H4 Magneto won't spark at starting rpm

loch · Aug 28, 2015

I have an Int'l H4 magneto that someone long ago shoehorned onto a Continental F162 (Lincoln SA200 Shorthood welder). I've overhauled the mag, new points and condenser, it is an "L" (CCW) and I timed the rotor shaft and points cam according to the service manual. The magneto sparks like crazy on the bench, and turned at high RPM's (More than 60, counting from the rotor spindle). However, at starting RPM's, which are about 60, there is no spark. Is the reason a weak coil? The impulse spring and counterweights all seem fine, and moving properly. The actual engine timing and all the other timing (governor timing, rotor timing) is correct as far as I can tell and have triple checked.

Thanks for the help!

Den N Ms · Aug 28, 2015

Loch,Check and make sure that the impulse is working and tripping properly.Check it with the mag mounting flange in a vice,turn with a crescent wrench and check spark with a old plug hooked to a wire and grounded to the vice.The mag should spark upon impulse trip. Fairbanks Morse h4 mag?

loch · Aug 28, 2015

I wish there were such a thing as a Fairbanks Morse H4 mag. (Maybe I have the only one!) No, this is an International H4, like the ones that go on Farmall Tractors. It is crazy how it fits on the F162. I wonder if long ago, the Int'l mag was somehow mounted to the FB mounting flange.

It gets crazier. According to all the serial numbers on the mag, and according to the big "L" stamped on the impulse drive, this is a CCW mag. (CW mags are stamped with an "R", for "right" as in the direction of movement.) But, it only turns clockwise, which is good, because the F162 turns clockwise. The Int'l magneto service manual does explain how to get a CCW mag to turn CW, so I guess this mag was reversed when it was made to fit onto the F162.

This is all crazy, but really, it shouldn't matter. The mag makes spark at high RPM's, and not at low RPM's. I'll check out the impulse, like you said. If all else fails, I'll just buy an FB mag.

JMOR · Aug 28, 2015

When observing spark on the bench, are you observing at the connections for the 4 plug wires or elsewhere?

gene bender · Aug 28, 2015

All they did was to change the mounting plate on the H-4 for the Cont engines due to space you can change that plate and use one from a tractor or change the one on the Cont engine to tractor flange. I did that and its still running

gene bender · Aug 28, 2015

The rotor in the mag can be rusty and same with the field coil cleaning up both will sure make more spark. Have you cleaned the impulse end in kero or diesel mite be dry or too gummed up for the dogs to lock good as the impulse should have a good snap when it trips. I use a gear that has the female end that drives the mags. I put it in a batt drill so i can vary the speed then having the mag in a vise with wires going to grounded plug so i can give it a complete cycle befor installing on the motor fast slow and starting even slow enough to make the impulse snap at each position 1-4 have wires and all 4 plugs hooked up grounded to bench that way im sure of complete operation when installed.

loch · Aug 29, 2015

Ha, ha, I figured out the mystery!

It turns out the "L" (CCW) mag really IS a CCW mag. Someone, (I'm glad I don't know who) stuck this thing on the Continental engine, and probably gave up when they couldn't get a spark out of it. I turn this thing CCW, instead of CW, and I get a spark a half an inch long! There's nothing wrong with the magneto or the impulse mechanism, or anything else. It's just the wrong mag for the engine, period. I found this Shorthood in the weeds and asked the owner if I could have it. They said sure, and didn;t know or care what it was. I've overhauled the whole generator end of the machine, and was just now getting around to the engine end of it, when I couldn't get a spark out of the magneto. I remember thinking the Int'l mag on a Continental was WEIRD, but I guess it was just there for show, (or something). I'll stick this mag on the shelf, and chalk the whole adventure up to "continuing education". Thanks for all the help everyone.

JMOR · Aug 29, 2015

(quoted from post at 01:29:34 08/29/15) Ha, ha, I figured out the mystery!

It turns out the "L" (CCW) mag really IS a CCW mag. Someone, (I'm glad I don't know who) stuck this thing on the Continental engine, and probably gave up when they couldn't get a spark out of it. I turn this thing CCW, instead of CW, and I get a spark a half an inch long! There's nothing wrong with the magneto or the impulse mechanism, or anything else. It's just the wrong mag for the engine, period. I found this Shorthood in the weeds and asked the owner if I could have it. They said sure, and didn;t know or care what it was. I've overhauled the whole generator end of the machine, and was just now getting around to the engine end of it, when I couldn't get a spark out of the magneto. I remember thinking the Int'l mag on a Continental was WEIRD, but I guess it was just there for show, (or something). I'll stick this mag on the shelf, and chalk the whole adventure up to "continuing education". Thanks for all the help everyone.

eally, now??? What happened to this declaration; " But, it only turns clockwise, which is good, because the F162 turns clockwise. "??

H4 Magneto won't spark at starting rpm

loch

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Den N Ms

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loch

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JMOR

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gene bender

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gene bender

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loch

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JMOR

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