Magneto, heal thyself?

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Model T Ford Forum: Forum 2015: Magneto, heal thyself?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Jared Buckert on Thursday, April 02, 2015 - 09:48 am:

So far I've only had my roadster pickup out twice this year. Sad, right? Anyway, the second trip was approximately 9 miles before it got too dark to safely run. On a lark, I switched the key over to mag. When running at speed, I couldn't tell a performance difference between mag and bat. It was only when I slowed down that she seemed to stumble.

I've done zero work on the magneto with this car. When I bought it, there wasn't even a wire to the mag post. After installing the new wiring harness, I've tried mag a few times. Never gotten that kind of performance out of the magneto. I highly doubt elves are recharging my magneto overnight, so I'm kind of curious. Anybody have any theories?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Val Soupios on Thursday, April 02, 2015 - 09:55 am:

Higher RPM's allow a weak magneto to put out enough for the coils? Your magnets may be weak or you have excessive end play. An in car magneto charging may help and I have used the front end shim the vendors sell to address the end play issue as a stop gap measure. The combination has given me another few years of driving on mag while I prepare for a total drive train rebuild


Top of pagePrevious messageNext messageBottom of page Link to this message  By Adam Doleshal on Thursday, April 02, 2015 - 10:52 am:

If it runs okay on mag in high gear at any speed, but stumbles as soon as you put it in neutral, (and/or low, or reverse), then the issue is excessive end play.

If this is the case, pull the inspection pan and replace the third main and fit a new one to take up the end play. If you belong to a local club, there are probably at least a few guys that drive their T's quite a bit and have done this once or twice and should be willing to help. It generally only takes about two hours start to finish.

I'm not a fan of the thrust devices that go behind the front crank pulley unless it is used on a car that literally doesn't get driven more than maybe 20 miles a year. Every time you are in neutral, low, or reverse the clutch spring is compressed and there is around 100 pounds of pull straight back on the crank shaft. If your thrust area is at the very front of the crank instead of at the rear as it should be, there will be some improper flexing going on in that crank shaft that may reduce its longevity...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Henry Petrino in Modesto, CA on Thursday, April 02, 2015 - 11:00 am:

I could be that the absence of a wire to the mag post was the result of it not running on mag, but because the wiring was flawed elsewhere and the mag itself worked all along. Perhaps a previous owner just assumed the mag didn't work and didn't want to fool with it. When you installed the new wiring harness you fixed the problem without realizing it.

Anyhow, it's a possibility. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Thursday, April 02, 2015 - 11:03 am:

Before you do any of the above, check the magneto output with an AC analog voltmeter across a 12 volt lightbulb while running on battery. If the output is over 6 volts at idle and increases with speed Your problem could be the coils are not tuned for magneto. It's possible that even the timer could need replacement.

If you find the magneto output to be low, then try to pry the crankshaft forward by using a large screwdriver between the front engine plate and the pulley. Don't pry too hard, you don't want to bend anything. First depress the clutch which will move the flywheel and crankshaft back as far as it will go, then let out the clutch to high position and go front and pry the pulley. If it moves noticeably, you have endplay.

Then if you have endplay, replace the rear main cap. If that doesn't fix it, recharge the magnets.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Thursday, April 02, 2015 - 11:38 am:

I agree with Norman. Check the coils on an HCCT type tester to see if the operate current is correct and that there is no double sparking because from my experience your symptoms match very well with incorrectly setup coils.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jared Buckert on Saturday, April 04, 2015 - 11:05 am:

I had the coils rebuilt three years ago by the Coil Doctor. Haven't messed with them since. Would running on battery have any effect on the coil's performance on magneto?

I will look for some parts and build one of the light bulb test devices. Pretty sure I have all the parts somewhere. Just have to put them together and test it.

One of the joys of having weather good enough to go for a motor in an old car is there are a lot of other things needing done outside. I will try to get into the garage and see what I can find. Thanks for all the help.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Saturday, April 04, 2015 - 12:38 pm:

A bit of thread drift Jared, but did you modify your pickup bed so that you could lower your top? If you posted your solution a while back, I missed it. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jared Buckert on Sunday, April 05, 2015 - 09:13 pm:

Not yet, Mark. It's on my to do list. Along with finish up the paint on my wheels and buy new tires. Thanks for reminding me! haha


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