Magneto - repair

- by Richard Rowe

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While trying to diagnose the reason for erratic behaviour of the magneto in my Chummy I found that the fibre gearwheel in the distributor had lost rather a lot of teeth.

This was a progressive failure as one tooth must have broken off and stuck in the smaller steel gear on the armature which then damaged the opposite teeth as the larger gear rotated.

image 1

Lost teeth

Not having a new gear or the ability to cut a new one (I did inherit a small lathe but not the skill to go with it) I decided to perform a dental repair by moulding new teeth in place.

image 2

Making mould from good teeth

Rather than use the disgusting tasting dental impression material I used silicone sealant as it was in stock. This was held against the remaining good teeth on the gearwheel.

image 3

Silicone mould

After applying JB weld epoxy to the gappy teeth the silicone mould was used to form the new teeth. This was repeated at all 4 gaps around the gear.

The excess was trimmed off and the new teeth tidied with a fine file.

image 4

Moulding new teeth

The mag was bench tested at 3,000 rpm and replaced in the car.
All running well at the moment, will have to see how it lasts so now always carrying a towrope and AA membership card.

image 5

New teeth before tidying

This solved my problem but is it a recognized standard technique?


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