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Magneto coil gap.
Posted: Tue Jun 23, 2020 5:15 pm
by ModelT46
Book states 20 to 40 thousands., with more gap of 6 to 10 thousands on lower side due to weight of the transmission. When can the gap be to much. I put in a new field coil. The transmission is a non starter one from about 1917. The field coil is a single stack. The coil and trans are now in. The gap ended up at 48 thosands at top and close to 60 thousands at the lower side. I know this more than should be. Will the mag still produce current with these larger gaps?. The magnets seem strong.
Re: Magneto coil gap.
Posted: Tue Jun 23, 2020 5:29 pm
by Kerry
It will only get weaker in voltage as the miles clock up. Why didn't you make it right when it was apart?
Re: Magneto coil gap.
Posted: Tue Jun 23, 2020 5:50 pm
by ModelT46
we thought it was closer.
Re: Magneto coil gap.
Posted: Tue Jun 23, 2020 6:07 pm
by Susanne
You might be able to correct it with a 3rd main cap designed to take up the clearance... but it will then be one of those things you will need to keep an eye on.
.060 is huge, and will mean your mag will be perpetually weak... sorry!!!
Re: Magneto coil gap.
Posted: Tue Jun 23, 2020 6:55 pm
by Mark Gregush
The instructions are published in more them one place along with postings here. Do it right the first time.
Re: Magneto coil gap.
Posted: Wed Jun 24, 2020 11:56 am
by jab35
Sorry for the bad result. The gap problem is made worse by the fact magnetic 'coupling' is a function of the square of the gap distance, not a simple linear function of distance. Unfortunately, fixing the gap is a big deal, but likely will be necessary for the engine to run properly. Best, jb.
Re: Magneto coil gap.
Posted: Wed Jun 24, 2020 2:57 pm
by Altair
Why can't the coils be shimmed to reduce the gap, there are variable thickness shims available that are inserted behind the three bolts holding the coils.
Re: Magneto coil gap.
Posted: Wed Jun 24, 2020 3:13 pm
by John kuehn
Getting the mag gap is a trial and error adjustment when the engine is on the stand with the pan off. Add the shims then move the engine in the horizontal position to check if if the transmission weight changes the adjustment. If it does go back and add or remove shims accordingly. You can do it also by just installing the flywheel only and then after the adjustment is done add the drums.
Some folks do it that way not realizing that the entire transmission weight will change the adjustment.
Either way you do it that’s the time for trial and error to get a reasonable adjustment like the manual says.