Hello, I own a '51 Ford Custom Deluxe, or Shoebox Ford. It's a stick-shift, three-on-the-tree.
The car had power issues and would die in the past. I lent my local mechanic the handbook to the car and the shop fixed it a couple of months ago. It was determined that there was a problem with the voltage regulator, and the problem was fixed. Previously, I used to use a kill-switch from the previous owner that would disengage the battery every time I shut off the car and left it in the garage. After the mechanic fixed the voltage regulator, he told me not to bother with that switch/dial any more.
The other week I replaced a headlight on the car, and the car wouldn't start and the engine wouldn't crank when I put the key in ignition. No click, nothing. The car is positively grounded and operates on a 6-volt battery. My friend and I used a power invertor and another cord/device with wires (My friend knows the names of the stuff better than I do) and used my modern car to power the '51 Ford. The Ford ran that night. A week later I returned to the garage, and once again, the car won't start and there's no clicking or engine crank when I put the key in the ignition. What can you tell me?
If it was mine, I'd convert it to 12 volt and put in an alternator.
Is the battery good? Has the generator been polarized? When the engine is running what is the voltage measured at the battery? Is the generator cutout in the voltage regulator working?
The battery was put in two or three months ago. I currently don't know enough about cars to answer your other questions.
Is it true that if I put the car in third gear and rock the car back and forth that it'll start? Does the car need to be rocked while the ignition key is turned?
What you're talking about is push-starting the car. This can be done on older cars that have manual transmission, and some with automatics. Basically if the battery is too low to work the starter you turn the engine over by pushing the car down a driveway or deserted stretch of road and putting it into gear with the ignition on. You can roll it down a hill or push it with another vehicle. (On cars with small engines like VW bugs you could get them running by jacking up a rear wheel and spinning it by hand. You won't be able to do that with a flattie V8 or even a six.) Push-starting is obviously not something you want to be doing as regular practice.
As far as the other items, typically a generator needs to be polarized whenever the battery is disconnected. Otherwise the polarity might reverse and it won't charge the battery. The cutoff relay, which is usually in the voltage regulator, prevents the battery from discharging into the generator when the car isn't running.
Since it sounds like your battery is discharging you might want to get those items checked out. Problem is there are very few mechanics around who know how to work on those old generator systems. It sounds though like you at least have one that knows how to deal with a relay-based voltage regulator.
I agree with @mittegag, really the car would work best if converted to 12 volt negative ground and an alternator installed in place of the generator. (There are even alternators designed to look like old-school generators if you're concerned about maintaining original appearance.)
Thanks so far for your answers!