I am away working at the moment and using my spare time to order a few parts needed to get my bike going again hopefully when I return. Before leaving I counted teeth on rear drum twice and came up with 42T. Although there are a lot of 43T drums available for rigid models I cannot find a 42T one. Now I'm wondering if I miss counted ? Can anyone tell me if they did have 42T drum's and if so is it possible to get a reproduction one somewhere. If not, is it possible to get the old one re toothed, and if so, does it cost a small fortune ?
I currently have 20T engine sprocket and 19T gearbox sprocket. If I fitted a 43T rear drum would there a noticeable difference in performance ? Which sprocket is the preferred one for changing gearing on a bike, engine,gearbox or rear ? If I understand correctly, if I go bigger on either the engine or gearbox this will give a higher gearing but I need to go smaller on the rear drum for higher gearing. Is this correct ?
Glenn, you're quite corre…
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Glenn, you're quite correct in your observation. Civilian OHV and SV Nortons used a 42t rear drum sprocket but the War Department models had lower gearing and ran with an 18t engine sprocket and 43t rear wheel. The ex-WD stock was much more common and for some reason, the pattern parts suppliers have stuck with it, although most owners now do much more road work and don't need gearing down for escorting 20-Miles-in-Hour convoys !
I don't think that you'll notice a single tooth on the rear wheel very much unless you're doing lots of fast road work...and if you're a stoutly built chap then the lowered gearing might even help.
If you fit a 21t engine sprocket then that would more than make up the difference.