12v battery on 6v system?

[Crankster]

As mentioned cheap generic or "universal" battery cables are no good for 12 volt systems, and they are completely unsuitable for 6 volt systems. Be sure to check for this. Very common error. Good quality cables of sufficient gauge are critical.

Collector cars too, are often not driven frequently enough to keep the battery itself fully charged and "exercised". They will quickly sulfate and lose capacity, even if the open circuit voltage seems OK. This interferes with the ability to take a charge, and "fools" a regulator into thinking a battery is charged up as well.

The charging system itself has to be within spec in terms of both voltage and current, generators were always bit of a close run thing even when everything is straight, introduce even very small amounts of corrosion or resistance in the cables, grounds, and connections and they will be unable provide enough current to re-charge the battery in a timely manner.

A generator regulator has a charging voltage set point that is on average significantly higher than an alternator charging system. A few tenths of a volt difference doesn't sound like much, but looms large in a low voltage, high current system.

[corvette8n]

Enough can’t be said about the cables and connections. Even though they look ok, I would remove every connection and clean them until they are bright. I replaced my ground with a nice heavy military surplus braided flat cable. I then went to Tractor supply and bought a 6 volt tractor cable for the negative. You may want to look into replacing your solenoid. After all the connections are clean, tight and bright see how it starts. When done I coat all my connections with Fluid Film.
My Ford 8n would start within a half of crank even when sitting all winter. My ‘41 starts after a couple of revolutions. I do have a 6v electric pump mounted before the mechanical fuel pump for priming only. My distributor and carburetor were rebuilt by CharlieNY and my coil was rebuilt by Skip. When everything is up to snuff(as my Dad would say) there is no reason it shouldn’t start quickly.

[tubman]

Also, check your starter. I was never really satisfied with the speed with which my '51 turned over, though it never failed to start. I finally replaced the starter and it made a world of difference. Upon disassembling the original starter, I found a "cold solder" joint to one of the brush assemblies.

6 volts used to start these things when it was 20 below in Minnesota in the fifties.

[RalphG]

Just an example of how my 39 cranks in this video shot at +12F. All stock equipment here and it had one stuck exhaust valve as you will hear starting at the 1:00 mark. The battery is a bit bigger than a normal car battery but it was far from new.
This one has always had what I considered a good fast cranking speed for a six volt system. https://youtu.be/KgjsQRg7ArU

[Roger W Gerow]

Another suggestion. Most people have petroleum jelly around. The best there is to coat all the connections including the battery terminals.

[rayro39]

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Ralph G: Mine is about 1/2 that crank speed. Half loud. 2 or 3 turns. Battery was rebuilt. New battery.

Thanks for the input guys. Looking for a thicker starter to solenoid cable. This one is standard size 3/8. hopefully that's it. (plus cleaning all the contacts)