Information relating to the Matchless G15 or AJS Model 33 750cc twin. This also includes the G15 Mk II and the G15/45
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Postby schwantzz » Wed Jan 04, 2012 10:24 pm

Whilst I'm in the process of replacing the main crank seal behind the primary drive sprocket on my 67 G15CS I was wondering if I ought to make any changes to the gearing.
The Engine sprocket is currently 21T, Clutch is 42T (I haven't counted the gearbox or rear wheel yet but assume std)

What gearing do other owners run for road use? I have a trip in the summer with a fair few miles to cover. The bike was previously used with a sidecar and my father had noted that the standard gearing was fairly low and good for sidecar use so I am wondering if it will be too low for solo?

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Postby bjork » Thu Jan 05, 2012 12:40 pm

Depends what gearbox sprocket you have. On my G15CS, I used to swap between a 21t crank sprocket and a 22t, depending on wether I wanted lively acceleration with a still decent high speed or a more relaxed high speed e.g. for the Poland via Calais trip mainly on Motorways and A-roads.
If it felt like sidecar gearing on a 21t crank, then maybe the gearbox sprocket is too small? Sure mine was 19t?
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Postby John Donne » Thu Jan 05, 2012 8:20 pm

For the American market the G15CS was fitted with a 17 tooth G/B sprocket. The road models used a 19t G/B sprocket. The G15CS used a 21t engine sprocket, and the same clutch and rear wheel sprockets as the Atlas, as all the G15, N15,33 MODELS. The G15CSR's used a 22t engine sprocket. For every day use, use a 21t engine, and a 19t G/B and your G15CS will work finE. You CAN always try a 20 G/B sprocket, as this will mean you do not have such high revs for your speed. The American market was always about 1/4 miles times, and that was the main concern of the owners, or what would it run in the quarter mile. Magazine road testers at that time always took their bikes out to a drag strip. The first road test of the Atlas Scrambler was run down, i think a drag strip in Pamaona.

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Postby Ludwig » Tue Jan 10, 2012 8:29 pm

The pre-owner of my G15CS fitted a primary belt drive. Pulley 29, clutch 55, gearbox sprocket 20,
rear wheel 42 teeth. So the overall ratio is 3.94 in top gear, in third gear 4.8.
The original ratio is 4.94 in top gear. Very comfortable to cruise at max. allowed speed (100km/h) with
about 3250 rpm. Disadvantage is the need to use the third gear in towns.
Regards Ludwig

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