M21

[maddogmargetts@yahoo.co.u]

The contact breaker assembly on my M21 revolves when i use the kick starter. I am sure i have never seen a contact breaker assembly revolve like this before. I assume this is why i am not getting a spark at the plug because the contacts are not opening. Would this seem a resonable diagnosis? Please could someone who knows help me out? How can I fix this problem.

[MGI]

I experienced this very phenomena once on a Fiat 124 ST, the bearings in the distributor seized and the distributor spun round and round (briefly)instead of the cam thereby winching the plug leads off the plugs bringing me to a standstill, strangely I still remember the incident well, but then I would as it happened at about 07.30 on a wet Sunday morning in Brecon.

[JulianS]

The contact assembly should rotate with the armature. Points are opened by a face cam and tappet. Turn engine over until the points are at maximum opening then check the gap.

[Pete C]

read http://wdbsa.nl/ignition_timing.htm from the WM20 site. It should expalin everything to do with your ignition.

[leon bee]

Pete C: That's the best article I've seen on timing these. Thanks for posting it.

[Pete C]

no credit deserving to me I'm afraid. For excellent information just go to WM20 site and look in the technical section or search and ask questions on the forum.
I have learnt a lot and saved even more thanks to the people on that site

[maddogmargetts@yahoo.co.u]

thank you very much, excellent article. The tappet that transfers the movement from the cam to the contact breaker moveable arm appears to be made of nylon but i wonder if this part is available from anywhere as Draganfly does not seem to have one. They don't do the complete breaker assemblies which is a shame and it appears we have to buy the parts seperately. I will need to look elsewhere. I think this nylon tappet may be worn so that the breaker is not opening.

[Ian C]

May I suggest you contact Tony Cooper.. He deals with all types of magnetos and rebuilds them along with offering exchanges etc.. What he doesn't know about mags isn't worth knowing!! His phone number is :- 0121 559 2405.  HTH

[berniej]

I'll have a rummage in my box of mag bits, I might have a spare.
You're welcome to it if I do. They can wear if not lubricated with a dab of grease on the cam plate occasionally.

Cheers,
Bernie

[berniej]

Found a spare points assembly including tappet.
Will need cleaning up but hopefully of some use.
If you'd like it P.M. me your contact details.

Cheers,
Bernie

[maddogmargetts@yahoo.co.u]

Hi Bernie,
thank you very much and the mag parts will definately come in handy as well. I shall see what the spark looks like after doing the points but I have a sneaking feeling that the spark will indicate a tired mag. It has almost certainly not been touched since 1958 although i think there is a lubricating job to carry out periodically. I am assuming if i can get a fat bluey-white spark after doing the points, the mag must be fine but going on other things on the bike, it's safe to expect a weak reddish spark. The previous owner had replaced exhaust, handlebars, levers, etc so full marks for that but he had also put on a 4ah battery (should be 12ah) and replaced the original regulator with a negative earth one, obviously not noticing that these bikes are postive earth. Of course replacing this for a positive earth got the lights working nicely. From this i expect he has not done the mag/dyno, clutch, points, valves and the other more serious equipment. He also did a rather fine paint job so maybe between us we can get a rather fine bike up and about for another 60 years. Looking at your bike list you appear to have had a fair bit of experience with the M21? I don't know why but i have wanted to own one since my teens - I am now 61 - finally taking possession of this one last march. They are slow, lumbering and thirsty for petrol but there is something majestic about them. In fact if it wasn't for my wife, I'd happily marry one!

[berniej]

Bits posted today.

Yes, a broken down capacitor and/or a break in the fine coil wire are common causes of weak or no spark in the old mags.

I had one that sparked healthily with the plug out but not under compression - took me a while to realise that and it turned out to be a break in the wiring which I guess arced across with the plug out but not when trying to start the bike.

Remember also that the timing affects the spark on magnetos - if it's too far out the spark can weaken or fail.

Cheers,
Bernie