Measuring Model T engine rpm using magneto frequency?

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Model T Ford Forum: Forum 2015: Measuring Model T engine rpm using magneto frequency?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Gail Lanning on Saturday, October 10, 2015 - 04:38 pm:

Wondering if anyone has done this using a digital multimeter (DMM) with a frequency scale? I tried once, but I suspect the magneto voltage may have been to low to be picked up by the DMM. The frequency I think should be 213 1/3 hz @ 1600 engine rpm. That is calculated by 16 poles/magnets X 1600 rpm divided by 120. Thoughts


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thomas Mullin on Saturday, October 10, 2015 - 04:50 pm:

Gail,

Wouldn't there be a pulse for every magnet pass?

Then for 1600 RPM there would be 25,600 pulses per minute or, dividing by 60, 426 2/3 cycles per second. I don't think you need to count the positive and negative parts of a cycle separately.

Where's John Regan when we need him?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Fred Dimock, Newfields NH, USA on Saturday, October 10, 2015 - 04:58 pm:

I'm betting on Hershey.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Garnet on Saturday, October 10, 2015 - 06:13 pm:

Buzz Pound made tachs with a 270 analog meter. Versions were available for dizzy points or magneto frequency. I dearly wish they were still available.

Regards,
Garnet


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie Spokane, WA on Saturday, October 10, 2015 - 07:14 pm:

Gail is right, 1600 r.p.m. is 213 1/3 hz. It still can be done and was done by Buzz Pound as pointed out by Garnet. It doesn't work with Ruckstells in low, or low pedal and such. For me it is nearly as easy to hook up a bike speedo, or even easier yet, use a GPS.


Top of pagePrevious messageNext messageBottom of page Link to this message  By JohnH on Saturday, October 10, 2015 - 07:16 pm:

The magneto testing function in the ECCT works on this basis.

magtest

Multiply frequency by 7.5 to get rpm. Some digital instruments are affected by the Model T ignition system so this needs to be kept in mind when attempting to measure the magneto.


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