18cs?

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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dave16mct
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Re: 18cs?

Post by dave16mct »

You need to fit a brake torque arm pointing forwards.
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Groily
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Re: 18cs?

Post by Groily »

see pic. This one's a '54, but same arrangement.
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Heleander
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Re: 18cs?

Post by Heleander »

Well, maybe i just should let it be...
Groily
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Re: 18cs?

Post by Groily »

Hmm. Actually, I don't think you should leave it, because the arm is designed to take the load one way only.
I am told - and I believe it - that it is potentially dangerous to have it on the wrong way.

The hassle is that you need to find another torque arm, I realise . . . and that is definitely a pain. But all the same . . .
Heleander
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Re: 18cs?

Post by Heleander »

Hmm.. the hole for the torque arm is where it is and designed to be that way around as far as i can understand. I don´t see how i can turn the wheel to make it fit the way you suggest. Maybe i just don´t get it...
Groily
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Re: 18cs?

Post by Groily »

You can turn the wheel / brake backplate - but you need a different torque arm that is the 'other hand', almost a mirror image, so that the long flat section goes forwards, with the bit for the adjuster in exactly the same place as on your one. There are two types.

The same bolt goes into the same steel insert in the hole on the alloy brake backplate, but in front of the fork leg.
Then, the cable goes straight on down to the lever on the brake, which would sit at a less acute angle than yours does now, with its pivot just to the rear of the fork leg.
That way, the geometry would be correct and the brake would be more efficient (within the limits of these things that is!) and above all, it would be safe.

Having said all that, it is quite a common thing to see them set up the wrong way round, and I don't personally know anyone who has suffered a catastrophe. But, as I said, I am told the risk is there and I think the 'prudent owner' if there is such a thing, would not tempt fate! Others on here know more and may have more to say on this . . .

It's worth noting that on some of the later machines, the lower part of the flat section was made much more substantial, on CSR models, P11s and things like that - so it must have been recognised as a potential point of weakness even if properly assembled.
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Joker_Bones
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Re: 18cs?

Post by Joker_Bones »

I guess the issue is... the way it is set up the torque arm is acting in compression. Being a flat bar it is not the ideal shape to resist axial compression, it will bend/buckle before the full strength of the steel is reached. If fitted forwards it will act in tension, then the full strength of the bar can be utilised as it is being pulled not pushed and cannot bend or buckle.
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dave16mct
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Re: 18cs?

Post by dave16mct »

Spot on JB.
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Heleander
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Re: 18cs?

Post by Heleander »

Thank´s for great info. Got to find a different torque arm then. My guess it´s a -56 hub for the tucked in leverarm i have. Wonder in what setup "my" torquearm was used?
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dave16mct
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Re: 18cs?

Post by dave16mct »

It's for pre '53 which had the adjuster and cable behind the forkleg and the lever pointing backwards. Previous owner has bent the adjuster to suit.
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