Layshaft bushes for 1st and 2nd gear 1951 CP

[walter.murphy]

Gents

I stripped the CP gearbox on my 1951 NH and besides requiring welding and reconstruction on the outer case, I thought the innards would be okay as it changed gears before I stripped it. Besides the incorrect output sleeve bushes being too sloppy I noticed the 1st and 2nd gears had what appeared to be brass bushes inside worn to the consistency of tin foil.

The difference in the inside diameter of the gear .861" and the outside of the shaft are .781" which gives a bushing with a wall thickness of .040".

The main thrust of my question is that I noticed the inside diameter of the gears has helical oil-ways and holes, and the shaft is just a plain ground surface.

Does this indicate that the bushing (which I would make from bronze) needs to be pressed onto the shaft and the gear turns on the outer diameter of this pressed on bush?

Or Have I interpreted this all wrong as the exploded diagram does not show these bushes?

Best Regards

Walter

[greg.geonetta]

Yes, the layshaft bushes should be a press fit on the shaft, and the gears spin on the bushes.

After long use, the bushes loosen up, and might come free. this was the case when I disassembled the Burman box out of my '51 SQ4.

[walter.murphy]

Thanks Greg

These ones are worn beyond recognition and were spinning in the gears themselves.

Cheers

Walter

[johnwalsh]

Some boxes, ie.AMC, have a floating bush. Certainly on 3rd gear from memory. The bush is free to rotate on gear and shaft.

[john.whiting]

Both Norton early style and AMC gearboxes have some bushes which are a thumb press fit.The Burman layshaft bearings in question are a tight fit on the layshaft.They are also made of sintered material,and making bushes of solid bronze in a box where lubrication may fail due to lack of oil,or the use of grease,risks a damaging seizure.I always use sintered material in a bike gearbox that I will not be operating myself.How do you know when your gearbox has run out of oil?It stops leaking out.Regards John.

[Pete.Silson]

I have revisited this old thread because I have the same problem with my 1949 CP box. The 1st/2nd gear layshaft bushes are knackered and are is not listed as a seperate spare part by Ariel. My layshaft however is in reasonable nick and has a very good speedometer drive on it so I don't really want to scrap it.

Does anybody know a source these bushes or do they have to be made to order? If I need bespoke bushes - any suggestions for somewhere that might produce them?

Pete

[john.whiting]

gearbox repairs dont come much simpler.........just press bushes onto the layshaft ,and turn them to fit the gears,........ using the centres in the shaft,what could be easier ?.......I notice in the army spec for the Matchless G3L,there is a "hard bronze" specified.......but check that yourself ,its a while since I waded thru the hundred odd pages of the spec......The prewar boxes dont seem to have used any bushes ,just run steel to steel.

[nevhunter]

They only spin freely on the bush without load until they are dogged into engagement, then they don't move on the bush at all. If the box has clean oil in it they should almost last forever. If they have play the mesh of the gears is not correct (noise) and the dogs wear more than they should which makes then want to fall out of gear eventually. Nev.

[john.whiting]

At a casual glance,it seems the layshaft bushes might be a smaller diameter than the splines adjacent,which would make them difficult to install......possibly why they are considered part of the layshaft......but I dont know...........I looked in my gearbox bits,and none of the bushes are tight in the gears ,but not badly worn either...... ,the prewar boxes seem to be steel to steel,no bushes.............But getting back to what I mentioned 2 years ago........I never use anything but sintered bronze in someone elses box.......if you run out of lube with solid bronze ,a monumental seizure is guaranteed.

[Pete.Silson]

John, Nev - Thanks for the replies.

This CP box was on a 500 single that looks to have been used with a sidecar so probably had quite a hard life. When I dismantled the box it was virtually dry and the grease that was in there was way too thick to get anywhere near the gear cluster. Everything turned freely however the kickstart-side ball bearing was totally shot with 60+ thou of sideways movement on the mainshaft. I suspect this may also have loaded the layshaft bearings which were also very worn. The 1st gear bush was so loose that it dropped off layshaft when disassembled.

The gears and selectors themselves appear to be OK and I am hoping that replacing all the bushes and the ball-bearing will tighten up everything sufficiently to get some more miles out the box.

When I get my lathe up and running again, I will probably make the layshaft bushes myself. Is there any particular grade/type of sintered bronze I should be using? The current bushes look to me like some sort of brass rather than bronze.

Pete