What on earth is wrong with this magneto?

I'm no longer confused. I'm tired and I was reading the wrong scale on the megger. The results of the insulation tests should have been:

HT coil: 120 kilohms Condensor: 100 kilohms

I'm sure the figure for the HT coil shouldn't be that low.

So I have a couple of questions for those who have been in this situation before.

Firstly, can I expect the HT coil to recover to the extent that it produces a good spark, if I get it nicely warm and then give it a new coat of insulating varnish (it is not open circuit)? The coil is dated

1977, if that helps. Or do I need a new coil?

Secondly, does the condensor need replacing?

I'm surprised that this has happened, given how well sealed the Series "A" magneto body appears to be.

Best wishes,

Chris

Wipac = Wico-Pacey

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk

What about the strength of magnetism in the magnet?

I would be inclined to open it up and leave it on the top of a radiator for a week to dry out. Might help and no harm can be done.

I certainly concur with the "warm it gently" advice & two weeks should do it. That done - and if it checks out electrically, of course - I'd warm it in the oven until it is just a bit too hot to handle comfortably. Whilst it's cooking, make up some hard set Araldite & paint this on to the hot winding as it cools. Eventually it will stop soaking in - it goes runny when hot - & will improve the insulating properties whilst holding the wire better than damp (or hot!) Shellac.

This treatment also fixes porous castings, I did any number of Mk II Amal Concentrics from the last days of the Meriden Triumph Collective's Bonevilles. If it was quiet, I'd pull off carbs from stock Bonnies & do them before they were ever started. If you ever bought a Triumph from Greys in Bristol in the 70's, I'd PDI'd it.

Regards,

Kim Siddorn

I did a bit of reading in my books on electrical engineering. Following some advice in a book published by Brook Motors, I've put the magneto coil in the oven. It's sitting there now at about 105 deg. C (as recommended in the book) and looks perfectly happy. I'm going to leave it there for a day or two and hope that does the trick.

Just out of interest, has anyone here found that drying the magneto coil has proved a lasting solution to a weak spark problem? I really want this magneto to be reliable as I want to use the lawnmower regularly.

I'm cautious about applying Araldite to a magneto coil, as I know nothing about the glue's insulating properties. I have a container of insulating varnish, but I'm not sure if it'll be compatible with the original varnish. It looks very different.

I'm rather surprised that this has happened to a magneto like the Series "A". The magneto looks well sealed. The only openings I can find are the oil tube and a miniscule hole in the centre of the contact breaker cover. I'm going to see if I can get replacement gaskets and possibly another contact breaker cover (or I might fill the hole with solder) to see if I can keep the damp out in future.

This lawnmower has a pre-monobloc Amal concentric carburettor which fits onto a 1" diameter spigot. Amal part no. 47/022/S/LAC. Amal can't help me with parts. Apparently it hasn't been made in a long time. Fortunately the carburettor looks pretty good. It's brass and doesn't look porous. I suspect it pre-dates the concentric carburettors you're talking about.

Best wishes,

Chris

I've no scientific way of measuring, but the magnet seems as strong as one I have in another Series "A" magneto which gives a good spark.

Chris

Is this Camping Stove Man?

Chris

Sorry, I should have made it more clear what I meant. You referred to a Martin Percy in your message. Camping Stove Man signs his messages "Martin P" so I thought perhaps they're the same person?

Chris

As to the insulating properties of hard set Araldite, I have used it successfully in the past to repair HT slip rings when some fool has tried to remove the magneto armature without taking out the overload screws from the body! In my experience, it is certainly proof against the (say) 18kv found in the kind of magnetos we use.

The MkII Concentrics are square bodied & fitted to British 1970's motorcycles. Early ones suffered from porosity & air leeched through the casting causing the engine to run weak on tickover. Untreated ones have been known to literally crumble away after a few years! Yours will be a lot older & may be made of brass.

Regards,

Kim Siddorn

Do you know roughly what Martin Percy charges for rewinding a magneto coil (this magneto is a Series "A")?

Not sure if I'll need it doing. The coil is still in the oven tonight.

Best wishes,

Chris

I think I'll try a bottle of Electrolube "MR8008" insulating varnish I have, and hope it is compatible with the original varnish.

The original varnish has darkened somewhat in the oven. Hope this isn't a problem...

I'm pretty sure it's brass, but it could be bronze. I'll take some pictures once I've got the lawnmower running.

Best wishes,

Chris

I had a similar problem with a 'new' wipac a series - It turned out that the connection from coil to cap was at fault -Just curve both cotacts so you can feel a slight resistance when you fit the cap . The condensor - I proved mine by fitting a spare lucas one from a mini - it just fits ! Hope this is of help -If not a guy I know in hull used to repair them for a living - and is cheap! Julian

I took the coil out of the oven today and did another insulation test. It's lower than before - 80 kilohms - so I don't think the coil's going to recover.

The coil covering has darkened noticeably in the oven. Possibly I got it too hot, although I was very careful and used two thermometers to keep the temperature at 105 deg. C, the temperature recommended in my book. It was also a similar temperature to that which Kim recommended: just a bit too hot to touch.

But if anyone else reads this and thinks of drying an old magneto coil in the oven, I would recommend a slightly lower temperature, perhaps 70 or 80 deg. C. I suspect 105 deg. C may be a little too hot for the old shellac (or whatever it is) used to insulate these magneto coils.

Julian: I'm going to look for a complete magneto at a good price, to maximise my store of spare parts. But if I can't find one, I may get back you for the details of the chap in Hull.

Best wishes,

Chris

I decided to take a chance on a used magneto, and scored one on eBay:

The case looks unusual. I think it might be an all-metal case. If so and the magneto works without problems, I think I'll just use it without trying to rebuild the other magneto. It looks interesting.

Best wishes,

Chris