Gearbox adjuster

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Gearbox adjuster

Postby bob121 » Mon Jun 25, 2018 8:14 am

Hope someone can shed some light on this for me. Started pulling the bike down to address some of the niggles. Got to order a few transmission parts, while compiling the list I remembered the gearbox adjuster. The one one the bike pushes the box forward. There isn't one to adjust backwards to tension the front chain. I've gone through the parts book again and would say that that is correct. There is a slot in the rhs engine plate just behind the top bolt. So it may be possible to retro fit one.

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Re: Gearbox adjuster

Postby McBob » Mon Jun 25, 2018 9:35 am

What you have is correct, the reaction of driving the rear wheel will pull the g/box rear ward. When adjusting the primary chain ensure the top bolt is up against the adjuster, I tapped the box back with a soft faced hammer.

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Re: Gearbox adjuster

Postby 1608 » Mon Jun 25, 2018 1:31 pm

The adjuster is designed to move the gearbox back and forth. Adjust primary chain tension first ( approx 3/8" at its tightest spot) then tighten gearbox fixings. Then adjust rear chain tension ( 1-1/4" at its tightest spot and preferably with somebody sitting on the bike ( off its stand ) because the rear chain tightens up a bit when the bike is sat on.

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Re: Gearbox adjuster

Postby bob121 » Mon Jun 25, 2018 1:48 pm

Cheers. It would just be nice to have an adjuster for tensioning the chain rather than the way it needs to be done at the moment.

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Re: Gearbox adjuster

Postby McBob » Mon Jun 25, 2018 2:15 pm


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Re: Gearbox adjuster

Postby Rob Harknett » Mon Jun 25, 2018 3:24 pm

The tensioner does adjust the primary chain. You do need to slacken of the rear wheel and adjusters, and brake plate anchor so the rear wheel can move forward. Loosen gear box nuts and adjuster. Fit chain and tension via the adjuster, lock adjuster and tighten gearbox nuts. Reset rear chain adjustment etc.. Don't forget you had to loosen the rear brake anchor that also needs re tightening. Plus re adjust brake rod.

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Re: Gearbox adjuster

Postby Mick D » Mon Jun 25, 2018 3:35 pm

Hi

Or you can leave the rear wheel as is and just press down on the secondary chain lower run.

Regards Mick

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Re: Gearbox adjuster

Postby Rob Harknett » Mon Jun 25, 2018 4:20 pm

If fitting a new primary chain, the gearbox would need to move forward, the rear chain will also need to move forward. Any alteration to the primary chain adjustment will effect the rear chain adjustment. You would need the primary chain to be quite loose to ease fitting the primary chain split link.

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Re: Gearbox adjuster

Postby bob121 » Mon Jun 25, 2018 7:12 pm

Thank you all. But there seems to be some confusion. I know how to do the adjustment. The adjuster on this box only pushes the box forward. To tension the chain you slacken the fixings just enough and knock it back. I'd prefer to use an adjuster that pulls and pushes the box. And as new chains are being fitted, now would be a good time to fit a different adjuster if it was possible.

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Re: Gearbox adjuster

Postby Rob Harknett » Mon Jun 25, 2018 8:55 pm

Well the system was used from pre war into the post war years on the bikes. Simply enough to do what it needed to do. In 62 years I have never had a problem. That more than satisfies me. By changing it you would need to declare the non standard fittings to your insurance company. For all insurance there is a question. Has the vehicle been changed from its standard specification.

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