Belt drive to a Dommie 650

If you have checked the mainshaft with a dial gauge and there is zero or very little deflection e.g 0.0005" then the problem could be with the clutch hub. Try putting the old hub on and see if the run out still exists. If it does have a look at the sleeve gear bushes and mainshaft bearing.

I purchased a belt drive conversion, for my 650, from the Norvil crowd back in 1998. In those days it came advertised with comforting words implying that it was easy to fit and that no additional engineering would be needed to achieve this. Load of tosh....A week of grafting, several phone calls and changes to my bike finally got the beast working....but not very well. The first problem was the belt was 20mm too long. To achieve the correct free play, in the belt, meant moving the gearbox all the way backward which it could not do until I filed slots in the engine plates. With the geabox that far backward, the clutch drum then fouled the outer case because the bulge did not cover the clutch. The rear chain was now too long and had to have a link removed. The clutch drum itself was oval and also wobbled on the gearbox mainshaft because the specially madespline adapter was not a close fit.

Adding to the misery... once up and running I found the belt gearing too low for a 650. I was hitting 70 mph at over 5000rpm. This meant changing the 19 tooth gearbox sprocket for a 20T, which meant pulling all the new bits off to change the sprockets and then having to add a link to the rear chain. Madness!!!

I was so cheesed off that I wrote a lengthy article for Roadholder about the fun and games. Please read it and those from other DIY members. They can be found in the Technical Section.

Thankfully, the kits supplied now days are much better made and often truly ready to fit.

The big message.....there is much to be gained with a belt drive conversion but you must ensure that your gearbox has the minimum of wear in its bearings and bushes and make sure the belt runs on a shaft that is parallel to the crankshaft.

Previously phil_hannam wrote:

The big message.....there is much to be gained with a belt drive conversion but you must ensure that your gearbox has the minimum of wear in its bearings and bushes and make sure the belt runs on a shaft that is parallel to the crankshaft.

I don't think there's much wrong with the original chain, but I do strongly agree about alignment. Very important for chains, but essential for belts.

All that grief when there is nothing wrong with achain! Yes, madness !!!