Cp box puzzle...

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Druncle
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Joined: Tue Nov 08, 2016 1:51 pm
Location: CO.DURHAM UK

Cp box puzzle...

Post by Druncle »

Evening all...
Having fun with a CP gearbox at present and wondered if anyone might be able to help.
On re-assembling the box ( after remedying worn layshaft bushes), several times😕, i am confident everything is going back in place nicely. With inner cover off, gears seem to select ok, so on go the covers. Once all is assembled, when selecting gears, the box seems to lock up..
The mainshaft will turn by the sprocket, but only by a degree or so. All shafts seem straight, doesnt seem too much play anywhere... anyone been here/ done that/ and fixed it?
Cheers John.
g80csp11
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Re: Cp box puzzle...

Post by g80csp11 »

take your pick
layshaft bushes are not fully home and pinches on shaft or more likely you have not used gasket between inner cover and case
Druncle
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Joined: Tue Nov 08, 2016 1:51 pm
Location: CO.DURHAM UK

Re: Cp box puzzle...

Post by Druncle »

Thanks g80...
The layshaft bushes in the gbox casing have been untouched... the bushes referred to sit on the shaft. A new shaft was located and installed. (Old shaft was tried yesterday with same results). Gasket used. Layshaft can be seen turning, Dots on selector shaft timed correctly ...😕.
Chris Berry
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Re: Cp box puzzle...

Post by Chris Berry »

On my gearbox I had a similar problem. I'm not sure if this is the same problem as yours but on mine I found that the spacer/bushing that the kick gear turns in was a little long. When I tightened the nut it caused the whole main shaft to bind up. After I linished the bushing it all worked OK
Druncle
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Joined: Tue Nov 08, 2016 1:51 pm
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Re: Cp box puzzle...

Post by Druncle »

Thanks Chris.. that did occur to me, however there is still some shaft rotation, albeit only over a few degrees. Have weekend off so will double check that.
Otherwise am wondering if its a selector issue, in that too many ratios are trying to engage at once, and locking up, if that makes sense. I haven't started hitting things with hammers yet!
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ajscomboman
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Re: Cp box puzzle...

Post by ajscomboman »

Had a similar issue with B52 box in that I could rotate the shafts but not get any gears. Turned out that the box had been converted by an engineer to needle rollers instead of bushes. It was a superb job which involved grinding the shafts to the correct diameter but he'd made all the tolerances so fine that as soon as the covers were on it all bound up tight. I stripped rebuilt it using old replacement shafts and bushes with more clearance (some may say sloppy) but it's now the sweetest changing Burman box I have out of the 4.
Druncle
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Joined: Tue Nov 08, 2016 1:51 pm
Location: CO.DURHAM UK

Re: Cp box puzzle...

Post by Druncle »

Aha!!
Well maybe..
I put a bigger sprocket on the gearbox, with a new m
S. oil seal.
There is side to side play on the drive sprocket /shaft. When the shaft is pulled away from the box (iyswim), the gears seem to drop in (engage) ok. Do not recall there being any spacer here, however the drawings suggest otherwise. Will follow this line of thought and see where it takes me 😁
Druncle
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Joined: Tue Nov 08, 2016 1:51 pm
Location: CO.DURHAM UK

Re: Cp box puzzle...

Post by Druncle »

Maybe not !
Druncle
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Joined: Tue Nov 08, 2016 1:51 pm
Location: CO.DURHAM UK

Re: Cp box puzzle...

Post by Druncle »

Ok...with gearbox reassembled with old layshaft, now the box seems to work ok. Guess the internal wobbliness suits it. Mind, after removing/ replacing the sprocket, sensibly omitted the sprocket nut and washer, so will have to take to bits again 😣. And itll no doubt stop working again haha! So if it has been sorted, i'm not sure what ive learned here, other than how to assemble cp boxes in my sleep 😁
Thanks for the advice folks, will crack on with the rest of the beast.
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ajscomboman
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Re: Cp box puzzle...

Post by ajscomboman »

It's been my experience that with a Burman box they work far better when there is plenty of play bushes, far more so than with the AMC box.
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