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.

Bruce Parker (RIP) · #8 31-05-09, 04:46

The problem is consistent in that it always starts great from cold. It never quits while running, but after a good run if you shut it off, it won't go (lots of gas, not so much spark). The resistor in the dash is burning hot and the coil on the top of the distributor is nice and cool (though I'm touching the plastic case and not the windings on the inside).

I like the idea of an eternal coil, one with an internal resistor wired through a dummy Ford coil. Added to my to-do list.

NORTH-SHORE(CANADA) · #9 31-05-09, 11:48

Quote:

Originally Posted by Bruce Parker

you shut it off, it won't go .

Hi,
Is the motor turn tight ?

Bruce Parker (RIP) · #10 31-05-09, 14:20

Quote:

Originally Posted by NORTH-SHORE(CANADA)

Hi,
Is the motor turn tight ?

No, it cranks the same hot or cold. If it was getting stiff wihen hot, what does that tell you?

NORTH-SHORE(CANADA) · #11 31-05-09, 14:46

Quote:

Originally Posted by Bruce Parker

No, it cranks the same hot or cold. If it was getting stiff wihen hot, what does that tell you?

I don't know it happen with my landrover but i think it the carb that is flowding but not sure

after it hot the motor turn tight

Bruce Parker (RIP) · #12 31-05-09, 15:34

Quote:

Originally Posted by NORTH-SHORE(CANADA)

I don't know it happen with my landrover but i think it the carb that is flowding but not sure

after it hot the motor turn tight

Hmmmmm. There could be only two reasons I can come up with. Either the unburnt fuel is gumming up the cylinders and rings or the heat is expanding something. There shouldn't be any greater electrical draw with a hot motor but if the battery was running down somehow it would seem like it was getting harder to crank.

Grant Bowker · #13 31-05-09, 16:13

it might be related to the starter motor also getting hot by heat transfer. Possible problems in the starter could be either electrical efficiency changing when hot or mechanical due to clearances of bearings or other parts changing when hot.

NORTH-SHORE(CANADA) · #14 31-05-09, 16:18

Hi,
Hum starter probleme possible wy not

but would you think if my carb is floding that i have to much compression

greg anderson (RIP) · #15 31-05-09, 21:42

Hi Bruce -When I put my carrier together I installed a new resistor because the original looked a bit scruffy -but the new one didnt seem to work well so I put in the original old one and I have had no further problem (touch wood ) -Greg

Mike Timoshyk · #16 31-05-09, 23:09

What a coincidence.....I drove my Ford down to the Windsor Military Tattoo and while arriving at the site she died...did all the preliminary stuff for vapour lock. Even went so far as taking the fuel pump off and priming by hand...had fuel....mmmmm Jordan Baker happened to pop his head in and asked if I had spark. Voila....no spark. Also weak battery after a series of cranking. With the vast knowledge of Geoff Bottoms, a check was done to see if points were opening...yup....so the coil was dead. He went out and picked up a new 6 volt coil and charged up the battery. Still no spark....so down under and replaced the rotor as well....and voila...she started up. I was using an original NOS coil which sat on top and above the engine. I understand they tend to fail as they are tar filled and the new repro ones are resin filled and more trustworthey. Things to do.....carry spares of all electrical components. Will check the resistor angle as well to try to elimate any future mishaps....Geoff has an interesting story about getting to the Tattoo as well.

Cheers from Windsor

Mike Timoshyk

Bruce Parker (RIP) · #17 01-06-09, 04:02

It's got to be one of those. Whatever it is, cold: go, too hot: no go, cold again, go, every time.

Big D · #18 01-06-09, 05:06

Gidday Bruce,

I don’t know whether this will help but I had a similar problem with my Willys jeep which is on 6 volts. I’m with everyone else in thinking that it is the coil that is the cause of your problems.

My jeep used to start fine from cold but after about 30-40 minutes of useage it would just die. It would not restart unless I left the engine to cool for at least an hour. When the engine died I found that there was either no spark at the plugs or it would be an extremely weak spark.

What I did was to gradually go through the ignition system and replace a piece at a time in this order; plugs; points; rotor, condenser and then finally the coil.

What I never got around to trying was a suggestion from someone else in having a plastic bottle of water to squirt on the sides of the coil to cool it down quickly when hot, just so that we could immediately pinpoint that it was indeed the problem.

In the end I replaced the coil before trying this and the jeep hasn’t missed a beat since.

The bottle of water might be worth a go when it happens.

Cheers

Darryl

Bruce Parker (RIP) · #19 01-06-09, 05:26

Quote:

Originally Posted by Big D

Gidday Bruce,

I don’t know whether this will help but I had a similar problem with my Willys jeep which is on 6 volts. I’m with everyone else in thinking that it is the coil that is the cause of your problems.

My jeep used to start fine from cold but after about 30-40 minutes of useage it would just die. It would not restart unless I left the engine to cool for at least an hour. When the engine died I found that there was either no spark at the plugs or it would be an extremely weak spark.

What I did was to gradually go through the ignition system and replace a piece at a time in this order; plugs; points; rotor, condenser and then finally the coil.

What I never got around to trying was a suggestion from someone else in having a plastic bottle of water to squirt on the sides of the coil to cool it down quickly when hot, just so that we could immediately pinpoint that it was indeed the problem.

In the end I replaced the coil before trying this and the jeep hasn’t missed a beat since.

The bottle of water might be worth a go when it happens.

Cheers

Darryl

Thanks Darryl, what you say best describes what I've got going. I wish whatever is crapping out would just melt, or blow up so I would know what the problem is and fix it. So far, I've been trying to keep the engine compartment 'original' so I may try a new coil or, as was suggested, hide a modern 6V coil and run the wires through a dummy Ford one...for cosmetic purposes.

The water on the coil to cool it may not work. The coil IS cool. It's the resistor that causes third degree burns when I check it with my finger.

One last thing was the plugs. I ran heat range 8 plugs and had all sorts of starting problems. I changed to 10's and it made a world of difference. That's not the problem now though.

Keith Webb · #20 01-06-09, 11:21

On a F15A which had the helmet distributor. Would run OK for about 30 mins then conk out and not start until it had cooled. I changed the distributor, using an adaptor to fit a crab with a separate coil. Worked fine.

Lynn Eades · #21 01-06-09, 12:12

The resistor is supposed to get hot. Thats why it has the vented tin shield, and its wound on a ceramic core.
Like I said at the start, Change the bloody coil.
Cheers.