Does anyone know why the primary is driven by a chain, requiring oil for lubrication verses a belt driven primary without oil?

How difficult is it to convert the primary from chain to belt drive and can a belt driven primary be used with the stock enclose outer covers?

 

Harley fitted primary belts on their very first belt-drive bike, the Sturgis, but for some reason never used it on other models. My guess is the primary has to soak up crank-shaft torque fluctuations and reversals that a belt is less suitable for than a chain. Also a chain running in an oil bath is very efficient in transmitting power, possibly better than a belt and perhaps the clutch gets cooled by the oil.

Another factor is the stock primary reduction ratio is not very great, so there is not much room for a belt, unless it is wrapped around the clutch drum, when it starts taking up a lot of space. I think an enclosed primary belt would need a much bigger primary casing.

That's the best I can offer!

 

Bingo....the total combination with the compensator & wet clutch is better served by a wet lubrication system with chain. If you don't believe me run without the compensator on a bike. It will rattle your frickin teeth out. And dry belts can get really hot.

 

Had a 81 FXB loaned to me for a while , those belts popped all the time. If you had a motor that was making more power than stock it was a ticking time bomb. Even stock power level heat would just kill the belt. Enclosed belt from the factory, many tried getting air into the primary by spacing out the outer primary out from the inner and also milling slots into the inner primary and using vented inspection covers. They(new belt) would last for a long enough time after whatever fix you tried to trick you into thinking " We got it this time" and then when you hopped on it and shifting into 2nd BAM it would break again.

 

Harley tried very hard to make the belt-drive primary work. Gates Rubber never could come-up with a belt that would stand-up to the heat and torque issues involved inside the primary case. Thus...it never got past those couple of years and models they tried it on. I had a Softail that I converted to belt-drive and it was smooth as silk....lasted about 1,000 miles before the belt went.