Standard Gearing

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

Postby greasemonkey62 » Mon Sep 22, 2014 8:43 am

My model 31 has all the standard gearing as in 23 teeth engine, 42 clutch, 17 gearbox and 42 rear wheel, yet at 50mph plus it seems it is over revving and I am loath to go any faster not wanting to rev the old girls engine too much, I have sometimes even looked for another gear when I am already in fourth, I have thought of fitting a 19 tooth gearbox sprocket, has anyone tried this? if so did it make starting off from stationary a problem due to too high gearing??

Cheers Ray.

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Re: Standard Gearing

Postby dave16mct » Mon Sep 22, 2014 10:13 am

I know what you mean but I would think going higher would make it difficult to ride in town. You already have a higher gearbox ratio (16 is standard). You might need to do a lot more gearchanges on hills too.
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Re: Standard Gearing

Postby saltbox alf » Mon Sep 22, 2014 10:32 am

The gearing is correct, are you getting some clutch slip, had this problem on my Sp'rocket, not noticible as full slip, but made it seem as if it was over revving when giving it some beans!
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Re: Standard Gearing

Postby 1608 » Mon Sep 22, 2014 12:40 pm

16T is standard for the gearbox, 17T was fitted to the csr. I fitted an 18T to my G12 DL and it was too high. I went back to 16T and accept that this is the optimum gearing and not to be afraid to give it some revs as was its design. You just can't try and compare these oldns with more modern machinery. Also, not being as smooth as a more modern bike the oldns seem more revvy than they actually are when ridden. One might get away with 17T if one is on the slim side, but I'd stick to the original gearing as the bike is far more tractable and the engine will last longer too. 19T will be far too much.

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Re: Standard Gearing

Postby robcurrie » Mon Sep 22, 2014 4:28 pm

My CSR had a 17 T originally, but being a lightweight and living in an area that has no big mountains, I fitted an 18 T. Pull away is effortless and on the open road I sometimes also look for 5th gear!

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Re: Standard Gearing

Postby greasemonkey62 » Tue Sep 23, 2014 10:14 am

Hiya, no there is no clutch slip I am just looking for 60mph at lower revs, and thought someone may have tried a 19 tooth sprocket on the gearbox final drive, and I could have had first hand feedback on the effect the fitting of it had on pulling away from stationary.
I understand the model 31 had a maximum speed of in the 90's, with standard gearing the motor must have been really buzzing.

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Re: Standard Gearing

Postby saltbox alf » Tue Sep 23, 2014 12:02 pm

I would have thought so too, catch the pistons on their way out and a visit to the dentist for loose filings. no doubt you could get that fast, but on 50/60 year old machinery!!! :shock:

No I understand your point re cruising speed but the higher the gearing the more load on the clutch round town, my CSR don't like towns at the best of times and that is just one tooth up on the cooking model.
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Re: Standard Gearing

Postby petert120r » Thu Sep 25, 2014 2:41 pm

Just been out on the G12 CSR with exactly the same gearing as you and at 60/65mph didn't feel "busy" at all. At a loss to explain your symptoms other than what has already been suggested i.e. clutch slip, which isn't easy to sense. Have you tried pulling the lever and releasing it quickly at around 50mph in top under load such as a gradient? It should bite firmly immediately, not over a couple of seconds or so.

I had something similar with my Bonnie a few years back and cured it by fitting new clutch springs.

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Re: Standard Gearing

Postby 1608 » Thu Sep 25, 2014 3:45 pm

But, Ray's bike isn't a CSR. If it was as simple as just fitting a larger gearbox sprocket then the factory would have done so. These twins are designed to be a bit revvy. As I said, 18T was too higher geared on my G12, especially in the lower gears. This 'busy engine' syndrome is experienced by most people when getting back on old machinery, or those that have become used to more modern bikes. Try it by all means, but for 19T I think you may have to lengthen the rear chain.

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Re: Standard Gearing

Postby bigjohn » Fri Sep 26, 2014 8:41 am

Hi everyone - see my previous threads regarding twin carbs. This problem is exactly like I had, straining in the gears and not revving out in the gears especially top. My bike sounded very busy at 55mph even though it was not revving out. It would only go about half as fast in every gear. I know yours is a single carb but are you sure it is actually revving to its maximum. You never know it might be the same problem. Just a thought.

John.

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