It is intriguing that the C Comet has a wacking great hole in the back of the chaincase to allow for the gearbox to pivot for chain adjustment. Neither of my Comets with standard breathers leak oil (from there, that is!).
Dynamo/Alternator
- Thread starter pifinch
- Start date
I agree Hugo.My Comet does not leak from the chaincase.I thought the leak I had was from the dynamo seal as my pillion gets her right boot nicely preserved with oil,on removing the dummy shaft for my alternator drive there was no oil behind the seal.I rebuilt the gearbox with new gaskets as I had to take out the box to fit new seals to the valve lifter,and readjusted the timing of the breather at the same time.Time will tell if the leaks are reduced,although the leak only shows up if I cruise at 60+.There is some discussion on Vincent.com about breathers that run at negative pressure until higher revs are used and then they start to blow.If the changes that I have made don't work i'm going to try a PCV valve.Any suggestions for a nice neat one anybody?.I'm not keen on elephant trunks they look better on Elephants
Comet Oil Leaks
It is very difficult to pinpoint the actual source of oil leaks as the wind flow under the bike follows some very strange contortions that seem to defy logic and often bring the oil forward rather than back. The usual suspects include the chain oiler, the valve lifter mechanism, the oil pump end cap and the grub screw sealing the oilway drilling at the bottom of the crankcase. This last is difficult to seal in situ as it is has a head of oil behind it. However on Comets it seems to be mostly the Burman gearbox. The kickstart and gearlever shafts and the clutch adjuster are all below the level of the mainshaft and when everything is spinning, oil and grease is chucked everywhere. I had mine rebuit with oil seals on the shafts but if I add any oil to the box, (it is packed with Sperol semi fluid grease) for the sake of the layshaft bearing, the oil soon reappears on the outside. There is also a core plug on the inboard end of the layshaft which is difficult to seal and is sometimes missing altogether. Mr. Burman's philosophy regarding gearbox lubrication seems to be lost in the mists of time. The works recommended a grease/oil mixture which I believe led to some interesting fires when they boiled up the concoction in order to fill the gearboxes.
It is very difficult to pinpoint the actual source of oil leaks as the wind flow under the bike follows some very strange contortions that seem to defy logic and often bring the oil forward rather than back. The usual suspects include the chain oiler, the valve lifter mechanism, the oil pump end cap and the grub screw sealing the oilway drilling at the bottom of the crankcase. This last is difficult to seal in situ as it is has a head of oil behind it. However on Comets it seems to be mostly the Burman gearbox. The kickstart and gearlever shafts and the clutch adjuster are all below the level of the mainshaft and when everything is spinning, oil and grease is chucked everywhere. I had mine rebuit with oil seals on the shafts but if I add any oil to the box, (it is packed with Sperol semi fluid grease) for the sake of the layshaft bearing, the oil soon reappears on the outside. There is also a core plug on the inboard end of the layshaft which is difficult to seal and is sometimes missing altogether. Mr. Burman's philosophy regarding gearbox lubrication seems to be lost in the mists of time. The works recommended a grease/oil mixture which I believe led to some interesting fires when they boiled up the concoction in order to fill the gearboxes.