EL014 ELECTRICAL

What is the procedure for setting the ignition timing for a 1952 alloy engine MAC fitted with a BTH magneto (Understand it is different to the lucas set up that is detailed in the books?) - Jon Hurst, 7/11/2002

The procedure for timing your ignition depends not on whether you have a BTH or a Lucas magneto but whether you have automatic advance and retard or a manually controlled A&R.
Either magneto could have either type of A&R, though it is true that Lucas magnetos had an automatic control more often than BTH.
Even so, the main difference is that for a manual control you just make sure the handlebar lever is at full advance, whereas with an automatic unit you have to remove the timing cover and wedge the unit at full advance (i.e. the springs extended and the bob-weights at their maximum travel). The rest of the procedure is as in the book and the same for both, except that if you need to adjust the timing you have to remove the magneto drive gear and on a manual magneto this is by using a small puller working on the two threaded holes in the gear wheel, whereas the automatic timing device has a self-extracting holding bolt that you just unscrew and it pulls the ATD off the taper. - TW 7/11/2002