A10 layshaft bushes

[jhg1958]

Can you get oversized bushes for the layshaft?  The bushes are badly scored as is the layshaft. The layshaft is loose in the bearing but it  hard to say of that is normal or important. 

[RDfella]

As far as I'm aware nos layshafts don't exist. I ground down mine until it was clean and then turned up an undersize bronze bush to suit. Easy to do on a lathe but you'll need a proper cylindrical grinder for the shaft.

[JulianS]

The layshaft small bush and journal are often scored.

NOS swinging arm type layshaft on ebay at the moment;

https://www.ebay.co.uk/itm/BSA-A7-A10-B31-B33-Gearbox-Layshaft-f-Swing-Arm-Mod-42-3019/163941607486?hash=item262bae683e:g:84AAAOSw29ZdyteN

Plunger layshaft is different.

[jhg1958]

Thanks for this it is a good spot.  At £130 plus £40 for the bushes I think I will see about getting my layshaft reground. This BSA is proving expensive but I suppose I should not be surprised.

[Swarfcut]

The Layshafts are certainly different, but identical as regards length, the shaft diameters and splines. The essential difference is in the position of the circlip locating groove for the pressed on pinion. The pinions of plunger and S/A boxes are different, having the circlip location machined to match the appropriate layshaft. As long as the layshaft matches the pinion type, they should interchange, but then the rest of the gear pairs may have to be selected to match, as over the years the gear engagement dogs vary in shape slightly...."pointed versus flat"  Worth a try, you might be lucky with what you have.

Worth asking your local crank grinder to put a shine on the damaged layshaft.

Swarfy.

[KiwiGF]

Can you get oversized bushes for the layshaft?  The bushes are badly scored as is the layshaft. The layshaft is loose in the bearing but it  hard to say of that is normal or important.

Short answer yes, there are suppliers who sell them, this relevant ? https://www.a7a10.net/forum/index.php?topic=6053.0

[chaterlea25]

Hi All,
The shafts are not that hard and can be turned readily with carbide insert tooling
The most important thing is to dial in the unworn part of the shaft to absolute zero runout
Forget doing this on a lightweight mini lathe 

John

[Rocket Racer]

As far as I'm aware nos layshafts don't exist. I ground down mine until it was clean and then turned up an undersize bronze bush to suit. Easy to do on a lathe but you'll need a proper cylindrical grinder for the shaft.

every layshaft I've ever seen is worn, so I get my engineer to clean up the shaft and make bespoke bushes.

[Jules]

has anybody tried (successfully) to have the layshaft bearing surface spray welded and reground to size ilo oversize bush?

[trevinoz]

I have had them hard chromed and ground to size.

[Jules]

that's a much better approach Trev, good prompt, I'll see whats available locally, cheers

[Jules]

I just had a closer look at my layshaft and am a bit confused by the wear pattern. Take a look at the photos please, the end (single) gear is very loose on the end of the shaft because the shaft appears well worn, yet its so specific in the wear pattern that it looks like the shaft is "stepped". Questions it raises for help please:
1. does the end gear ever run on the stepped up part of the shaft and if it does then why is the end sooooo worn? the diameters are 0.747 and 0.738, substantially different and so precisely stepped, why??
2. if the gear needs to run along the whole distance then I'll need to either machine it down to same diameter, maybe 0.73, then make a new bush for the gear, this would seem to be the most cost effective solution vs hard chroming and machining back to standard with a standard bush, is there any reason not to do this eg case hardening of the shaft etc??
appreciate thoughts, thanks

[Swarfcut]

Jules. No mystery, its a classic example of layshaft wear. With the layshaft 3rd and 2nd gears assembled onto the layshaft, a hardened steel washer goes on, (internal champher facing clutch side) next to the splined shoulder, followed by the big bushed first gear. You should find the wear shoulder is now level with the front face of this gear. This gear does not move along the shaft. It runs between the hardened washer and the top hat face of the layshaft bush. The thickness of the washer controls layshaft endfloat. The wear has taken place where the layshaft bush in the inner cover supports the shaft.

 Swarfy.

[Jules]

thanks Swarfy, so I think what you are saying then, in reality, is that the rest of the shaft is actually "unused", so its effectively still at the original size unworn?? is that right....if that's the case, then I could just replace the bush in the big (1st?) gear to match the worn end of the shaft and leave the shaft as is (assuming the wear is reasonably even all round), is that a real possibility?? cheers

[Swarfcut]

Jules, the shaft in new, unworn condition is a close as a gnat's knacker to 3/4". BSA Service sheet 702 gives the finished reamed ID of the layshaft bush as 0.7495/0.7505"  This dimension is the same for the bush in your first gear. By chance I have a used layshaft to hand, and the plain part of this measures 0.748", slightly less worn than your largest dimension.

 The clincher is the other end of the layshaft, which gets most of the abuse. Very bad means replacement or custom grinding as outlined above and a custom bush to fit. If this end is OK, replacing the bush on the first gear, plus a custom undersize layshaft bush, size finished to produce a good running clearance with the most worn part of your shaft should fix things. Really depends on the wear pattern and how close to perfection you want to be. You have at least 10 thou of wear.

 New standard bushes are always slightly undersize when fitted, so  you may get away with just fitting one and not having to ream to size.

 Anyone know how much smaller than nominal size these bushes usually are?


  The reason for a softer material "wearing" a harder one is  cited as abrasive particles becoming embedded in the soft bush and then proceeding to machine away the shaft.

 Swarfy.