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Post by deverett on Apr 14, 2009 19:10:33 GMT
I have acquired an ETW Centaur engine that uses an Atomag magneto for the ignition. But there is no spark at the plug. The engine looks like it has run in the past.
Can anyone give me a troubleshooting guide on what to look for and how to test the various components, please?
The easy solution would be to put a conventional ignition system on it, but that will be the last resort.
I write this while idling my time out in Saudi. I can't carry out any M.E. activities here, so think up lots of jobs to do when I get home. Problem is that very few of them ever get fulfilled and the list just gets longer each time I come out!
Thanks in anticipation.
Dave
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Post by baggo on Apr 14, 2009 19:46:33 GMT
Hi Dave,
The obvious things to check are the condenser and the coil windings. You can measure the windings with a meter to check that they are not open circuit. The condenser is a bit more difficult but should hold a charge if you connect it across a battery. Dab it across, remove, and then measure the voltage across the leads. It might be easier to try another one if you have one to hand. Also the timing is critical in that the points should open when the magnetic flux in the coil is at it's peak.
Is it the later magneto with the commercial coil or the earlier version with the home wound one? There is a two part series on building the later version in ME vol. 124 issues 3124 and 3128.
John
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Post by deverett on Apr 15, 2009 13:26:48 GMT
Thanks for the pointers, John. When I get home it will be on the priority list.
The Inishannon (Co. Cork) vintage rally is on for the June bank holiday (actually 30, 31 May - well, it is Ireland!) and I would like the engine running for the show.
Got to get home first.
Dave
The Emerald Isle
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Post by deverett on Apr 15, 2009 13:30:24 GMT
John
I should have completely read your reply before answering.
The coil (as far as I remember) is a commercial item and unfortunately, I don't think I have the relevant M.E.s.
Will check all when I get home.
Dave
The Emerald Isle
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Post by baggo on Apr 15, 2009 13:56:06 GMT
If you haven't got them, let me know.
John
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Post by deverett on Apr 19, 2009 18:56:22 GMT
I'm daft - but there's no need to confirm it!
I got home yesterday and had some time out in my workshop today. Got out the engine and did some tests a la Baggo. The first thing I find is that the mag is not an Atomag, its a Minimag! My memory is failing fast.
I got out my Bob Shores book on 'Ignition Coils and Magnetos' and read up the bit about magnetos. It seems that the Minimag has got a condenser built in.
I have checked continuity between the two leads and ground and between the two leads and all read 0 ohms.
I am wondering whether the leads are wired correctly. The HT lead goes to the plug - there is no possibility of error there. Ground is through the body of the magneto. The LT lead goes to the points, but where exactly on the points should it go?
It strikes me there are two possible reasons for no spark: 1 The condenser is duff or non existant or 2 The LT lead is in the wrong place on the points (or both). At the moment, the LT lead is connected electrically to the moving point. Is this correct?
If the condenser is bad, I could always put an external condenser in the system.
I believe Jim Shelley of Minimag has ceased trading, but I don't know if the business was sold on or it has been lost forever. Does anyone know the situation regarding the business? If it is under new ownership, I could possibly get some help from that source.
In the meantime, any (other) ideas would be most welcome.
Dave
The Emerald Isle
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Post by baggo on Apr 19, 2009 19:26:26 GMT
Hi Dave,
I would expect to see a high resistance on the HT coil (between the plug connection and ground) as this will consist of several thousand turns of very thin wire. Zero Ohms suggests that it's got a short to ground (or the LT coil) somewhere?
I would imagine the LT connection will go to the moving contact. The fixed contact will be connected to ground. It could be the other way around though I suppose. Either way, the coil connection should go to the contact that is not grounded.
It was announced in ME for May 2007 that the Minimag business was up for sale but I don't know what happened to it. There is no further mention of it in ME.
John
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Post by deverett on Apr 19, 2009 21:10:53 GMT
Hi John
Thanks for the helpful reply.
When I got the engine, the LT lead went to the ground side of the points. Realising that the moving point was not in circuit, I changed it to the moving contact side.
0 ohms on HT = bad coil? I'll check it one time more again tomorrow, but it seems as if I will be looking for a new magneto!
Back to the drawing board...
Dave
The Emerald Isle
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Post by baggo on Apr 20, 2009 9:37:07 GMT
You could try flashing 6 or 12 volts across the LT coil and see if that gives you a spark at the plug. If not, there's a good chance the coil is dead  John |
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Post by ettingtonliam on Apr 24, 2009 12:21:59 GMT
I built a Centaur a good few years ago, and the standard ignition system was coil and battery, not magneto. It used a set of Lucas car points with a cam on the sideshaft.
Richard
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Post by deverett on May 1, 2009 7:42:23 GMT
I took the engine along to a model show last weekend and someone with experience in 'full size' magnetos had a look at it. All Is OK with the magneto, I was not rotating it fast enough to generate sufficeint juice to create a spark.
The standard igniton suggested by ETW may have been traditional points and coil, but the builder of my engine obviously wanted to use a magneto system for his version.
Thanks for all the helpful suggestions. All's well that ends well.
Dave
The Emerald Isle
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