Re: 1945 farmall a, no spark problem

Posted by Bob M on August 08, 2007 at 06:48:23 from (151.190.254.108):

In Reply to: 1945 farmall a, no spark problem posted by Packer Fan on August 08, 2007 at 03:28:52:

As the others point out below someone modified the old magneto to work as a standard coil & distributor ignition. It's a commonly found "field repair" done to balky IHC magnetos by frustrated owners.

Here's a quick step-by-step you to isolate the problem:

1 - Pull the high tension wire from the center nipple on the magneto distributor. Stick the wire on a good spark plug, lay the plug on grounded metal, then turn on the ignition and crank the engine. If a spark appears at the plug the problem is the magneto rotor is out of time with the engine.

2 – If no spark in #1, check all the primary wiring for obvious breaks, etc. Repair as required.

3 – Remove the magneto distributor cover and rotor drive plate assembly to get to the breaker points. Be sure to mark the rotor position before removing so you can reassemble the rotor drive in time! The breaker points behind the drive plate should be closed. (If the points are NOT closed, put the rotor drive plate back on, then turn the crankshaft approx ¼ revolution, remark the rotor position and remove the rotor drive plate again.)

4 – Place one voltmeter probe on a GOOD ground (the grounded battery post is ideal…). Now turn on the ignition switch and place the other probe on the coil primary terminal that’s connected to the ignition switch ballast resistor. The meter should read somewhere between about 5 and 8 volts.

If it shows 0 volts, look for a bad ignition switch, ballast resistor or a break in the wiring.

5 – Now move the voltmeter probe to the other coil primary terminal (the one connected to the magneto breaker points). You should see approx 0 volts with breaker points closed. Now manually open the points - the meter should now show the same 5 – 8 volt reading you got in #4 above.

If the meter shows 0 volts with the points OPEN suspect a bad coil, a short inside the distributor or a possibly a shorted condenser.

If the meter shows 5 – 8 volts with the points CLOSED, the points need cleaning. Either lightly file the points to clean, or replace them with new.

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If all the above check out OK, problem could still be a bad coil (open secondary winding) or possibly a bad condensor.

Good luck!

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