BSA M Inner Gearbox - Wear around speedo drive

[Barrieh]

Hi Guys,

I am sure this a common thread as it seems to be a common problem. The inner case of my BSA M Plunger gearbox is worn around the kickstart quadrant and speedo drive area... Its grinding metal. I have managed to get a new inner case for the gearbox part which is in amazing condition but I am worried about it getting damaged.

Does anyone know what is causing this e.g. which part or parts are worn that are causing this internal damage and how I fix it.

Many thanks for all your help.
P.S. I managed to get plunger columns from Baxter cycles in the USA... last pair and the bike is coming together nicely.

[Rog1]

My M series inner gearbox has cracking in line with the speedo drive, visible behind where the quadrant sits. I assume it was where the drive was replaced using too much force. The kickstart spring looks worn down; ground flat on the side that faces the inner case. It occurs to me that a pattern quadrant might not have quite the right dimensions.

Well done on the plunger front... Er, rear...

[Blackthou]

It can only be an alignment problem, centres not on centre, too much end float or incompatible gears is another i.e. different teeth profile / pitch / diameter.

[Rog1]

Further to my previous post here, I knew I had some photos somewhere, and here they are. Is this the wearing area you mean, Barrieh?

[Barrieh]

Hi

As you can see the quadrant is damaging the case.

We have a few candidates for the reason for the wear.

1. The layshaft / speedo bush that the quadrant sits on.
2. Kickstart bush through outer cover
3. Misalignment
4. Loose kickstart that enables the quadrant to be pushed back


Have seen many inner gearbox's with this damaged area. I have managed to get a nice one but fear it too will be damaged hence the need to have a full and clear understanding.

[idie]

Doesn't a rubber stop fit in the cover?

[Barrieh]

Indeed, interestingly the stopper was missing from mine, but I have bought a couple from Draganfly along with new bushes, bearings etc, for the reassembly.

The only issue I have at the moment is that I need to extract the speedo drive from the old inner cover but the grub screw top is knackered.

The only option is to carefully drill out the old grub screw unless any of you have another solution.

Hamish

[Barrieh]

I think I have worked it out.

The Kickstart Quadrant is kept aligned in the Bush, flush, so long as your kickstart leaver is tight. If the kickstart level is in anyway not tight it allows the kickstart quadrant to rotate in as you press it down. This in turn causes the spring on the Kickstart Quadrant to move against the inner face of the gearbox hitting the area around the speedo drive area.

Solution - Ensure that 1. the Bush that holds the kickstart quadrant is not worn by the kickstart lever.
2. Ensure that the kickstart lever is flush with the face of the bush and cannot allow play.

[Blackthou]

Well done, sounds logical and as I said too much end float has allowed the head of the bush to be worn away and into the casting.

[Rog1]

I would guess that the issue with end float was happening on my bike with the previous owner, who fitted a new quadrant and stopped it. But good grief, it didn't get as bad as your one, Barrieh. I do have a rubber stop, but it's in the outer case. I see you've got the same missing corner as I have, where the stop fits into the inner case.