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ET: Engine (Twin) Oil Leak

nigsey

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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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stumpy lord

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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.
If as you say, the gear box oil is contaminated the( oil should be clear ) I would consider draining the oil and refilling with a good E P oil. In all the years I have owned a vincent I have never seen the oil come out contaminated as you described , possibly the machine has been sitting for a long time and, condensation has formed in the gear box causing some corrosion to form.
Whilst doing that you could always calibrate the the dip stick.

An old simple dodge to prevent oil seeping down the main shaft is tap the bush G16 (should that be G17? BigEd ) back into the shaft G4 and fit a very fine O ring between the end of the shaft, and G26 ratchet spring cup.
 
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Bill Thomas

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VOC Member
How are you checking the gearbox level ?,
Leaning on the wall ? or the back stand ?.
Always wipe the stick every time, I got caught out years ago,
The splash can stay on the stick a long time !!.
I also use thick oil in the Gear box, 80 or 90, That also might help ?.
 

nigsey

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VOC Member
Many thanks for all your replies and suggestions. The latest news is that I drained the gearbox and refilled with Castrol EP90, hopefully that oil is acceptable in a twin. The drained oil was reddish brown in colour with minute glittering particles in it, at the bottom of the container there were a small amount of grey sludgy bits that looked more like aluminium. I fired the motor up and went for a short ride and no oil whatsoever came out from underneath. I checked the oil level in the primary case and it looked low but looking through the inspection cap the colour of the oil deposits on the sprockets appeared to be the same reddish brown, so I’m wondering if the problem does come from this side.
 

nigsey

Well Known and Active Website User
VOC Member
How are you checking the gearbox level ?,
Leaning on the wall ? or the back stand ?.
Always wipe the stick every time, I got caught out years ago,
The splash can stay on the stick a long time !!.
I also use thick oil in the Gear box, 80 or 90, That also might help ?.
Thanks Bill, the bike is up on the Hills centre stand.
 

Bill Thomas

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VOC Member
Vincents are funny old Bikes, As an old racer I like big breathers,
As Peter said pressure can go from one place to another,
But not all bikes suffer from this.
The gearbox breathes from the flats on the dipstick, Then through small holes in the filler cap,
The chaincase should breath through the gap between the dynamo or alternator and the case,
BUT some of us seal it there to stop oil leaking, Which could make pressure in there ?.
But as I said One bike may do it and another not !.
Guess which way I have gone !!.
 

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Cyborg

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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.
F19B8421-D0E9-4696-A4DC-C8CC6E1B5D53.jpeg
 

timetraveller

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VOC Member
I really do not want to be depressing about this but if the gearbox oil had bits of any colour metal in it then something is, or has, broken up. It sounds as though one or more of the Oilite bushes has collapsed, to give the red/bronze colour, and the aluminium sludge sound like something is wandering about and chewing up the casting somewhere. It is not a big job to remove the primary chain case cover, the clutch and then the access hole to the gearbox. Having a look might save you a lot of money.
 

nigsey

Well Known and Active Website User
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.
Thanks Peter, everything looks perfectly clean and shiny in the primary case, certainly no signs of rust. As I say, the oil on the gearbox dipstick looked perfectly clean on the several occasions I checked it when I got the bike and after taking a few short rides, it was only after I topped up the primary with oil, which was low and I’d run the motor did the excessive level on the dipstick appear, along with the reddish brown oil.
 

greg brillus

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If the drained gearbox oil was a red rusty colour, then either a gearbox bearing has failed and/or there has been moisture in it causing rust on the gears and shafts........In either case the gearbox would be noisy when riding that is most noticeable.........A normal Vincent twin gearbox does not make any noise.
 

Colin

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Nigsey
Dipsticks seem to come in a variety of lengths, and yours is not necessarily the right length for your bike.

As i have said before there is a reason "Dipstick" is a derogatory expression
 

nigsey

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VOC Member
Nigsey
Dipsticks seem to come in a variety of lengths, and yours is not necessarily the right length for your bike.

As i have said before there is a reason "Dipstick" is a derogatory expression
I put 1 x litre of oil in the empty gearbox (1.76 pints) and it just appeared on the bottom of the dipstick, so I guess that is about right and is what most recommend. No oil has leaked out yet, touch wood.
 

Peter Holmes

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Have you ridden it since refilling the gearbox, that is when I would expect the leak, if there is a leak, to manifest itself, not necessarily when static. When you are riding the oil get flung about a lot, seeking out opportunities to leak, also if you do have any pressure build up problems they also will not manifest whilst static. Good luck, I hope your refilling to the correct level has fixed your problem.
 

nigsey

Well Known and Active Website User
VOC Member
Have you ridden it since refilling the gearbox, that is when I would expect the leak, if there is a leak, to manifest itself, not necessarily when static. When you are riding the oil get flung about a lot, seeking out opportunities to leak, also if you do have any pressure build up problems they also will not manifest whilst static. Good luck, I hope your refilling to the correct level has fixed your problem.
Peter, many thanks for you help. Yes I have ridden the bike since changing the gearbox oil and am pleased to report that not a drop of oil leaked out, just the usual few drips from the breather pipe.
 

Bill Thomas

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Should it be 2 pints ?, You don't want it too low !.

With the breather, If it's standard, I think the pipe should go upwards,
I know that's not how the works did it, But with an old engine you are bound to get a bit out ?,
If it goes up for a bit, A small bit will run back down into the engine ?,
JUST MY THOUGHTS.
 

Hugo Myatt

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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.
“Is it possible for engine oil to migrate to the gearbox?” Under certain very specific conditions the answer is yes. This happened on my Rapide about twenty years ago. A quick but not infallible test is to temporarily fit a D type breather cap, or some other large bore breather to the primary chaincase. If, on riding the bike, the oil level in the gearbox ceases to rise but the level in the primary chaincase rises the following saga may be of interest.

The whole saga was recorded in MPHs 561 to 569 and also in “Another Ten Years.”

My Rapide engine had recently been rebuilt by a renowned and much-lamented Vincent expert. He had incorporated many subtle and successful modifications. Unfortunately, there was a “Market Garden” syndrome in that there was one modification too far, but back to that in a minute.

There had always been a slight oil leak from the dynamo drive and I went to a great deal of effort to completely seal the drive. In this I was completely successful. With the standard filler cap fitted the primary chaincase was completely leak free. This is when the trouble manifested itself.

After riding the machine, I checked the oil level in the chaincase. Horror! There wasn’t any! However, the oil in the gearbox had risen rapidly.

After a great deal of investigation, frustration and consulting all sorts of experts I eventually discovered what was happening. The final mod the re-builder had incorporated was to use a sealed bearing in place of E91, the outer drive side main bearing. This bearing had the inner seal removed leaving only the outer seal in place. He also dispensed with ET 77, the reverse oil scroll spacer and replaced it with a plain spacer. The unfortunate result of this modification was to make the half-sealed bearing an exceedingly efficient ‘’flap valve’. As the pistons descended this forced engine oil into the chaincase whilst pressurizing it at the same time. When the pistons rose the ‘flap valve’ shut off equally efficiently so trapping the added pressure in the chaincase. This meant that the pressure in the chaincase rose exponentially with every movement of the pistons and having nowhere to breathe the chaincase oil was forced to escape the only place it could – through the gearbox mainshaft oil seal into the gearbox. The gearbox oil seal is designed to prevent oil from leaking out of the gearbox and not preventing chaincase oil, under extreme pressure, entering the gearbox.

Sadly, the only cure for this was an engine strip down and a reversion to the standard arrangement for the drive side main bearings, that, and less than total sealing of the dynamo drive.
 

nigsey

Well Known and Active Website User
VOC Member
Well, I have unscrewed and eased the primary casing to drain the oil therein and it is the same reddish brown colour that came out of the gearbox, albeit this oil looks totally free of any glittery bits. Is there a possibility that this oil and the gearbox oil was originally this colour from new, excluding the glitter of course? Approximately 250ml came out of the primary, I don’t know what it should take but I had topped it up to the correct level just before oil started leaking out on the main drive chain/gearbox side when I ran it up.
 

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