CP Layshaft bushes

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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ELPS
Posts: 39
Joined: Wed Jan 04, 2017 5:11 am
Location: WESTERN AUSTRALIA AUSTRALIA

CP Layshaft bushes

Post by ELPS »

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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zwarts
Posts: 514
Joined: Mon Jan 01, 1990 12:00 am
Location: LANCASHIRE UK

Re: CP Layshaft bushes

Post by zwarts »

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!
ELPS
Posts: 39
Joined: Wed Jan 04, 2017 5:11 am
Location: WESTERN AUSTRALIA AUSTRALIA

Re: CP Layshaft bushes

Post by ELPS »

Thanks for that. Any idea what clearance they should run? Between the bush and gear that is.
zwarts
Posts: 514
Joined: Mon Jan 01, 1990 12:00 am
Location: LANCASHIRE UK

Re: CP Layshaft bushes

Post by zwarts »

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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