Dave. Looks to have some life, so before you condemn the original magneto, a strip down and a good clean could be all it needs. To use Zen on it, it doesn't work properly now, so if you are unsuccessful, nothing has been lost. Stuck or well worn brushes, dirty slip ring and dirty, sticking points are the first checks. Earth brush adjacent to the nameplate is often worn down, and is an easy but often overlooked first check. The bearings are insulated from the body and without this brush there is no easy earth return to the armature.
BSA Service Sheet 801 (Find in the Forum Literature Section) shows how to do basic maintenance, dismantle and do electrical checks.
To remove the armature, first remove that earth brush and the spark gap safety screws. These otherwise foul on the armature and slip ring as the armature is removed. A clean out of the body (expect to find carbon, dirt, oil) and fresh grease on the bearings should get something good enough to start the bike. Failing condensers will often work cold, then give up as they warm up. Replace any spacer shims as found to retain original bearing running clearance, the unit uses cup and cone bearings which will simply pull apart.
Priory Magnetos and Brightspark Magnetos have very useful websites and I would recommend time spent here. Brightspark have a library of old Lucas Part Lists, and you can identify the correct Lucas Magneto Model Variant for your bike. They also market an effective
well proven and cost effective replacement for a failed condenser.
Manual and auto maggys share the same basic body casting and electrical internals. The difference is in the camhousing and the attachment of it to the body...just a difference in the number of tapped holes.
If searching for a replacement magneto, "Proper BSA Ones" have a flat machined on the base to clear the cylinder barrel flange. Without the flat, other bodies fit, but it's a bit of a squeeze.
Swarfy.
