Wico A Magneto faults

[trusty220]

Last weekend I was seriously doubting my sanity and nearly put up my cherished 3-speed Trusty for sale because I was so fed up with it.
What had happened was this: last time I used it in anger was at Weeley two years ago when we all ploughed in line on the Sunday afternoon, then loaded up and went home before the threatened rain came. Rain?? It was like driving in a washing machine, so the Trusty got very wet on the trailer and resisted all attempts to start it ever since. It then got sidelined because I was spending more time at weekends looking after my aging father and mother, so by the time I decided to get it going again it had really been neglected.
First thing to do was to take the magneto home and give it the treatment. Points were removed and dressed on an oilstone and all connections cleaned up and checked. Spinning it over with a drill produced a spark, so I thought that I’d chance my arm and put it back on the Trusty. That done, I drained the old fuel out and cleaned the pipework and filters then re-assembled it all, filling the tank with Shell’s finest.
It started after three spins on the strap, then began to run rough as if the choke was still on then cut out. Ah- carburettor, thought I, so I cleaned out the carb and found everything strangely in order. So I put it all back together, spun it on the strap agian and it started again then did exactly the same as before- run rough and stop. This time I checked for a spark and found that it had disappeared. Now, I’ve had this before with other machinery in my workshop days and it always pointed to the coil breaking down under load as it warmed up, so I changed the coil for another second-hand one that I had.
This time it started and ran for about a minute, then ran rough and stopped. Cursing myself for choosing a duff coil, I fished around and found another second-hand one which I put on. Same result.
This was too much of a coincidence, so in desperation I decided to change the condenser and run it on the lathe to test it. This time it worked and stayed working all through dinnertime, so I put it back on the Trusty and found that it had been cured.
Back to work on Monday morning I was relating this to Ray who used to work with me and he said that he would have done exactly the same- coils tend to break down slowly under load, but condensers either worked or they didn’t.
Trust me to get the exception to the rule!
I have now successfully rebuilt completely a Wico A magneto from scratch to fit to a new show tractor; this includes the impulse starter and removal of the armature. Is anyone interested in seeing how it’s done?

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[ransomes256]

I have been rebuilding Wico A magnetos fitted to Ransomes crawlers for a number of years and apart from coil faults can confirm the failure you describe is often associated with the condenser. It is true a condenser normally works or does not but some condensers can take a considerable time to accept a charge and also a slow rate of discharge. I am not aware why this occurs but a new condenser will charge and discharge quickly.
Neil

[Author]

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