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Alternative Ignition System for GNs.


27th Apr 2020

Most British built IOE GNs use a single 90 deg V twin anti clock magneto. Finding a spare as a back up is not easy and if it is a Fellows it won't be much good anyway.  Coil conversions are a common alternative but for those who wish to stay with a magneto there is another option. The good thing about a 90 deg V twin is it can be made to operate with a 4 cylinder mag. Basically you select 2 plug leads at 90deg to each other and earth the other 2 leads. 

A camshaft pattern magneto is required (input shaft & rotor arm must rotate at the same speed) for this setup but driven at crankshaft speed. The 1:1 chain drive will need to be changed to 2:1. The magneto I have used is Lucas 4VRA . These are very good rotating magnet magnetos and are readily available at most autojumbles in clock & anticlock form, some incorporate an auto advance mechanism which adds to the size and weight.

This is easily removable but still too big to fit on the mag platform. I have turned the mag through 180deg and mounted it on the front chassis cross member ( a clockwise mag is required ). This ignition arrangement will spark at every TDC not just the compression stroke. Citroen 2CV ignition systems work like this too !  On my GN the ignition advance is fixed at 3.25" as measured on the flywheel circumference. The photo shows the mag installed. The inlet manifold has been removed for clarity.

Peter Still

For any comments please login to the Members Login and go to  GN Magneto overhaul in  Workshop Chatter