I have a 1950 Farmall Cub with a 12v conversion. This year it seems to be using up distributor points at an unusual rate. With the tractor running very poorly last Spring, I replaced the points and all was well, but now it is doing the same thing (bad irregular miss).I burnished the points with a quick swipe of a small file and it is better, but what would make them go bad so quickly? Usually they last for years and have to be replaced only when the spring breaks in my experience, but to have the same problem within 6 months is very odd. Could this be related to the condenser or coil? Both were replaced last Spring when I was troubleshooting the problem then.
- Thread starter BearGap
- Start date
Typical causes are excess points current and/or a bad condenser.
When it was converted to 12 volts was the old 6 volt coil still used??? and if so was an external series voltage dropping (12 down to 6) ballast resistor added???? If its still a 6 volt coil unballasted it will overheat and the points burn up quickly.
Put a voltmeter on the coils input (NOT the terminal to distributor) and turn ign on and when points are closed read the voltage?? If its a 6 volt coil you need 5 to 7 volts or so (because a proper ballast would drop the other 6 volts). If it was replaced with a full true 12 volt rated coil (NO ballast) then Id expect like 12 volts.
If the coil is correct try a new condenser. If its still a 6 volt coil see how hot it runs???
John T
When it was converted to 12 volts was the old 6 volt coil still used??? and if so was an external series voltage dropping (12 down to 6) ballast resistor added???? If its still a 6 volt coil unballasted it will overheat and the points burn up quickly.
Put a voltmeter on the coils input (NOT the terminal to distributor) and turn ign on and when points are closed read the voltage?? If its a 6 volt coil you need 5 to 7 volts or so (because a proper ballast would drop the other 6 volts). If it was replaced with a full true 12 volt rated coil (NO ballast) then Id expect like 12 volts.
If the coil is correct try a new condenser. If its still a 6 volt coil see how hot it runs???
John T
I should have mentioned that the 12v conversion is pretty old, more than the 20 years I have owned the tractor, but these last 2 instances are the first where the points seem to be getting messed up. The coil has always gotten hot, or at least pretty warm, and I did put in an identical replacement along with both (?) condensers last Spring. It has one condenser in the distributor, and another external one that attaches to the coil bracket. I never understood why it needed 2.
These happened while the alternator had been accidentally disconnected when the tractor was split last Spring. After running on battery only all summer, I noticed it wasn't charging and found the lead (with a diode somewhere in the circuit) back to the ignition was not connected. I repaired that and then found the points burned up again. may not be related, but full disclosure.
These happened while the alternator had been accidentally disconnected when the tractor was split last Spring. After running on battery only all summer, I noticed it wasn't charging and found the lead (with a diode somewhere in the circuit) back to the ignition was not connected. I repaired that and then found the points burned up again. may not be related, but full disclosure.
old
Well-known Member
- Location
- Camdenton Missouri
Now days most parts are made poorly so if you buying cheap points and condensers that is where your problem is you need a good brand name part. Next 50% of new condensers are bad right out of the box and I have now replaced one in years due to that fact. As for how old the conversion is that does not matter unless you have a shorted ballast resister which is not likely since they burn out instead of shorting out
Bob M
Well-known Member
Like John T says, the coil getting hot and the points burning out indicates excessive coil current. (The coil should become just slightly warm after a long run.) Wiring a ballast resistor in series with the coil primary should solve both problems.
Incidentally the condenser on the coil bracket is not needed. Some older cars used a second condenser on the coil; also sometimes on the genrator, alternator or voltage regulator. It was provided to reduce RFI (static) on the car's AM radio.
Incidentally the condenser on the coil bracket is not needed. Some older cars used a second condenser on the coil; also sometimes on the genrator, alternator or voltage regulator. It was provided to reduce RFI (static) on the car's AM radio.
I don't know if the coil was changed with the 12v conversion, but I suspect it was as it was identical to a coil in a 74 GMC truck we had. Still, I did not see a ballast resistor and there was 12v at the coil when the ignition was on, so I picked up one at Autozone and installed it in series with the 12v from the ignition. I filed more on the points and put everything back together, and it started and ran smoothly. I'll have to see if that lasts. I'll see if maybe I need to change the condensers, too. In hindsight, the plug wires got changed as part of the shotgun approach to trying to fix the problem last Spring, and now I wonder if they were resistor wires before. Still, until I changed points it continued to miss then, but it had run well for the previous 20 years.
Thanks for all the helpful comments. Sometimes it is a bit of a mystery working on these 60+ year old machines, especially when they have modifications.
Thanks for all the helpful comments. Sometimes it is a bit of a mystery working on these 60+ year old machines, especially when they have modifications.
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