Hard hot Start Problem (common)

[Bill OH]

Look for voltage drop in your starting circuit by connecting a voltmeter across a cable and try engaging the starter. If the meter moves up more than .05 volt, get the connections cleaned or a heavier cable. Connecting from the battery negative to the starter terminal and engaging the starter should not show more than 0.1 volt. You have disclosed that you do not have a cable from the firewall to a head bolt. You need that cable. You also need to check for voltage drop by connecting the voltmeter to the positive of the battery and to a head bolt and engage the starter. Again, the meter should read 0.1 volt or less. You have an Optima battery? Puts out very satisfactory starting capability.

 

[Brendan]

As mentioned the cable to the starter should be of 00 or 0 gauge copper, properly crimped
ends. Check that the cable is not frayed. The end crimps should not have bare wire visible, which leads to corrosion and resistance. Starter can be removed and cleaned for good ground connection. If the starter is in need of rebuild, also consider a new gear reduction style, for about the same $$ or less than a new / rebuilt stock starter.
The motors on these draw less amps and use the gear reduction to multiply the torque applied to the flywheel.
Optima battery is the way to go as well. I ditched the lead acid battery.

Had the same problem on my 49 when I first acquired it, 22 years ago.

the sound of a Flathead cranking on 6 volts is part of the experience for me

 

[Gene1949]

Because lots of people were driving old, tired cars that had maintenance problems. When all is well, no hot start problem.

And that was the key. When those cars were new they did function as designed. However, those "new parts/autos" had a relatively short working life.
IF I were to remain "period correct" and expect the drive the car I would replace everything electrical under the hood.

 

[SoCalCoupe]

Battery is grounded to the firewall and there is a second ground on the firewall to the engine head stud.

OK. Just went through lots of flathead engine compartment pictures on eBay and did what I should have done first, looked it up in the EFV8 club 41-48 Ford book.


Of course you are right.


"Three threaded studs for ground strap are swaged into the firewall. As the battery on a 6-cylinder car is on the driver's side, while the V-8 battery is on the passenger side, two studs are provided, one of which will be unused on any particular car. A third ground stud is located near the lower center of the firewall for a ground strap that will connect to the engine via a convenient head or manifold bolt."


Located both the 6-cylinder and engine ground studs. Never noticed them before. No engine ground strap. One more thing not done right by the previous owner(s). Before I even get my hands dirty messing with the starter bolts, I'll buy and install that firewall to head/manifold strap.


Not my car, but here's a picture from something on eBay. I see the engine ground strap just to the right of the starter solenoid. Looks like it's connected at a head bolt but a little blurry.

 

[ct1932ford]

Sounds like timing is advanced too much!

 

[Lawson Cox]

OK.

"Just went through lots of flathead engine compartment pictures on eBay ..."

What were you actually pulling up on eBay. I could not find anything under "engine compartment" except pictures of aftermarket electric fans, no original engine compartment pictures.

 

[SoCalCoupe]

OK.

"Just went through lots of flathead engine compartment pictures on eBay ..."

What were you actually pulling up on eBay. I could not find anything under "engine compartment" except pictures of aftermarket electric fans, no original engine compartment pictures.

Sorry, not clear. I was looking up 1941 Fords for sale hoping that one of them would have an engine compartment picture showing the engine ground strap.

 

[petehoovie]

I found this one. Don't know if it's correct or not >

And this one > Battery to firewall connection?

 

[Karl]

And that was the key. When those cars were new they did function as designed. However, those "new parts/autos" had a relatively short working life.
IF I were to remain "period correct" and expect the drive the car I would replace everything electrical under the hood.

Again not my experience -Every one I know who has had problems with reliability in their car have had it either "restored" by a shade tree mechanic and/or have upgraded it for reliabilty with mass produced modern inferior parts that Henry's quality control inspectors would have consigned to the scrap heap instantly. After 88 years and 105,000 miles my car is stil running many of the original electrical components with no problems. For me the functionality and relability of such old technology is part of the charm of owning an old vehicle -but each to their own

 

[Tim Ayers]

I made the cables for the battery, ground, and starter. I forget the place I got the cables, but it was all high quality copper wire that I crimped and soldered the ends on to. All cables came in the length I specified.

For purist, it was plastic shielded, but I slipped that black tar covering over them and you'd be hard pressed to tell they aren't original.

I'll try to find the site I got them from. Quick shipping and great price for US made copper cable.

 

[pistonbroke]

OK, we have had this topic many times but I like to here it as it means my friends are driving (or want to be) their old iron. I have had many old 6volt flatheads, Ford , Lincoln, Dodge and Cadillac. The Lincoln Zephyr and the 46 Cadillac were the ones that tested my knowledge on starter draw and cranking speed. First and foremost, you have to have the cold cranking amps. On the caddy I use two optimas in parallel just to put my wife at ease when she drives it without me around. The Optima batteries have the most cold cranking amps in the 6volt field these days and you can hide on inside the case of your ford batterie case for show. Second , Cables need to be big , the bigger the better and the finer the wire strands the better. A lot of the new cables look big but just have more insulation and less copper. Look closely as I was fooled by a on line vender myself. Wire routing is next, the positive ground cable should be attached to the engine, mine are on the head bolt/studs. The negative should go to the solenoid in as short a path as possible. The same goes for the cable from the solenoid to the starter' Next, it's the solenoid that turns on the the starter circuit . These are simple switches that can work well for thousands of starts but eventually the contacts will burn and create resistance . If your solenoid get hot when starting you should replace it(heat is resistance) with a quality one. The starter motor is the hardest working part of this system. Just because it works doesn't mean it works well . These can be tested by a good electrical shop . I have taken most of my starters apart(even the new ones) and lubed the head or nose bushing with molly bearing grease to reduce the friction as well. This does seem to make a difference. If you follow these simple steps and have good clean tight connections. You ford should start in any condition, hot or very cold. May there always be road , Tim

 

[swedishsteel]

Welding cable makes the best battery cables. It is very fine strand and the insulation remains flexible in all temps and won't crack, like battery cables you buy at the local box store. Your local welding shop usually has it bulk, or there are various online vendors as well. As stated previously the bigger the better. I use at least 1 gauge or if running a little distance 0.

 

[Flathead Fever]

Others have said it. You must verify that you have available voltage with a voltmeter. You cannot work on electrical stuff without a digital voltmeter. Otherwise, you're just guessing. If while cranking, you have the proper available cranking voltage then you have resistance somewhere in the circuit. You can't check with on ohmmeter for resistance because the meter is only using a very small amount of current to check for resistance. That works on small current circuits but not on large ones. That amount of "meter" current can easily flow through a large cable or solenoid. The parts will show no resistance. But when a large amount of current like a starter tries flowing through, it cannot. So, the way you check for this is by doing a voltage drop test. It's easy, its fast and it will find the problem if its resistance.

Forget its electrical and let's assume it has water flowing in it. If it was a very large pipe the water would come out the end with no pressure because the pipe offers no resistance. Now if the pipe had a restriction somewhere in it and you had access ports and were able to take pressure readings at different spots along the pipe when you found the restriction the water would try and flow around the restriction and out the access port and through your pressure gauge. That is exactly what is happening when you do a voltage drop test. If the area between your two-meter leads is okay, there will be no back pressure there because the cable, connection or device offers less resistance than the meter. does. When you put your leads on either side of the restriction with current flowing and there is a restriction in that spot the current will try to flow around the restriction and through the meter.

Voltage is electrical pressure. So, on a 12V system if your meter read 1.5V that means there is a 1.5V pressure drop between your two leads. Only 10.5V of pressure would be making it to your starter and it would crank slowly. That entire 12 Volts has to be accounted for. If the battery measures 12.6 volts across the posts and you put the meter leads across both ends of the positive cable and it measures .1 volt. You put the leads across both sides of the starter cable, and it reads .2 volt. You put the leads across both ends of the ground cable and it reads .1 volt. That is .4 volt drop That means that it you put the leads across the positive side and negative side of the starter you should see 12.2V. There cannot be any missing voltage. So, what if if the starter shows a 10.2V drop. Somewhere we are missing 2 volts. Let's try putting one meter lead on the positive battery post and one lead on the positive battery cable and crank the engine. The meter reads 2 volts. There it is the resistance is in the battery terminal to battery post connection. Do a voltage drop test across the starter when it's cold and when it's hot. If you want to just, try this test. Set the meter on the 12V DC scale and stick the positive lead on the batterie's positive post and the negative lead on the cable and turn on the headlights. It should read zero. Turn off the lights, remove the battery cable and just barely set it back on causing a bad connection and turn repeat the test. You will get a voltage reading on your meter, that is the drop in voltage across that bad connection. This is how electrical stiff must be tested.

Here is YouTube video showing a voltage drop test.

https://www.youtube.com/watch?v=paw80mS_Kxg

 

[SoCalCoupe]

Problem solved.

Engine ground strap arrived in the mail and I installed it today from the firewall to the intake. This part was missing when I bought the car a year ago. Hot cranking is now just as good as cold cranking. Just as good as a 12v conversion for my purposes.

Thanks to FordBarn for helping me identify the missing part.



No more fears about restarting after stopping for gas or stalling the engine with bad clutching.

 

[38 coupe]

Good news, thanks for the update.
I'm another member of the "6V works fine" group. Back in high school I started my 52 sedan on 6V when the engine was boiling over, definitely a "hot" start and no problem for the 6V system (the radiator on the other hand was terrible).