Andrew here from Priory Magnetos! Obviously I would like a rebuilt magneto to give years of trouble-free riding but, given the way our bikes are used and stored, the magneto has a harder life than it would if it were used on a regular basis. There are all sorts of issues to do with condensation etc. I rebuild about 100 magnetos per year and I guess I get, literally, one or two back where something has gone wrong. Magnetos which have been in regular use for a reasonable period of time, say two years or more, and have been functioning well sometimes seem to lose their 'joie de vivre' and don't perform as well as they used to. Some owners overlook the fact that a magneto needs maintenance; I make this point generally and not specific to this thread though it may be a factor. Everybody in the Cheshire Branch of the BSAOC has one of my rebuilt magnetos on their bike, so I feel a massive weight of responsibility every time we go out on a ride and, once in a blue moon, something goes wrong, even on my own bike! Back in the day nearly every village would have a person who knew his way round a magneto and come out and fix a minor problem. This is no longer the case, and if my mates were completely honest they would say that they don't touch their magnetos from one year to the next because I'm on the end of the phone, can lend them a mag or fix theirs or whatever! The point I'm making is that a magneto needs to be properly serviced, ideally every riding season. This does not mean that it needs to be sent to the 'Magwizzard' but it does mean that an interested owner will learn how to do it himself. Everything that can be checked needs to be checked. Here's a list which is not exhaustive.... Spark plugs - clean, gapped, renewed if it helps; Ht leads and plug caps - zero resistance from cap to split washer in pickup, clean and dry and undamaged; Pickups- clean, undamaged, decent quality, minimal resistance though the brush to the split washer contact, good quality brushes, springs checked so the brush contacts the slip ring, brushes free in their slots; slip ring - clean and resistance through to body of about 5k ohms assuming earth brush is OK; earth brush- free in pod and spring functioning correctly, zero resistance through brush and body; earth track on armature- clean, dry, free from any oil or grease residue; armature- no endfloat or vertical play; points- clean, dry, gapped, continuity and resistance checked when open and closed..... and there's more!! The majority of problems I have with magnetos I have built and have been running for several years is dirty earth tracks and earth brushes - worth checking a few times each year. Problems with the windings and/or capacitor are virtually non-existent. The list I have provided looks like a hell of a lot of work but it really isn't. You don't have to take the magneto off the bike and it can all be achieved in less than an hour unless you encounter a problem.
