1945 farmall a, no spark problem

• Magneto Service Information

THANKS AGAIN !!

To access the points, the whole end of the mag comes off, including the 2 snap straps that hold the cap in place.

This assembly is held on with THREE screws.

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Pleasantries aside, my money is on corroded or otherwise messed-up breaker points in that old mag.

When a tractor sits a long time it's not unusual for moisture, etc. to get inside corrode the point contact surfaces resulting in a "no spark" condition.

Let us know what you find!

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!

I have attached my complete n long winded Troubleshooting Procedure for non sparking buttttt t before I dug too deep I would install and gap a new set of ignition points (or try to clean n gap the old ones, then she might fire???) and condensor located under the distributor cap and clean and check the cap n rotor. Next thing is you gotta have voltage to the coil when you turn an ignition switch ON.

Insure voltage to the coils input (NOT to distributor) terminal when switch is on then check n clean (use points file to dress them up clean n even) or replace n gap the points and see if she fires then. If NOT see below....

TROUBLESHOOTING A BATTERY POWERED EXTERNAL COIL TYPE IGNITION SYSTEM:

PRELIMINARY CHECKS:

(A) To see if it happens to be a cap n rotor problem and to see if at least the coil is firing, remove the coil wire from the distributor (leave coil end intact) and place its bare end to within 1/8 inch from tractor iron, turn her on n crank her over, and see if she jumps that gap with a good visible blue spark????? If so but the plug wire ends (from wire end to 1/8 inch to frame) or the plugs themselves don’t fire, its a cap n rotor or plug wire problem. If the coil wire isnt even sparking, see below.

(B) Next open the cap and see that the points are gapped correct and indeed opening and closing as the engine is cranked and the distributor shaft rotates and MAKE SURE THEY ARE NOT BURNED OR PITTED OR CARBONED UP BADLY !!!!! !!!!! If so, running a point file between them to clean them up might make her run again HOWEVER that’s only a temporary cure, so if that cleaning makes her spark, INSTALL N GAP NEW POINTS. In the event they appear good but only gray oxide coated, non abrasively clean/buff/polish them using say a dollar bill or shop cloth etc. and see what happens.

MORE TROUBLESHOOTING IF ALL THE ABOVE STILL FAILS TO MAKE HER SPARK

1) THE VERY FIRST THING YOU GOTTA HAVE is voltage to be present on the coils high supply (NOT to distributor) terminal when you turn the Ignition switch ON. If not she cant ever fire, but in the event the ignition switch or circuit/wire down to the coil or any Ballast Resistor is bad or open, you can HOT WIRE it by jumping a hot ungrounded battery voltage source to the coils high input supply (NOT to distributor) side n see if she runs then???? If she fires hot wired, you could have a bad ignition switch ((That can happen, when Ignition is on, the switches IGN terminal must turn hot)),,,,, ,or an open Ballast (if it has one) or a bad/open wire from switch to coil.

If the switch is good, if you turn the ignition switch on and place a test lamp on the coils high (NOT to distributor) terminal SHE MUST LIGHT UP. If not again, look for an open Ballast Resistor (if it has one, it should read around 1.25 to 2 ohms across its terminals) or bad/open wires from the switches IGN output down to the Ballast (if it has one) and distributor.

2a) When the Ignition switch is turned on, voltage should appear on the coils high input side. That would be 6 volts on a straight 6 volt system or 12 volts on a 12 volt non external ballasted system, or around 6 volts on a 12 volt system that used a 6 volt coil plus an external Ballast Resistor and the coil is good and the points are closed and they and ALL wiring is good.

2b) To insure the coils low voltage primary winding is not bad/open, use an ohmmeter and measure its DC resistance between its lil + and -terminals. If its an open circuit (no continuity) its bad/open and will NOT work. It should measure around 1.25 to 2 ohms or so if its a 6 volt coil and maybe 2.5 to 3.5 if its a 12 volt internally ballasted coil. NOTE CAUTION have all leads and any voltage source DISCONNECTED FROM the coil for this simple primary winding continuity test. 3) Next, place your voltmeter or test lamp over on the coils other low to distributor terminal side, turn her on and crank the engine over.

4) A test lamp there should flash ON (when points are open) and OFF (when points are closed) as the engine is cranked slowly.

5a) If the lamp never comes on there, the coils primary is bad/open,,,,, ,,,,or the points are never opening,,,,, ,,,or theres a shorted/bad condensor (remove its lead to points and see if lamp comes on, if so, bad shorted condensor or its wiring),,,,, ,,or the points wire is shorted,,,,, ,,or the distributors side pass thru stud is grounded (use ohm meter to test that),,,,, ,,,or the points may have a shorted spring.

5b) If the lamp never goes off as engines cranked, the points are not closing or are bad,,,,, ,,or the wire or circuit is missing from the distributor to the points,,,,,or the distributors not well grounded to the tractor.

She cant fire the coil unless its low side is getting a conductive ground return path via closed points and then the circuit is open when the points open.

Be sure the condensor or its wiring is NOT shorted out and see if the lite comes on (when points open) with the condensor disconnected. If removing the condensor makes her spark, replace the condensor.

SUMMARY

Be sure the points are closing fully and open on high cam and ARE NOT BURNED OR PITTED OR CARBONED UP BADLY,,,,, ,theres voltage present on distributors high side at all times when ignitions on (or its a bad switch or open ballast or bad wiring to col),,,,, ,voltage on coils low side flashes on and off as distributor is cranked,,,,, ,,,condensors not bad/shorted,,,,, ,,no shorts in wires to points and no shorts in pass thru side out distributor stud,,,,, ,,coil has continuituy.

You may luck out n just need a new set of points. If the coil wire fires (see above) and the plug wire ends to 1/8 from frame but NOT the plugs, they are baddddd ddddd . Check them BOTH.

Good Luck n God Bless, post back any questions and your findings and any questions.

John T Nordhoff in Indiana, retired electrical engineer who usually lurks over on the Mother Deere boards versus over here on the “dark side”.