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Farmall & IHC Tractors Discussion Forum
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H magneto timing problem

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mikeinWA

01-28-2006 15:19:01




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I have a 1940 H. It has jumped time twice. Twice I have switched the plug wires 180 degrees, and twice that solved the problem; the first time for almost a year and the second for about a month. Now it did it again and no matter what I do I cannot get the timing within more than 40 degrees following the IT manual. The magneto seems functional (it is actually a battery ignition with an external coil), I have gone so far as to pull the timing cover and cam gear and everything looks good. What is causing this???? Any help will be greatly appreciated.

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Bob

01-28-2006 15:28:49




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 Re: H magneto timing problem in reply to mikeinWA, 01-28-2006 15:19:01  
Is the system a "gutted-out" mag, and OEM IH distributor, or and aftermarket distributor conversion kit?



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mikeinWA

01-28-2006 15:35:07




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 Re: H magneto timing problem in reply to Bob, 01-28-2006 15:28:49  
Its a gutted out mag.



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Bob

01-28-2006 15:49:24




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 Re: H magneto timing problem in reply to mikeinWA, 01-28-2006 15:35:07  
As I told the other guy with timing troubles, the slots in the mag drive on the engine must be horizontal (- -) when #1 is at TDC of the firing stroke.

Does the impulse coupling work on your gutted-out mag? This might not seem important, because it is no longer a mag, needing the "snap action" for a good spark, but it IS important.

When the engine is just being cranked over, the impulse will grab, and then "snap", giving a starting timing of near TDC.

As the engine "catches" and speeds up, the impulse will no longer catch, and the timing will advance to "running timing", probably 30+ degrees.

So, when you are turning it over by hand, and come up on #1 TDC on the firing stroke, the impulse will wind up and "snap", opening the points, and giving a spark at about TDC.

If the impulse does NOT grab, and then snap at TDC, the spark at slow cranking will be 30+ degrees too early. If it were still a mag, and the impulse failed, there would be little, if any spark while cranking slowly, however, with this conversion to Kettering ignition, any time time points OPEN, there will be a hot spark, even with a failed impulse.

If the impulse is REALLY working, and it's getting out of time, the possiblilites are:

1.)Something wrong with the timing gears/mag drive. This can be checked by verifying the drive slot is horizontal at TDC.

2.)The impulse is keyed to the mag shaft... could be problems there.

3.)There could be a problem with the rotor drive gears in the mag... little gear loose, or wear and tooth damage.

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mikeinWA

01-28-2006 18:23:09




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 Re: H magneto timing problem in reply to Bob, 01-28-2006 15:49:24  
Thanks for the response. Turns out it was a sheared woodruff key in the mag drive. It must have caught at one point and allowed me to time 180 out, go figure.



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