Hi folks!

I need to know the distance between the center of the mag shaft to it's base.
I think the maggy's base of my m20 is bent or has come distorted somehow. I want to know the right meassure (from a NOS mag body would be even better) befor I start filing and making a spacer.

Many thanks in advance and regards,
Matías.

email (option): mbilamdjian@yahoo.com.ar

Hi Matias,have just measured a fairly good mag base for you,not new but still has the machining marks,only measured with a rule
its 1 3/4".
BSA used shims under the mag base to give a bit of running clearance,i think these are 0.005" thick.is it the mag base that has distorted,or the mag platform on the engine ?
i have a couple of crankcases that have worn,but its mainly the slots that will require attention
hope this helps cheers rick

email (option): richardholt@rocketmail.com

It pains me to say it but I believe that British magnetos came on the scene to replace the no-longer available Bosch instruments during the First World War which means that a lot of the dimensions are metric.

If I'm reading 'Radco' correctly then the height to spindle centre is 45mm which is indeed very close to 1 3/4".

Machines for overseas markets were very often fitted with Bosch mags during the 1930s and they are directly interchangeable

You can't take much off the mag base without breaking through into the clutch housing. Also, I have found they usually wear unevenly with more wear being present at the points end generally. (likewise with the crankcase mag platform).
If the mag platform is worn it can be machined off to make it flat again. If the mag base is good machine off the equivalent of one material gauge from the mag platform, then it is an easy job to make up a spacer plate from standard material to restore everything to the original dimensions.(20 gauge or 18 gauge is usually enough).
If the mag base is worn, rather than remove material from the base, which is a limited option anyway as mentioned, I usually make circular shims which fit over the 5/16" pegs in the base but have an outside diameter of about 13/16". This allows you to shim each 'corner' of the mag individually, adjusting each shim stack to account for the uneveness of the base and to achieve the correct drive gear mesh.
A little silicone sealant will keep the shims in place as you fit and remove the mag to get it right....Ian

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

Rick, Rik and Ian,
Thanks a lot for the help.
Really almost everything is distorted. Mag base, crank platform, dowel's slots, and the worst part, the mag oil seal holder.
About a year ago I did something quite similar to what Ian advised. I made four new dowel pins, with a smaller diameter exposed part. Then I trim with a file four one off brass made "shoes" that will take the deformed dowel slots slack, and used some steel shims to get the maggy level, and repaired the seal holder with the help of Noam Pollak's drawings.
That was made on a friend's bike. Guess it's time to do it on my own.

Well, thanks again guys!

Cheers!
Matías.

email (option): mbilamdjian@yahoo.com.ar