Oil leak!

[SteveW]

My "C" Rapide has clean oil leaking from the underside of the fwd cylinder's exhaust nut's threads. I've isolated it to this by tie wrapping terry cloth strips around every conceivable source (ie: breather banjo, rocker oil feeds, etc) and there is only oil on the strip that is around the suspect exhaust nut's threads.
To the point, any ideas where this is coming from? I am not fogging the neighborhood with blue smoke or any smoke for that matter. Could it be a worn valve guide? I removed a metering wire from the rocker feed a few months back, not sure how that could be the culprit. Any advise would be appreciated. Thanks

 

[Albervin]

I cannot imagine how clean oil could be escaping from an exhaust. I appeared to have oil at one stage leaking around my front exhaust but it was a failed washer on the rocker feed banjo bolt. I thought metering wires were discarded by owners years ago due to improvements in materials and clearances?
Thoroughly clean the area with acetone, ether etc. Get right in deep between fins. Start the bike and let it idle on the stand for 5 minutes, paying close attention to the front of the head. Some people have been known to "dust" the area with talcum powder but don't use the Chanel or Christian Dior.

 

[Howard]

Not sure how far you've gone with your "mummifying" - the front exhaust nut is one of the lowest points on the front head, so oil leaking from the inlet feeds etc can find its way down there.
Cunning things, oil leaks - Ninjas of the problem world, hit you where and when you least expect.

Good Luck.

H

 

[clevtrev]

It`s coming past the piston.

 

[SteveW]

Thanks for the replies, I've been very thorough about tracing this leak and it does seem to be coming from the exhaust nut threads. It then drips down on to the mag cover and causes all sorts of trouble. I will try the talc idea, btw, it only leaks on a good hard run. If it is coming past the pistons Clev, I would think it'd be blowing blue smoke out my exhaust, not dripping nice clean oil on the mag. cover. I inspected exhaust outlet with the exhaust pipe off and it does not show any oil there.

 

[Hugo Myatt]

Believe it or not oil escaping from a loose or badly sealing inlet valve cap can drop down onto the fins, dribble forwards and eventually makes it presence felt by dipping off the exhaust pipe nut. This is a pain because it is difficult to tighten the inlet valve cap with the UFM in situ.

 

[clevtrev]

Thanks for the replies, I've been very thorough about tracing this leak and it does seem to be coming from the exhaust nut threads. It then drips down on to the mag cover and causes all sorts of trouble. I will try the talc idea, btw, it only leaks on a good hard run. If it is coming past the pistons Clev, I would think it'd be blowing blue smoke out my exhaust, not dripping nice clean oil on the mag. cover. I inspected exhaust outlet with the exhaust pipe off and it does not show any oil there.

You might like to think that, but as you are so sure you`ve been thorough, where else can it come from?
Being as you say, it`s clean oil, that tells me you do not have many miles on the machine, because it doesn`t take long for Vincent oil to get a colour. Maybe you`ve a drip straight from the tank onto the nut. Funnier things have happened.

 

[davidd]

Steve

It seems to me that you are confirming Trevor's diagnosis by insisting it is coming out of the exhaust port. I have found that many times the oil does not burn but comes out in a mist of unburned oil. A leak down test would tell you in a few minutes.

David

 

[SteveW]

I found some excellent leads in the VOC's Wikipedia section under "Oil Leaks". One possibility is a cracked thread where the inspection cap threads into the head (MPH 456) and also a cracked weld between the banjo and the oil feed pipe (MPH 649). Both describe my exact symptoms. Maybe, opening up only when hot? I thought I eliminated these two areas, but I may be "hopefully" mistaken. Thanks for the Replies, I'll post something when I find this bugger.

 

[Monkeypants]

My Rapide had an oil leak in that area recently. It turned out to be a crack in the valve cap itself. The crack was difficult to see as it was caused by too much force on the cap wrench. All of the flats on the cap had short vertical lines from the use of the wrench over the years and one of those lines had oil weeping from it. I replaced the cap with a spare I had been given, knowing that the problem was solved. It was a bit of a shock to still see oil leaking in the area, but now a reduced amount. It turned out that the replacement cap had a tiny pinhole in it!
Here is something else I learned- if you do have a cracked or pinholed cap, do not attempt to weld it. Instead, use JB weld or some other epoxy.
The caps are not a weldable alloy, at least the cracked one I destroyed while attempting to weld was not.
In doing so I broke the number one rule of motorcycle repair- Do not break the part you are attempting to repair!
Glen