WD Motorcycle forum

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Dec 13, 2014 - 8:18PM

M21 gearing

Tried the search function but no luck with my question , sorry folks .

The bike i'm working on pulled a sidecar with a 45 rear sprocket , i now have a new 42 tooth rear ,

Just wondering if the gearing now will be satisfactory for general use + some longer trips, i have -

19T Engine sprocket
43 Clutch
19 gearbox
42 rear

From what i can workout this seems pretty much standard with maybe a 20 engine sprocket as another option for a 21 , what do you reckon ? .

Ian Wright

Dec 13, 2014 - 8:23PM

Re: M21 gearing

20T is the standard engine sprocket for an M21...(source BSA parts list M Series 1949-54)....Ian

chilly

Dec 13, 2014 - 8:52PM

Re: M21 gearing

Thanks Ian , checked the parts book once again , yep ! i read it wrong , dohh !.

Gary Owen

Dec 14, 2014 - 8:07PM

Re: M21 gearing

chilly

Thanks Ian , checked the parts book once again , yep ! i read it wrong , dohh !.

My parts book (M Models 500cc and 600cc 1949-1958) says a 19T sprocket (65-3506) is the right fitting. I need to know myself as the sprocket needs replacing on my '58 M21. Am I using the right parts book?

Gary.

email (option): gj.owen@hotmail.co.uk

Ian Wright

Dec 14, 2014 - 8:20PM

Re: M21 gearing

The original post was about the various sprockets but the engine sprocket listed was incorrect at 19t..

The 49-58 parts book gives 20t for the M21...65-2538 and 18t for the M20 ...67-1132.

65-3506 is the gearbox sprocket which is 19t...Ian

email (option): ian@wright52.plus.com

Gary Owen

Dec 15, 2014 - 6:06PM

Re: M21 gearing

Ian Wright

Your dead right - of course... Got gearbox and engine sprockets mixed up!
Gary.

email (option): gj.owen@hotmail.co.uk