Belt drive of unknown brand

lcrken said:

I thought we had established some years ago that the belt primary drive doesn't really provide any more shock absorbing than a chain primary. The real benefits of the belt drive are less weight, dry clutch, and the ability to easily run a higher primary drive ratio.

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This is also my opinion. But it isn't easy to increase the ratio when using an original altonator. There is little space to increase the outer diameter of the sprocket on the engine. Then it is only possible to reduce the OD on the clutch basket.
Norman White can deliver this. Are there any other alternatives to increase the ratio with original primary cover and altonator?

Ken and Kvinnhering:
I don't know for sure about shock absorption - just what I heard. The quote below is from a Gates technical advisor but he could be referring to final drives and not primary drives. And his advice doesn't prevent people from doing what they need to do. It depends on how much value the advice of "technical experts".

"I wouldn’t recommend the use of our industrial Poly Chain belt on a motorcycle application given the modulus is so high that there is little give under fluctuating loads. We manufacture aftermarket belts specifically for the motorcycle industry and these have special constructions and tooth profiles that are designed for the loading these drives will see."
John Anthony


Belt Drives LTD

Kvinnhering said:

This is also my opinion. But it isn't easy to increase the ratio when using an original altonator. There is little space to increase the outer diameter of the sprocket on the engine. Then it is only possible to reduce the OD on the clutch basket.
Norman White can deliver this. Are there any other alternatives to increase the ratio with original primary cover and altonator?

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I think you are right about that. Up until recently, all my experience with Commando belt drives was on race bikes with no alternator, so size of the front pulley wasn't limited. I usually ran a 1.75 drive ratio (40T/70T) with the Newby drives, and 1.78 (36T/64T) with the Norman White drive, compared to the stock Commando 2.19. Norman also made smaller clutches. The tallest ratio set I have from him is a 33T/60T pair that gives you a 1.82 ratio. It was used on a race bike without an alternator, so I'm not sure if the 33T pulley will fit with the stock alternator. If it does, that would be a good combo for a Commando. I'm now fitting a belt drive to my MK3, and had to make a new alternator mount to have room for a larger front pulley, as well as a custom cover for clearance.

Ken

Hi Ken

Thats of intrest Ken. I went from 34 to 36 then 38 on the front! I have not seen a 40 tooth produced or advertised. I have clutch baskets of 68 70 & 72 teeth. I run the 36/38 front & 70 rear all Maney parts, the odds I have picked up on the way. My front pulley for the Rickman needs replacing & I have a triumph Newby front pulley with 39 teeth. I will get that machined & try that. Engines a 750, what cc was your set up?

Thanks Ken.

all the best Chris

Chris said:

Hi Ken

Thats of intrest Ken. I went from 34 to 36 then 38 on the front! I have not seen a 40 tooth produced or advertised. I have clutch baskets of 68 70 & 72 teeth. I run the 36/38 front & 70 rear all Maney parts, the odds I have picked up on the way. My front pulley for the Rickman needs replacing & I have a triumph Newby front pulley with 39 teeth. I will get that machined & try that. Engines a 750, what cc was your set up?

Thanks Ken.

all the best Chris

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I got the 40 tooth pulleys from Bob Newby. They were all for 40 mm wide HTD belts. I've run the 40/70 combo on both 750 and 920 bikes. I ran the Norman White 36/64 (also 40 mm width) on the 750 Commando/featherbed road racer. When I switched it to a landspeed racer with a 920 on nitrous, I changed to a Newby 40/70 setup. I tried the Norman White kit once on my 920 powered PR, and it didn't hold up (sheared teeth), so I went back to the Newby setup. The 33/60 Norman White setup was used on the Commonwealth Norton road racer, a Caffrey chassis with 878 cc Commando engine. As far as I know, it never had any belt problems.

Ken

Well there a multitude of opinions here (as usual) We selected the Poly Carbon chain for the CNW Electric Start Conversion almost 3 years ago. And, the engineer at Gates, that we were working with, recommended the belt we are using. Aside from varying opinions, we have 3 years and over 100 kits installed around the world. As of now I have not been informed of any belt or transmissions failures. In our own in house testing, we have an Interstate with the starter installed that has over 3500 starts and 5000 miles. The Interstate is used for a variety of road tests, and at every stoplight, stop sign, or traffic stop, the engine is stopped and restarted. Additionally we run the same sprocket / clutch basket and belt that are in the kit on two separate Commando race bikes. Been running the system for 2 years of racing with no belt, or transmission failures.

So there are opinions and there is real world, product test data. I normally go with evidence and not opinions

jseng1 said:

Where is the rear wheel polybelt kit? There's a project for you G81 Can Cycle. Send me one that fits and I'm be happy to test it for you (so would everyone else).

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Untitled by swooshdave, on Flickr

DIY kit!

The Poly Chain Carbon looked good to me too, and I would have liked to use it on the MK3 I'm currently building, but can't. I'm using mostly parts from the Old Britts electric start conversion, and the pulleys have the conventional HPD tooth shape. Gates says that the carbon belt needs to have the newer tooth profile pulleys, and is not interchangeable with the HTD design. At the moment, it looks like CNW are the only ones offering a Norton kit with the GT2 tooth profile to suit the carbon belts (as well as the PowerGrip GT3 belts). At least I assume that's the tooth profile they are using on their pulleys. If I ever do another electric start conversion, CNW are the ones I'd go with.

Ken