DIY Magneto Rebuild - How Difficult???

[brackenfel]

Dear All,
First of all this isn't on the A10, that's fine (apart from the "clonk" from the front forks on rebound....)..

Took the B33 for it's MOT in my ownership, rode there, back on a recovery trailer! The bike started fine (as usual), ticked over like a (slow) watch as usual & rode to the MOT well. It was the first long trip it had done for 10 years though..

Passed fine & then would not start, period.. The MOT place is great but deals with modern stuff mainly so I had to be recovered.
 
No spark of any kind.. Have substituted plug, HT lead, pickup etc from another old (also non-functioning) mag off the NH350..
Cleaned slip ring (it was already fine) and at this stage actually got a "belt" though the finger I was using to clean the ring!!! (I know, I thought it was very dead!!)
Still no spark at the plug..

So, I know there's a very good bloke who does mags & dynamos near Salisbury, but... It's not the cost, just the thought of 2 return journeys or risking things in the Royal Mail which does not appeal..

How difficult are these things to get apart? Once apart is there anything I can look at that may help??  Something failed suddenly that didn't affect the bike when it was running (I had to use the decompressorto stop it before the MOT), ie turned over fast enough it produced sparks but not when turned slowly..

All thoughts and experiences appreciated..

Thanks,
Adrian

[MG]

Hi Adrian!

You can check the points, earth brush and slip ring rather easily. Taking the armature out and testing it according to the Lucas service sheet (misused as a battery coil) is not too hard either. If you follow the procedure for dismantling and testing in the service sheet you can't go wrong.

But: if you have to get to the condenser, the armature has to come apart, which requires either a special extractor or some sort of home-made contraption to withdraw the bearing race on the slip ring side.
If the armature has failed and needs to be rewound, you are soon at the end of home workshop possibilities. I have successfully rewound my own armatures using a coil winding machine, but it is an awful lot of work, winding hair-thin wire with insulation material over each layer, and vacuum impregnating the whole thing later. I wouldn't wanna do it for a living, took me half a day for each. So if you got someone who does a decent job, pay the man! Unless you like a challenge and want to give it a try of course.

[Tukig]

Hello Adrian,

Thought about a DIY mag rebuild myself but was stumped by the bearing removal. I cautiously tried the copper wire in the bearing track and hammer but chickened out. Replacement mags are expensive, second hand and probably need a rebuild anyway. I sent mine off to APL Magnetos and was very happy with the cost and turn round time. 2 year guarantee as well. There some good diagrams for bearing removal tools on-line in this and other forums but they were out off the question with my limited selection of workshop tools and as has been said there is always the armature and condenser to deal with.

Just a comment about Royal Mail. I rely heavily on mail order up here in the north east of Scotland and Royal mail has proved to be the most reliable service with nothing lost and prompt delivery unlike some courier companies. I would now use no one else.

In conclusion: send it away and then enjoy a guaranteed reliable mag.

Cheers

Gary

[bsa-bill]

Just a comment about Royal Mail. I rely heavily on mail order up here in the north east of Scotland and Royal mail has proved to be the most reliable service with nothing lost and prompt delivery unlike some courier companies. I would now use no one else.

Sorry bit off topic I know but worth giving the much maligned Postie a thumbs up, all my bike gear comes through to the post and as we live out in the sticks and often out as are neighbour the postie leaves it in the bike shed siqning for me if needed.

[brackenfel]

Many thanks markus, Gary & Bill,

Rather as I imagined, you can have a quick look & hope you're lucky or after that it's a job for those that have done it before (and have the equipment!!)
Thanks for confirming that though...

Our local posties are brilliant also, I wasn't sure if that was universal as stuff does go missing across the country sometimes! There's also the question of who the person uses to send it back.. Certainly other companies are to be totally avoided (one that Links very large towns for example!!). I guess I could send it heavily insured for say £300 and then go & collect it myself (persuade the wife it's a nice day out!!)

I do like a challenge so I'll have a brief look inside & then contact the expert

Cheers,
Adrian

[MG]

If it is a rotating magnet version like the Lucas SR series it all is a fair bit easier. If it is a rotating coil mag (N1, K1F, etc.) don't forget the safety gap screw, or you'll ruin the slip ring!

[wilko]

Take off the points and plate,and have a close inspection. There might be an insulation washer broken or something similar. It's odd that it went so far and not start again after a rest like most of them breaking down?Old ones do need a Nanny nap!

[brackenfel]

Thanks Wilko,
I'll take a look.. I'll also have a look at the parts list but no washer has emerged under the plate.. Am not sure if you can get the washers that fit in the points, I guess the restorers will have them but keep them to themselves!
It's a Mo1L mag if that's any help ..

I think that I'm going to have to call APL at Shaftesbury ( he has a good reputation & is relatively near). I've probably got two to do as the very similar one from the Ariel NH350 doesn't spark either, wonder if I can get a "volume discount" !!!!

Cheers,
Adrian