Standard Gearing

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Re: Standard Gearing

Postby dave16mct » Thu Aug 25, 2016 7:40 pm

16T for a standard road bike is standard. 17T standard on a CSR. How can fitting a 17T lower it?
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Re: Standard Gearing

Postby mumbray » Fri Aug 26, 2016 4:37 am

where do i find a 24t engine sprocket

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Re: Standard Gearing

Postby 1608 » Fri Aug 26, 2016 11:10 am

I tried fitting a larger g/box sprocket on the G12 and found that the acceleration suffered and not a lot of noticeable drop in engine revs when cruising. The bike didn't feel as tractable as when on standard either. Some people seem to get away with it, or perhaps just kidding themselves, but I'm pretty sure the factory fitted the optimum gearing to compliment the model. These twins are designed to rev, and admittedly do feel busy when being ridden, but I believe its more of a perception. All bikes old or modern Rev relatively quickly, thats what gives them the acceleration. Higher revving is far less damaging to an engine that labouring. Thats my take on it anyway.

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Re: Standard Gearing

Postby Groily » Fri Aug 26, 2016 1:24 pm

I'd agree that the factory fitted what was optimum back then, but there wasn't a lot of dual carriageway, much of the 4 wheeled traffic could barely wheeze past 70mph, and was out-performed by even modest 250s in typical driving. I remember even my old C15 could seem fast compared to some of the jalopies out there!
But with lorries now cruising at a regulated 55+mph up hill & down dale, with cheap cars having better accleration and vastly higher all-day cruising speeds than even quite sporty bikes of the 50s and 60s, my money's on gearing up a bit so one can cruise stress-free with at least the slower traffic on open roads.
One tooth on the g'box reduces revs by about 6% going from 16 to 17T, the final effect depending on tyres etc. Running a 19 instead of a CSR's 17 reduces rpm by about 12% which is useful, as 55mph becomes 62, and 62 becomes just under 70, which is a handy enough modern speed. Which suits me fine as one blessed with open roads and little traffic, but wouldn't suit everyone - and wouldn't suit me either if I lived in a town probably. 3rd is good for any speed that's legal virtually, so not a problem maintaining momentum if one's happy to change gear now and then.
The downsides, as discussed, are it's slower off the mark (but only to about 20mph), harder on the clutch, and takes more road speed to balance electrical loads. But the upside is you get to places at quasi-modern speeds without revving the engine much. 30 in first, 45 in second and 55-60 in third in non-aggressive riding. Yes, they like revs, but there's also a pretty direct relationship between sustained high rpm and general mechanical wear and tear.
As to where to get a 24T crank sprocket, I got mine from Steve Surbey at AMC Classic Spares in 2013.
Now . . . a five speed cluster . . . that would be very nice - at a price!
But in the end, it comes down to where you live, what you want a bike to do, and what sort of riding you enjoy most.

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Re: Standard Gearing

Postby mumbray » Tue Aug 30, 2016 2:07 pm

amc spares don't have a 24t engine sprocket available anymore,i had already bought the 17t gearbox sprocket by time i read all of these comments.i will leave it till i have the motivation to fit a 19t gearbox sprocket,cheers for the advice anyway.

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Re: Standard Gearing

Postby SPRIDDLER » Tue Aug 30, 2016 4:18 pm

You could try these folk who are very well known and active in the classic bike world for sprockets...........

http://www.sprocketsunlimited.com/Index.html
I poke badgers with spoons.

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Re: Standard Gearing

Postby dave16mct » Fri Sep 02, 2016 11:15 pm

Andrew Engineering stock the 24T engine sprocket 028479 £44.40.
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Re: Standard Gearing

Postby mumbray » Wed Sep 07, 2016 5:33 pm

cheers for that,they say i got the last one and their not makeing any more,so i was lucky.just hope the bike can pull it with the 17t gearbox sprocket i've already fitted.

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Re: Standard Gearing

Postby mumbray » Sun Feb 11, 2018 7:29 am

i now have a 19t gearbox and 24t engine sprocket on the bike and i think this is perfect.

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Re: Standard Gearing

Postby bilstonbiker » Wed Feb 21, 2018 8:32 am

anyone wanting drive or gearbox sprockets try Norvil

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