Along with gearbox & clutch build I am re-installing the mag on my bike as over the years the base has worn , mag missing some locating pins and running loose at times the cause

Result is worn base & an oval casing where the seal is located

To get through the riding season I will replace the pins & add shims as I believe the mag is too low and little or no backlash is present - this might explain a split pinion due to excessive loading

Could those more experienced amongst us let me know how many shims were commonly found. I know each motor was different due to tolerances etc, but was there a std fit, 1 shim or 2 and how was this judged at the BSA factory, guess work or a specific check procedure

Hopefully you can help

Many thanks

Job

email (option): Jonnyob1@googlemail.com

Hi Douglas

I have shims, got them from russels

I can guess & use paper through the gears or try something like Prussian blue to check gear height engagement but there must be a easier way

For sure I have lost 1 pinion gear - split - and I must be loading the armature too, can't be good

Would like to know how the factory decided what & how

Best regards

Job

email (option): Jonnyob1@googlemail.com

Keep adding until you get a tiny bit of freeplay between idler and pinion gear teeth, it's easy.You'll know if it's too tight by a whining noise when running.Of course you must tighten the clamping strap for testing purposes to get a true reading.

There is no specific number of shims as far as I am aware. That would not really be logical anyway as you are making an adjustment with the shims based on varying degrees of wear/ machining tolerance on the mag platform and mag base.
To get an idea of the amount of free play needed check the play between the large idler gear and the inlet cam gear before you start.
Wear on the mag platform is always heaviest at the 'points end' of the mag base I have found.
For this reason I fit circular shims around each pin in the mags base rather than the one piece shim with four holes. This allows you to account for the different degrees of wear across the platform.
I use a little clear silicone to stick the shims in place while the mag is refitted..Ian

email (option): ian@wright52.plus.com

Hi Ian/ Douglas

I suppose with fixed points backlash between the cam and idle gear are fairly much fixed and a good basis for checking

It's clear there is no clearance on mine as last time it was out I noticed the mag moving slightly even though the strap was tight

As to shim availability Ian, do yo make your own and if so, where do you get the shim material

For this exercise, I might just chop the full shims I have and agree with you, points side is where I have noted wear

Best regards

Job

email (option): Jonnyob1@googlemail.com

I bought mine wisely so

Ian's idea of small circular shims sounds a good one however

I might try rs components or farnells for shim material

Job

email (option): Jonnyob1@googlemail.com

Hi John...I think RS have it in sheets...I usually cut up the original brass shims, not that I do it very often....this can easily be done with a pair of sharp scissors..
When working from 'blank' sheet shimstock I usually clamp it between two bits of thin plywood and drill the holes through, trimming the outside to size afterwards with scissors or sharp Gilbow tin snips, depending on thickness..Ian

email (option): ian@wright52.plus.com

Cheaper to cut up the old ones

:-D

Job

email (option): Jonnyob1@googlemail.com