What on earth is wrong with this magneto?

Hi folks,
I have a Wipac Series "A" magneto on my Dennis lawnmower. I didn't realise until I got this magneto that the Series "A" had been sold under
the Wipac name.
Anyway, it isn't working properly. The spark is incredibly feeble. It won't cross the plug gap. I can only just see the spark if I hold the end of the HT lead about a tenth of a millimetre away from the magneto body. So the spark is there, but it's pathetic.
The magneto's got an impulse coupling, so it should produce a decent spark at a low speed. It doesn't produce a spark through the plug at all when the engine is turned at a sensible cranking speed.
Overall the magneto looks in good condition. It's been stored in a damp environment for a few years but inside it looks great. Like new in fact.
I cleaned the breaker contacts. They look good. A miniscule amount of pitting is visible. The contacts measure 0 ohms when closed (measured with a digital multimeter), and they open properly. The HT coil measures 4860 ohms from the HT terminal to the magneto body.
I thought perhaps the HT coil insulation had failed, so I tested it with a megger (one of the great old mechanical ones). I had to disconnect the "earth" end of the HT coil from the magneto body to do this. The resistance between the HT coil and earth (its iron core) is between 30 and 40 megohms. To me that sounds good.
I also meggered the condensor to see if it had failed in the short circuit condition. It measures 40 megohms.
Can anyone think what might be wrong with this magneto? I really can't figure it out right now.
Many thanks,
Chris
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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
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On Sat, 28 Mar 2009 02:17:49 +0000, Christopher Tidy

Wipac = Wico-Pacey
Peter -- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk http://www.oldengine.org/members/diesel http://www.stationary-engine.co.uk http://www.oldengine.co.uk
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Take all the "Plastics" off,give it a good cleaning inside,check any connections, give it a good "Cooking" on top of your hot water tank or radiator, replace the condenser as a matter of course and it will stand a better chance of working, if not then You can suspect that the coils faulty,

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What about the strength of magnetism in the magnet?
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Good point!! Did anyone ever make a "Gaussmeter" or do we have to rely on seeing how many bolts it will pick up?? Personally I'd be inclined to bundle it up and send it to Martin Percy. I sent a GK2 mag. to him a few years ago and he made a fantastic job of it, not expensive either!!!

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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.
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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

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kimsiddorn wrote:

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
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Charles Hamilton wrote:

Is this Camping Stove Man?
Chris
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No this is Charles, campingstoveman is Martin! Just had a quick look on ebay and they do make Gauss meters, if you've got 180 to spare!! Looking at other posts on ebay apparently you can use a gauss meter to hunt for ghosts!!

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Charles Hamilton wrote:

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
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OK. I've caught up now!! No, they are different people. I don't think I've ever seen a posting from Martin Percy on here(?)

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Charles Hamilton wrote:

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
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Jet Fitter wrote:

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
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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

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kimsiddorn wrote:

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
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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
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jagojules wrote:

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
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Christopher Tidy wrote:

I decided to take a chance on a used magneto, and scored one on eBay: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item50185394173
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
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