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Gearbox oil in chaincase

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Hello. Gearbox oil is somehow getting into the primary chaincase of my 99. Has anyone any ideas why?  

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I have read of excess oil being pumped through the mainshaft, not sure how there is the pressure for it though.

Thanks to you all who responded to my query and for the interesting answers. I've recently fitted a belt drive together with new engine main bearings and seals, so that's how I have noticed this problem. It's probably always happened but got mixed with the chain case oil and leaked out anyway. Also, the gearbox always dribbled from the k/s seal so over time, lowered the level too. the gearbox has new seals too now so I'll lower the level a bit. Wee hole in cap is clear.

Love the r/h centre stand idea. It's a good point too. Why are they mostly on the left?

Thanks again

 

 

 

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Drill a tiny hole in the Box inspection cover,(or clear the one thats there) . Fit the O ring oil seal special clutch nut sold by Norton spares stockists. Park your bike on the centerstand ,not the sidestand.  Check oil level is just below level plug.Even better!, fit a side stand to the offside of the bike , great when the camber is wrong and would drain the oil away from clutch. I am up for that too , anyone done this ?apart from the Vincent?.

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The main cause of gearbox oil arriving inside the primary cover is generally due to a very worn Crankshaft  Oil Seal. As the engine pistons rise and fall, this allows a bellows effect inside the primary cover which in turn sucks oil vapour through the gearbox mainshaft.

Another possible cause is a loose bolt(s) by the front sprocket also allowing the pistons to push / pull oil vapour around the various innards.

Various third parties sell expensive oil seal kits to fit on the G/B mainshaft. Try renewing the crankshaft oil seal first.

 



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