Tractor ignition system

I converted my 1959 Ford 851 from 6 volt generator to a 12 volt alternator. It was easy and I am happy with that decision.
However, after many hours of work the tractor just quit. Sounded like out of fuel problem but it wasn't. Also, the neon spark indicator indicated that all plugs were firing.

I installed a kit consisting of points, rotor, and capacitor and the tractor fired off immediately and runs great again. But, I wish I knew which of those items caused the problem. I tested my points with an ohm meter and they looked good. I don't know how to test a rotor other than by inspection and seeing if the plugs fire. My question is "how do you know that a capacitor is bad"?. Is there a way to test it. I had a weak spark that made me think electrical was ok.....it wasn't.

easy simple way to test a condensor...hook a pair of jumper wires to a good battery and briefly touch other end of wires to condensor...positive to wire end of cond. and negative to case of cond.
unhook battery and the grab condensor case in one hand and grab the wire with the other...if your drawers suddenly feel damp...its good...dont be surprised to get more than one bad one in row out of the box.

If it was converted from 6 to 12 volts, did you add any series voltage dropping (12 to 6) ballast resistor between the ignition switch and input to the coil?? If not, the coil can overheat (too much current and resultant heat) and be damaged plus the points will burn up a lot quicker (too much current being switched) AND/OR GET CARBONED AND BURNED AND RESISTIVE CAUSING A WEAK OR NO SPARK AT ALL.

Did you change the 6 volt coil to a full 12 volt rated coil?? That can be done and no ballast would be needed.

Besides that neon tester, when it stops running test to see if the coil and plugs are ACTUALLY firing, they may not be because the coil is breaking down, especially if youre applying full 12 volts to a coil only rated for 6 and not using any ballast resistor.

It takes a REAL capacitor tester to check a condensor for its value and leakage etc. An ohm meter can show if a condensor is BAD like if its shorted, but an ohm meter cant tell if its actually good (nor its capacitance value) under voltage and warmed up higher voltage conditions. To a DC ohm meter once charged it should read an open circuit but if it reads a short ITS BAD/SHORTED. The "kickback test" using an old fashioned analog ohm mter can give some indication of a capacitors charging and as noted show if its bad cuz its shorted out

Id be insuring when it was converted from 6 to 12 a ballast was added or the coil was changed to a full 12 volt!!!!!!!!!!!! Then when it stops insure the coil and plugs are actually firing !!!

ALSO did you change Polarity (like + to - or was it already -??) when you did the conversion (most alternators use - neg ground) ?? Dont let anyone tell you polarity doesnt make a difference in a coil, sure it still fires if wired at opposite polarity, but not as well as if wired correctly

This is basic electricity

John T

Thanks for the feedback John T

You covered all the correct bases. I am using a 6 volt coil with a ballast resister. And, yes I did change the polarity everywhere. I even added big magic marker notes at the battery reminding myself to connect the ground cable to battery ground.

After the tractor quit I pulled plugs and laid them by their respective threaded ports. I had viseable spark but must admit it was weak. I now know a weak spark doesn't get the job done.

I tested the points with my ohm meter by loosening (after marking the position) the distributor and twisting it back and forth. With the points closed I was reading no resistance. This made me believe the points were ok.

At that point, in desperation, I installed a kit including points, condensor, and rotor. Wallah!!! the tractor started and ran great.

I followed up by checking the timing with a light and it appeared "right on" at 4 degrees advance.

Gary

PS: I am considering converting to a 12 volt coil and getting rid of the resister. Some 12 volt coils advertise an internal resistor...I don't quite understand that.

Since youre now at Neg ground, if its not already that way, Id try wiring the coils + to the switched ignition voltage source (switch, ballast etc) and the - to the distributor.

Coils may be labeled "12 volts" or "12 volts NOT for use with external ballast" and that means just what it says, you use 12 volts on it with no external ballast. If a coil is labeled "12 volts for use with (or requires) ballast resistor" again it means just what it says, use a ballast or it will overheat.

Despite what most lay persons and farmer Billy Bob and his beer guzzling know it all brother in law think, most typical old 12 volt tractor coils 1940's to 60's vintage DONT REALLY HAVE A STAND ALONE DISCRETE RESISTOR HIDDEN AWAY INSIDE THE CAN, their LV primary winding resistance in the neighborhood of 2.5 to under 4 ohms (many around 3 ohms) is derived by how much wire is used and/or the resistivity of the wire. Disect or x ray one and I bet you wont find a stand alone conventional resistor tucked in there somewhere!!!!!!! They did make some real early automotive coils that had a seperation (ringed outside) and a seperate compartment where they indeed did have a resistor, but Ive never seen such on any old tractors (40's to 60's ) and I was a used tractor dealer n saw a ton of old tractors n coils.

PS a "good" spark ought to arc 3/16 of an inch and be bright visible blue NOT faint thin wimpy yellow you can hardly see !!!!!!!!!!

John T

With respect, 12 volts will not wet your pants. Skin just has too much resistance. To have a charged condenser, (that you can jet a jolt from) it needs to be charged with 50 plus volts. 150 is actually going to do a good electroshock source. Condenser testers will charge them. Jim

Better listen to Jim. A battery isn't enough to charge a condenser. I have a tester that plugs in to 110 volts that tests and charges them.