Belt size

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Jan 21, 2008
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The Caffrey is coming along but I am finding out about it as I go.
Does anyone know what belt size is next up from 920?
The belt drive kit is HTD 8m 920 by 40mm.
I run belts on all my race bikes & I am not happy about the amount of slack I have in this one. All of my bikes are 30mm belts & I like to twist them to nearly 90 degrees. With this 40mm belt I can only get about 60 degrees & there is a lot of distance & alloy to heat up & expand on the primary side.
L:ittle nuggets of info keep popping up.
Originally it was built with a Quaife/Norton box but this was changed for a BSA box believe it or not for the "kickstart".
I now know that my bike was run on the road with a "Q" plate but that the belt drive kit & Norton box have not been used!
The box is right at the front of the adjustment slots & the pullback only has two turns on the nut. So best option is a longer belt as the engine plates have extra holes (for the BSA box) in the wrong place to elongate the gearbox adjustment slot & I would have to make up a longer adjusting rod.
I will update the photos when I can get a on/off switch for my e mac.
(ha ha) ) I am on a borrowed computer!
all the best Chris
Hi Chris,

I'm thinking of running my primary belt (40mm) without any adjustment and I have heard of others doing that too. I have pictures of a Norton racer that show no obvious adjustment and the belt looks rather loose.
Belt size

Your project look real nice.


Hi Jean
When I brought my daytona engine it had a Hayward belt & the previous owner had used a slipper adjuster with the rubber removed!
He could never get the engine to rev & gave up on it pretty quickly.
When I first ran it, it worked fine, however out on the track it missed when you gave it grief. Turned out when revved the pistons closed the gap on the plugs! One copper washer bike sorted!
As to the belt. After the first race it would not restart & felt like it had nipped up. Turned out that when the race finished & I parked the bike up, the belt had welded itself to the polished steel slipper adjuster! I removed the adjuster completely & the belt looks very sloppy but when you come in from a race & look again most of the slack disappears. Rob usually builds his Commando racers with fixed gearbox holes. The Mk4 is to tight but then he did not make the engine plates. When the engine is finished I will swap it for the borrowed engine & elongate the gearbox adjuster slot & drill another adjuster bolt hole. In the meantime I have fitted a 34 tooth front pulley 30mm wide. as I had this for my road
Project. I also have a spare belt. I can twist it through 90 degrees & I feel alot happier about it.
all the best Chris
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