Lucas N1 magneto

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Lucas N1 magneto

Postby AJS_Chris » Mon Mar 18, 2019 9:52 am

Hello all.
My Model 18S starts easily from cold, even if it's been stood for several weeks. Starting when hot is a different matter, it keeps me fit though. Having read various articles it points to the magneto condenser but I wanted to investigate further.

I removed the armature and there are a pair of light grey condensers, I've not seen this configuration before, has anyone else? The armature winding looks newish, as though it has been reconditioned. I've had the bike a couple of years but don't know the history of the magneto.

Anyway, I cleaned it all up and put it back together. I then popped it in the lathe, supporting the body, and span it up. I tried to measure the speed of the engine with a tacho when kicking it over, not easy, but I reckon it was about 180rpm so I set the lathe speed to minimum, 250rpm. I popped a screw into the plug cap and positioned it about 3mm away from the magneto body, set up like this I could get a good spark. With the lathe running I heated the body of the magneto with a heat gun, after a while the spark became intermittent and finally stopped altogether. Leaving the lathe running without heat the sparks returned after a few of minutes.

So, I believe I've proven the starting difficulty when hot is down to magneto. Am I talking complete rubbish?

I've looked at the condensectomy but with my magneto having a pair of condensers with what looks like araldite holding the condensers and wires in place it looks too tricky to try to cut the wires without striping the armature and I don't a suitable bearing puller to do that anyway.

I guess the next step is to get the magneto tested by someone who actually knows what they are going. Can anyone recommend someone, I'm in the south-west, near Bath.

Thank you in advance,
Chris.

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Re: Lucas N1 magneto

Postby SPRIDDLER » Mon Mar 18, 2019 10:41 am

I believe the club spares have recon exchange mags: http://www.amoc-parts.com/store/comersu ... tegory=122
and I seem to recall 'ajscomboman' recently suggesting on here that's there's a guy in Salisbury...... :?
Also:
Have a look at the 'Recommendations' section here:
viewtopic.php?f=10&t=17644

It's the business of long time club member 'Groily' so you can be certain you'll get good advice and a fine job at sensible cost.

http://brightsparkmagnetos.com/index.htm
I poke badgers with spoons.

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Location: Wiltshire, UK

Re: Lucas N1 magneto

Postby Andy E » Mon Mar 18, 2019 2:02 pm

D H Day in Wroughton near Swindon sorted out the N1 from my 18s. Like others in the trade they seemed to be busy and it was 4 or 5 weeks before I got my magneto back.

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Re: Lucas N1 magneto

Postby Groily » Mon Mar 18, 2019 5:32 pm

Just to say - and NOT looking for work I promise, there is far too much of it about! - but a decent N1 ought to be making continuous sparks, no misses, at a rate of about 2 per second, by 130rpm anyway, fully advanced, using a seriously quite big 5.5mm test gap. Really good ones will do that at 110rpm. Hot (50°C and well soaked at that temp), they should do the same around 150rpm. Retarded, add a handful of revs.
The symptoms suggest the condenser(s) is/are at fault from what you say. Little grey ones, clear plastic ones (or twos-es) with a yellowish hue, plain yellow ones, red ones, you name it, they're around and about.
On an N1, you pretty well HAVE to get the armature apart to deal with it, although a few courageous people have managed to cut out the condenser there and fit one on the cb without ending up with a short on the low tension side. But it's quite fiddly, and where resin and epoxy are around, risky sometimes for the reasons given. Usually, if the bearing race can be pulled and the armature split, it's not so hard to pick the glue off and salvage the wires, but sometimes . . . it's misery.
The other most likely thing to be causing failure when it gets hot is the slipring, if it looks like an old one. Sometimes the pick-up leaks too. The winding is probably OK - guessing, but most recently rewound jobs are good.

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Location: Wiltshire

Re: Lucas N1 magneto

Postby AJS_Chris » Mon Mar 18, 2019 6:06 pm

Thank you for the replies.

Groily - appreciate you're not looking for work but I'm not looking for a quick turnaround, would you be able to fettle it for me please?

Regards,
Chris.

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Joined: Thu Jul 04, 2002 12:00 am
Location: NORMANDIE FRANCE

Re: Lucas N1 magneto

Postby Groily » Tue Mar 19, 2019 6:26 am

Hi Chris,
Sent you a PM . . .
Cheers, Bill

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