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Misc: Everything Else Comet: primary chain oil leaking out mainshaft hole behind clutch

RapHRD

Website User
VOC Member
I'm sure this has been discussed plenty of times before, but how do you seal off the hole in the inner primary cover that the gearbox mainshaft goes through to prevent primary chain oil leaking out?
 

b'knighted

Well Known and Active Website User
VOC Member
Remove the level screw in the cover to drain the oil to the correct level.viewing the oil through the filler cap should let you see that the bottom of the lower run of chain is touching the oil enough to lubricate the chain. The visible oil should be fairly clean, very similar to the condition of the oil you put in.
If it is conterminated with engine oil it is probably a result of the engine dumping while parked, then crankcase pressure pumping this oil through the main bearings.
 

RapHRD

Website User
VOC Member
I'll try to better explain my question.

The hole in the inner primary cover that the gearbox mainshaft goes through is oval shaped to allow the gearbox to be adjusted forward and back. So the mainshaft isn't an oil tight fit through this hole. Is there a way to seal this hole so there's no oil flying out when the bikes running?
 

Dave Hulstone

Well Known and Active Website User
VOC Member
I guess what we are trying to say is this is a known problem area with the Comet set up regarding oil leaks. As you know, the adjustment slot cannot be sealed up to stop splashed up oil escaping via the main shaft, or it ceases to be an adjustment slot. There are some experienced Vincent fettlers like Greg Brillus or Ken Phelps for instance, out there who successfully manage to cure this by fashioning some sort of disc that fits perfectly around the shaft but isn’t fixed, allowing adjustments to still take place. These can be made from a flattened coke can amoungst other things. Ken did a write up on this once in MPH.
I think the other guys are referring to keeping the oil level spot on so making sure no oil is coming in from the engine and also making sure the primary chain case isn’t becoming pressurised? Mine is in with Mr Brillus as we speak getting sorted, which he has successfully done before but I’ve since had an Alton electric starter kit fitted by a non Vincent wise mechanic and it now chucks oil out constantly, or it did until I drained it completely in frustration and took to oiling my chain with chain lube through the filler hole. Not ideal I know, and I risked overheating my Conway (Honda) clutch.
I hope some of this helps.
 

Bill Thomas

Well Known and Active Website User
VOC Member
The bottom end has been together since 1977,
Used for road and raced when the twins went bang !!,
Standard gearbox and clutch,
Super little Bike, Just wish they were little faster,
Can't see why they were not made as 600 cc, Like a Panther ?.
 

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b'knighted

Well Known and Active Website User
VOC Member
Oil pulsing out of the hole is a symptom of the problems I described. Sealing the hole will give you a different problem.
There is a different source of slight oil drips in this area as both the Comet breather pipe and the chain oiler deliver to this area. The drips and dribbles that these may produce are very slight compared with the half pint pulses that a descending piston can blow out of an over full primary chaincase. I have only experienced the pulsing oil overflow once and it was completely cured by draining the crankcase and primary chaincase, curing the slumping and starting again with a correct chaincase oil level.
 

Dave Hulstone

Well Known and Active Website User
VOC Member
I have my breather and chain Oiler pipes connected to 2 pipes running to the back of the bike. I can tell my problem is eminating from my primary chaincase because the oil leak is atf red.
 

Dave Hulstone

Well Known and Active Website User
VOC Member
The bottom end has been together since 1977,
Used for road and raced when the twins went bang !!,
Standard gearbox and clutch,
Super little Bike, Just wish they were little faster,
Can't see why they were not made as 600 cc, Like a Panther ?.
I agree William. If I hadn’t converted mine to a 600 I don’t think I’d use it half as much. I remember when I first rode it in anger, not just to work and back, in 07 around the tt course chasing my dad on his Shadow, I thought what a sweet handling bike. If only it just had another 10horse power....
 

manxman

Website User
VOC Member
RapHRD, see issue 37, page 20 of the Oz Vincent Review. This covers the Ken Phelps solution to your issue (a simple flattened bit of aluminum from a Coke can, as mentioned above). MartynG was kind enough to point me this direction in an earlier thread. Hope it’s helpful.

I have similar issues with my Comet. Will resolve this winter and intend to use this method.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Well Dave , You have solved your own problem !!,
Don't use ATF, It's too thin !,
Should be engine oil.
I was timed on my Blue Road Comet at 99.8 mph On a flying 1/4 mile once,
But I nicked the cylinder head and 36 mm Dellorto Carb off my Special.
 

vibrac

Well Known and Active Website User
VOC Member
I have electric start on my Comet a mainshaft/chaincase oil seal and a Honda Clutch the level is correct and I have not noticed a leak.
The real answer is like my Flash and Comet Racer a belt drive unfortunately that's not possible with an electric start (yet!)
 

greg brillus

Well Known and Active Website User
VOC Member
Hmmm I almost look for a dark corner when my name is mentioned.......... With the newer electric starter kits the machined hole through the inner primary cover is slightly larger than the original oval ones. My guess is that it was easier to simply machine a round hole than program the CNC mill to cut an oval one. The good thing is the surfaces are nice machined alloy.......I'm not familiar with this 'Coke can trick" but I found an easy way is to measure quite accurately the distance gap from the case hole to the back of the large hardened clutch shaft washer, probably around the 2mm mark.......and make up a nice disc shaped washer from rubberized sheet cork, then glue this to the back of the steel washer.........remember that the shaft does and needs some end float, so don't make the disc too thick, it just needs to kiss the alloy housing of the inner primary cover and create a seal......... I carried out this mod not so long ago on a prewar Comet and it worked well........On that particular bike I did use ATF in the primary as using engine type oils was too slippery and i could not stop the clutch from slipping.........This is where ATF should be used if the clutch strength is marginal.
 

MartynG

Well Known and Active Website User
VOC Member
Well Dave , You have solved your own problem !!,
Don't use ATF, It's too thin !,
Should be engine oil.
I was timed on my Blue Road Comet at 99.8 mph On a flying 1/4 mile once,
But I nicked the cylinder head and 36 mm Dellorto Carb off my Special.
I was having issues with clutch 'sticton' or drag with my clutch. After consulting the experts in clutch friction materials at EBC in the UK I was told by them that ATF should NOT be used in a motorcycle clutch as will cause the formation of gums on and IN the friction material and the only fix is to replace with new, not ATF contaminated bits.

Their recommendation is to use a motorcycle specific transmission oil, they mentioned Motul TransOil 10W30 and I have used it ever since.

For info I have attached the latest instructions for setting up a 'conways' honda clutch in a Comet.

Martyn
 

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