Advice on "chasing oil leaks" - here's a thread that should run and run.....


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Afternoon all,

Advice time again please. This time on oil leaks!! It looks like I'm joining that well known band that fix one only to have another crop up.

C Rapide

Engine has done 2500 running in miles and I've torqued down the heads, adjusted the valve timing, found the two valve covers on the very top of the engine finger loose (under the UFM) and tightened them. I guess all of this serves to improve the sealing of the engine and therefore the pressure within it.

The timed breather is working fine, I have lengthened it to exit by the rear wheel spindle.

It appears to now have developed an oil leak which is certainly on the lower part of the engine (the cylinder heads, barrels front and back are all bright, shiny and clean now I have tightened the valve covers) and I think it is towards the rear as the back of the engine adjacent the pivot bearing spindle is splashed heavily with oil and she drips onto the floor particularly from the back.

I have read in MPH that the aerodynamics can cause a rear oil leak to be pulled forward under the engine and drop from the front - this is predominantly covering the rear of the bike and dropping from lowest point under the crankcases.

The engine has been fitted with a Grosset Electric Start with the accompanying new G50 plate.

On checking the oil level in the gearbox (I put EP 80/90 in), the level appears fine and the oil is still clean and looking like original. The oil dripping out is black and I suppose therefore it is used engine oil at a guess and not gearbox oil - again I have read of the gearboxes leaking at the back.

The bike is fitted with the original chain oiler and I will now take that off and fit a blanking plug just to eliminate possibilities - but I think I am getting too much oil for it to be just that. The feed in the tank neck is shut right down although I know they may still allow some to pass through wear.

I've checked the basics, primary drive level checked and correct, clutch housing bone dry, not a sign of any oil there. Oil filter housing checked and tight, no leak there. It is blowing a bit out of the valve lifter entrance to the timing case, but I don't think that can be the culprit for the amount of oil I have over the rear end of the bike.

I'm sure that many, many owners will have had similar problems, I have got ATY but FYO was out of print and I'm waiting for a new copy. Hopefully Forum Members can point me in the direction of some basic things to check?

As one question - crankcase fixings - I have torqued down the heads after the bike has been through several thermal cycles, what about the crankcases - are there any studs/fixings that should be checked for tightness now that the bike is along the running in path?

Any advice much appreciated - I know it's not a problem for it to drop a little oil but from a personal point of view I was brought up to believe a Vincent properly put together should be oil tight. I'd quite like mine to be one of those if I can manage it.........

Oh - I did get it up to 90 something today for a quick spurt on the flat after I'd been riding 70 miles, and did over 100 in total so it was thoroughly warm and oil as near working temperature as it is ever going to get.

I guess there is about a teaspoonful in total spread across three distinct puddles now on the garage floor having let it sit an cool down for 4 or 5 hours.

I'm running 20/50 mineral oil in the engine. Oh - and I'm not going to fit an elephant breather thanks - just can't get around the look of them. I've read MPH at length about the two types of breathing system and having to shut down the timed breather before moving to a D type off the front rocker cover on the basis the two breather systems are mechanically incompatible, don't fancy going down that road either.

Thanks for reading...


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Well Known and Active Forum User
VOC Member
oil leaks

Hi B.L. One possibility is the valve lifter. Even with new seals if the cable is tight. Ensure there is some slack in the cable to allow the seals to do their work. At least it will be one more possibility eliminated.:confused:


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Would you get enough out of the lifter to coat the back end nicely?

Hi DJ,

Thanks for this - I am currently investigating with VinParts about a fix they may have which the Forum told me about. I'll see what the score is there.

I've just spent half an hour with the bike up on the ramp and a lamp underneath looking, looks very much like lower part of the engine, below the battery tray, the rear crankcases above that are clean and tidy - the oil seems to be spraying/collecting from low down around then and on/around the electric starter. It is definetely engine oil though.

Will progress the lifter idea - I reckon it is likely to be one of those things were you do things one idea at a time and, with luck, get there.

Nothing is looking obvious to me - I am wondering if there is a need/opportunity to nip the crankcases up similar to the way the heads needed torquing down once the bike had been through a few warm up and cool down cycles.



Vic Youel

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Non-VOC Member
Hi Stuart,

I would leave those 5/16 inch dia long crankcase bolts well alone; you could get yorself into trouble there. There are quite a lot of them and you cannot easily access both ends. Sounds like the exhaust valve lifter entry point; there is a mod with and extra rubber seal. I'll have a look for it and send it to you.

The breather has always been recognised as rather inadequate and with spirited riding a tea spoon can make a real mess. I live with much worse leaks and tell critics that it helps prevent corrosion!! From memory, there are some early MPH articles about sharpening the slot in the timed breather to make a little improvement.

One rider in your section has made an excellent mod using a Ducati breather that is out of sight; much nicer than the one time ubiquitous elephant trunk of the eighties.

By the way the gearbox level should be just up to the bottom of the stick; any higher and it stands a risk of leaking through to the clutch eventually...... also check the chaincase oil level now and again because crankcase pressure can push up the oil level and again eventually cause clutch slip when it gets past the seals.

All the best

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