chain case through the main bearing, and the pressure in the chain case forces oil into the gearbox, I am not for one minute saying this a definitive explanation of your problem, but perhaps something you should consider, if that does prove to be the problem, I have to tell you there is no quick fix.
 
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vibrac

Well Known and Active Website User
VOC Member
Peter is probably right about the source if it was clean or black its not unknown to come direct from the engine I dont think its a cue 1960 gearbox breathers but like the twin racer with a belt dry chain case a seal behind the output sprocket is a solution
 

greg brillus

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VOC Member
If the oil leaking out is similar to the colour of the oil in the gearbox, it could likely be the output shaft bushes have collapsed, thus the red/gold tinge coloring of the oil........not an uncommon problem, and not too difficult to repair, if not messy.
 

Peter Holmes

Well Known and Active Website User
VOC Member
Gregs suggestion is a good one, I have had this happen myself, but you can normally see the small glittering particles of bronze, or whatever it is in the oil, it looks like liquid metallic paint, and would collapsed bushes lead to unexplained excess oil in the gearbox that wasn't there previously, that oil had to come from somewhere.
 

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