Ford V8 ignition resistor question

Bruce Parker (RIP) · #1 30-05-09, 05:19

I gave my carrier a good run today and it's doing what it's always done...quit when it gets too hot. The rad and timing is OK and I think the problem is in the ignition resistor. I have the original early clam-shell distributor and a Ford 'F8 tractor' resistor in the dash. Starting from cold is no problem. Once warm (hot), the ignition resistor gets too hot and prevents current from getting to the coil. If I jump the resistor, the coils gets too much current and runs too hot. What the frig do I do to fix this???

Lynn Eades · #2 30-05-09, 09:22

I dont really know, but it sounds like your coil is faulty.I heard somewhere that a lot of the old ford coils fail like this. If you put a volt meter on your resistor, I doubt it will change from cold to hot. I'd guess there is a short in the primary windings of your coil, and its drawing too much current, which is why the coil gets hot.

NORTH-SHORE(CANADA) · #3 30-05-09, 09:32

Hi Bruce
After your run the motor turn tight ?? are won't start??

Mike Kelly · #4 30-05-09, 10:21

Quote:

Originally Posted by Lynn Eades

I doubt it will change from cold to hot. .

Resistors definately change value with temperature .. a known fact .

The small resistors up to 1 watt in rating you see on many boards are made from a carbon based material ..for higher power dissipation , they use wire wound resistors , these are typically a special kind of wire , wound on a ceramic or similar material . The wire used in those old home electric bar heaters or old style jug elements, has a cold resistance value , and a hot value .

The Ford coil resistors are dropping around 3 volts ..with 2 or 3 amps flowing through it all day .. 3X3 = 9 watts .. doesn't sound much but that small resistor has to handle all that power and it becomes very hot . The voltage regulators are set to about 7.2 or 3 Volts and the coils are rated at 4.5 Volts I think. Its designed for easy starting on those freezing winter mornings . As the starter motor turns over , its pulling massive amps and the battery voltage drops down to about half its resting state .

the best solution is to install a resistor with the same ohms value, but with a bigger wattage rating ..maybe a 20 watter ...this would run cooler and not restrict the current so much. I'd look for an old electric bar heater and salvage the wire from the bar ..find a big round ceramic former and wind a new resistor .

Mike

Mike

Phil Waterman · #5 30-05-09, 16:04

Playing with Ford or Lincoln Flat Heads as hot rods we had a couple of cures for hard starting. One an electric fuel pump back by the tank to push fuel up to carb before trying to start, also good for clearing vapor lock. The other was a switch to by pass the resistor so that for starting you could get full voltage. They even sold a solenoid that had a side tap so that when the starter was turning full voltage went to the coil.

On my hot rod Lincoln we removed the manual fuel pump completely and went straight electric with a separate switch under the dash. Great anti theft device and if you did flowed the engine you could turn off the pump push the gas peddle to the floor and hold it while you cranked the engine once it cleared the excess gas the engine would almost always start and you would then turn the pump on. Pump of course was in series with the ignition switch so that it would never run when the ignition was off.

rob love · #6 30-05-09, 18:56

If it is quitting while running, and quite hot, and there is still fuel going to the engine (no vapour lock) then my money is on the coil. They will work when cold, and not once they heat up. Is yours the distributer with the coil right on the distributor?

Those are a tough (and expensive) coil to find these days. Options are to install one of the adapter plates and relocate the coil to the top of the engine, or to change to the later distributor with the coil located on top of the engine.

A similar coil is readily available for the 9N tractor. I saw them the other day right on the shelf at the local TCS store. I may try to adapt one of these onto the early V8 distributr. Seems to me a sheet metal adapter plate could possible be made to adapt it.

Mike Kelly · #7 31-05-09, 03:52

I still have two of the trouble prone 6 Volt divers bell coils ..if anybody wants one . I see them at swap meets too..they are not worth much really . A NOS example I bought when I had the Ford, is a aftermarket brand , not FORD, but made in Sydney NSW. The little brass post for the primary wire is sometimes broken off , as it protrudes out above the main body.

A local here runs a 6V external coil , with an adapter that fits to the top of the diver bell coil.. it runs very well without the usual heat up trouble.