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

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