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PD: Primary Drive Oil Leak


New Website User
VOC Member
I have a 51 Rapide that is leaking oil where alternator face fits into primary chain casing. I recently picked up the bike after having it restored by “ someone”. He said the alternator face is smaller then the original ones used ,so I needed to make a plate to go between alternator and case. So that is what I did and yes noticed a gap as a took items apart. The plate seems to have worked for awhile but now have oil dripping again. Anybody with experience on how to solve this leak ?


Well Known and Active Website User
VOC Member
On my Twin, I have a doughnut of 1/4" thick closed cell foam. On some bikes, that spot seems to be needed for the primary case to breathe, but on a Comet the area where the gearbox shaft sticks into the case is open enough for plenty of breathing. On another thought, could your leak be there?

Bill Thomas

Well Known and Active Website User
VOC Member
Make sure you don' have too much oil in there,
Worth checking the oil levels in the gearbox , Primary chain case ,
And the oil tank OFTEN, It' s been known for oil to come from the gearbox and over fill the chain case,
And also from the engine to the chain case,
These are old Bikes and things need checking as often as poss',
I check mine before most rides together with tyre pressures,
Modern tubes tend to leak air in a short time ?.
Good Luck, Bill.

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