1941 V8 starting issues

[displayguy]

I am still having issues restarting my 1941 Ford V8 1/2 ton while the engine is hot. The truck will start up immediately when cool and runs great. After I shut it down restarting is almost impossible. It acts like the battery is almost dead. I have replaced the battery, starter and had the coil rebuilt by the best. Still have the same problem. All electrical connections are clean and the wires are the correct gauge.
Please help!!!

 

[Lawson Cox]

Are you using 12V battery cables? Get some 00 welding cable and make up some good cables. It will work wonders.

 

[G.M.]

This sounds and acts like what I described in a post in the past day or so on this forum. Could be starter but is most likely battery cable size or connections. If you have the battery disconnect with the green knob get rid of it. 2/0 cables is what is required not the dinky cables supplyed by most parts suppliers. They supply 12 volt cables with a woven sleeve over the cable that makes them look larger but the copper is to small. These cables also have small battery ends on them. These are all resistors and drop the voltage to the starter and coil making it hard to start. Starter, cables or connections is the problem. Or a bad battery but it don't sound like that. G.M.

 

[ford1]

if your battery is good and also your starter it should start with no problems, make sure all grounds are to clean metal, run a heavy 6v cable fron the battery to a head bolt, run another from there to a starter bolt, run another from the starter bolt to the frame and to the cab, if all are installed right it should work, hot or cold, the only other thing i can think of is the exhaust pipe is run to close to the starter and over heating it

 

[Tinker]

Have you checked the connections on the ignition switch.

++++ True enough GM. I had a hard starting issue a while back, thought it was over heating. Replaced the coil, plugs, condensers, etc. Worked that battery to death trying to start it.

I had replaced the wire from the coil to the ignition switch a couple years before. When I did I didn't tighten the connection on the switch well enough that it came loose. I've broken one before by over tightening and was hesitant to put any pressure on it.+++++

 

[G.M.]

Tinker the ignition switch connections don't act like the "battery is almost dead". It would turn over good but be hard to or not start. G.M.

 

[MN47Ford]

Your problem is probably the coil and or condenser. When the truck is warm feel the coil and see if it is really hot. When the coil overheats and or gets old it wont give enough charge to restart the truck. That is why when it cools down the coil is more efficient again and the truck can start.

 

[41ford1]

Your description sounds like a heat related problem in the starter circuit. You stated: New battery, correct size wires and replaced the starter. If the starter was not new or rebuilt I would check the bearings. If they are worn it will cause the armature to drag on the fields. This first shows up when hot. It will turn over slow. The solenoid may have high resistance in heat also causing slow cranking. Try jumping around it when hot.

 

[Flathead Fever]

Usually a heat related cranking problem will be caused by a faulty starter. Before you condemn the starter you should rule out all the other components.

A professional automotive repair shop performs a voltage drop test to find the component that is causing the voltage loss rather than replacing perfectly good parts hoping to solve the problem. This is especially useful on large current circuits such as starters. Before you perform this test you need to understand what it is you are doing.
　
It is very important that you learn the relationship between voltage, amperage and resistance. This is what usually separates the home builder from the professional mechanic. It is not difficult to learn, and you only need to learn the very basics to work on your old Ford’s electrical systems. For some reason most automotive enthusiasts minds shut down when they here words like voltage, amps and ohms but if they were working on the water lines to their houses they would not have any problem understanding the terms pressure, gallons, and blocked pipes. It is exactly the same. Don’t let it freak you out!

Voltage is often referred to as the pressure that is pushing the current through the circuit, just like the pressure in your water pipe determines how much water flows out of your hose. The more pressure in the pipe the more water that runs out The same principle with voltage, more voltage means more current flow. Voltage is not an actual pressure like pounds per square inch, its some magical force that causes electrons to move, for now that is all you need to know.

When we check the battery voltage, all we are doing is checking to see how much pressure is available in the battery. If we were testing the pressure in a water line we would be comparing the pressure inside the pipe to the atmospheric pressure on the out side of the pipe. We cannot test pressure by sticking the gauge completely inside the pipe because the pressure on the outside of the gauge would be the same as the pressure on the inside of it and the gauge would read zero. It’s kind of the same thing with a volt meter, there has to be a difference in voltage between the two leads in order to get a reading. One post of the battery has six volts and the other has Zero. The meter looks at both posts and tells you what the difference in voltage is between them. This feature is going to come in really handy diagnosing our starter circuit.
　
Current or Amperes, is a measurement of how many electrons are flowing through the circuit past a given point, just like gallons per minute is a measurement of how much water is flowing. I have never seen an electron but I have felt them on occation. I just have to except the fact that they are there and applying voltage or pressure to them makes them move and do work. The more electron workers moving the more potential work that gets done. If you want more work to get done you need to put more pressure on your electron workers, If you want to slow them down install give them some resistance.

Resistance is measured in Ohms and is named after some old dead guy that was smarter than the rest of us. Resistance is anything that will cause a drop in pressure. Resistance acts like a valve in your water line cutting down the flow. A Larger ohm resistor or unwanted resistance closes the valve and cuts down on the flow of electrons. Examples of resistance are: too small of a cable which does not let enough electrons go to the work site, which in our case is the starter. A bad connection that is too wide for the little electrons to jump across. Any electrical component that is not a wire, ground or switch will have resistance built into it. We need to find any unwanted resistance in the circuit, and we do that with a voltage drop test.

Every mechanic needs to learn Ohm’s law. The symbol for voltage is the letter “E”. Amperage is the letter “I” and Resistance is the letter “R”. If you have two of the values you can find the third. Cover up the letter you want to find, insert the other two values and do the math.

“E” or Voltage
_____________________________​

“I” or Amperage X “R” Resistance​

Example: if we stick a 2 ohm resistor in our flathead ignition circuit it will cut down the current in the coil and points to make them last longer. They would burn out really quick without the resistance in the circuit. Example: 6 volts divided by 2 ohms equals 3 amps, which is a small current draw. Lets use a starter circuit, 6 volts divided by 300 amps equals .02 ohms of resistance. That is virtually no resistance, barely measurable with a meter.

Normally you would never need Ohm’s Law but were going to use it to prove an important feature about the effects of resistance. The .02 or 2/100 of an ohm in our starter circuit is virtually nothing compared to the small ignition resistor, yet it makes a huge difference on a high amperage circuit such as a starter. Watch what happens if we double that microscopic amount of resistance in our starter circuit. 6 volts divided by .04 ohms equals 150 amps. Wow, that little microscopic increase in resistance cut our current flow in half. Now only half the electrons are available to do the work. That is why it is so important to use large cables on the starting circuit and make sure that all the connections are clean and tight and there are no voltage drops present.

How are we going to find that microscopic .04 ohms of resistance that is causing the problem? We don’t measure the resistance, we look for the presence of it by doing what is known as a “Voltage Drop Test.” To perform this test, the circuit needs to be activated so that the electrons are flowing. Everywhere that there is resistance in the circuit it will show up as a voltage drop because there is a difference in pressure on both sides of the resistance. Since we are only dealing with 6 volts it becomes even more critical to eliminate all of the voltage drops in a circuit.

Starting at the battery connection, place the red lead in the center of the positive post and the negative lead on the cable end. Have somebody crank the engine while you watch the meter. A good connection should have less than .1 of a volt drop on the meter. Next hook the positive lead to the battery end of the cable and the negative lead to the other end of the same cable and crank the engine again. The cable should not have more then .2 of a voltage drop across it, If the voltage drop reads more than .2 of a volt the cable is too small, has a bad crimped end or an internal problem. Somewhere there is resistance in that cable. Check every cable, battery post connection and ground. Next check the starter solenoid. On a negative ground system hook the positive lead to the side of the solenoid going to the starter and the negative lead to the battery cable side of the solenoid. Crank the engine, the meter should not read more than .5 of a volt. Your reading the resistance across the contacts in the solenoid. Last, check the voltage drop across the starter. On a positive ground system hook the negative wire to the starter terminal and the positive wire to the engine block. Crank the engine, there should be a large voltage drop almost equal to the battery voltage, if not, you could have a faulty starter. All of your voltage drop readings should add up to the available battery voltage. If your missing some voltage you still have resistance some place in the circuit.



I took some photos of a voltage drop test being performed on a battery terminal end. The first photo shows the positive lead in the center of the post and the negative lead hooked to the cable. I turned on the headlights causing the electrons to start moving. The meter reads zero because the pressure is the same on both side of the connection, there is no measurable resistance. Next I loosened the cable and stuck it back on. Now the loose connection is causing resistance in the circuit and the meter is giving us a .02 volt reading, showing us the difference in pressure between the two sides of the connection. Finally I removed the cable completely and the meter shows a pressure reading difference equal to the battery voltage.

I worked with a guy that had been a Ford dealership mechanic. He told me a story about a brand new car that had come back several times for an intermittent no start problem. It was to the point that if it was not repaired it would fall under California’s lemon law and the customer would be refunded his money. The starter, battery, solenoid, ignition switch, starter neutral safety switch and computer had been replaced. The problem was finally found by doing a voltage drop test. When the battery cable was made they did not strip the insulation off the cable before the end was crimped on. Sometimes it made contact and sometimes it didn’t. It was a perfect looking brand new cable, why would you suspect it. Never assume anything!

A little info about six volt starting systems. Electrical power is measured in watts. A one-horsepower electric motor is equal to 746 watts of power. To find watts multiply the voltage times the amperage. Lets say a 12 volt starter draws 250 amps. 250-amps X 12-volts equals 3000 watts. If it takes 3000 watts of power or approximately 4 horsepower to spin an engine on 12 volts. It is going to take the same watts or horsepower to spin that same engine on 6 volts. That means the amperage has to double to 500 amps (6 X 500=3000) to accomplish the same amount of work. That is why the cables need to be larger on your 6 volt system, they are carrying twice the amperage of a 12 volt system.

Jerry

 

[G.M.]

Jerry the 3 pictures of the battery you posted are a good example of potential problems. The terminal connector with the 2 screws clamping the cable to the connector is another possible place for a voltage drop and I doubt if the 2/0 cable would fit in plus it looks like the battery post is recessed down in the connector not giving the full surface area required for a good connection on 6 volts. You show a 12 volt battery and we were talking 6 plus the meter shows the battery voltage as being low for a fully charged 12 volt battery. G.M.