CP Layshaft bushes

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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CP Layshaft bushes

Postby ELPS » Wed Sep 13, 2017 8:32 am

Enclosed is a photo of my gearbox layshaft. Should the bronze bushes be a tight fit on the shaft or in the gears? Mine appear to be tight on the shaft. Is that correct? Thanks
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Re: CP Layshaft bushes

Postby zwarts » Wed Sep 13, 2017 12:59 pm

I recently stripped one of the very similar Burman BAP boxes. The layshaft bushes were as yours are, tight fit on the shaft and a running fit in the bore of the gears, so I would say that yours are just fine. As a precaution against possible seizure I would suggest that you fill the box with the correct semi fluid grease rather than any other type. Penrite do a suitable grease for these boxes. Later CP and BAP boxes had better sealing arrangements and could use gear oil!

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Re: CP Layshaft bushes

Postby ELPS » Wed Sep 13, 2017 11:27 pm

Thanks for that. Any idea what clearance they should run? Between the bush and gear that is.

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Re: CP Layshaft bushes

Postby zwarts » Thu Sep 14, 2017 12:12 am

Sorry, can't give you a definitive answer to that one. As these are phosphor bronze, they need a little more clearance than oilite bushes require. In the BAP box which I rebuilt, the gears were a good free fit on the bushes with very little 'waggle' on the gear when assembled. Not very scientific but it is the best way I can describe it!
One observation I would make is that Burman boxes seem to work best when everything has plenty of clearance. Some 25 years ago I rebuilt a B52 with all new bearings and bushes, all carefully reamed to give minimal clearances. It was the worst B52 I have ever used, very stiff gear change action and slow changes. After some 20000 miles it is now quite pleasant again.

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