Starter System Issues

Until the 1950s, lead-acid battery technology hadn't progressed to the point that it was possible to manufacture a 12-volt battery small enough to fit in a passenger car. So until then, 6 volts was the standard for cars, and 12 volts for trucks. To provide a given amount of wattage for the starter motor to crank the engine, a 6-volt system must deliver twice the current to the starter motor that is needed in a 12-volt system. (Ohm's Law cannot be broken: watts = volts x amps.) In reality, this means that even with a well-tuned car, starting is harder in an old car than a newer one with a 12-volt system. The problem becomes worse when it's cold. Battery output drops, even while the engine turns over with greater difficulty because lubricating oil is congealed.

Some old-car owners throw up their hands in dismay and convert to a 12-volt system. I prefer to keep the car as authentic as possible, which means delivering every available milliwatt of energy from the battery to the starter motor. To do that, we must take every possible step to eliminate resistance in the electrical path between the battery and the starter motor. Based on what I've learned from an article by Walt Mordenti in the May/June 2000 issue of White Triangle News, the official publication of the Hudson-Essex-Terraplane Club, and a chapter in the very useful book, How to Maintain & Enjoy Your Collector Car by Josh B. Malks, I have taken the following measures on my 1929 Hudson, and recommend the same for any old-car owner with 6-volt systems.

• Replace the battery cable that runs from the battery to the starter motor switch. Don't use battery cables from the local Pep Boys. They're all intended for 12-volt systems. Even the largest will not handle the high current needed in a 6-volt starter system. #1 electrical cable, the largest available for 12-volt systems, has a maximum rated amperage capacity (ampacity) of 150 amps. #2/0 is rated for 265 amps. I used 2/0 stranded cable, which is as thick as your thumb. Ideally, find a welding shop and buy 2/0 welder's cable. It has hair-thin individual strands and is as flexible as rope, which makes it easy to route. The insulation is highly resistive to gasoline, grease, and solvents that can attack wire insulation. Use heavy-duty connectors, also available at the welding supply store. If possible, have the store crimp the lugs onto the cable with a special crimping tool. Don't solder the joint; that will actually increase resistance, according to electrical engineers I have consulted. A tight crimp joint is better. Cover as much as possible of the lug with elecrical tape or heat-shrink tube, so you won't accidentally short the battery to ground with a wrench while you're working near the starter motor.
• Run a second 2/0 cable from the negative terminal of the battery to a mounting bolt on the engine block near the starter motor. The car originally relied on the metal frame as a "ground return" path for the starter motor current. That works fine with a new car, but decades of accumulated rust, dirt, and grease can build up the ohms at metal joints along the electrical path. Remember, the goal here is zero resistance. On Super Six Hudsons, the battery sits under the driver's seat, a long way from the starter motor. I measured 0.4 ohms resistance on the original ground-return path, using a digital voltmeter. That was cutting starter motor current by 15 amps. (Another way to think of it is that the ground-path resistance was converting some electrical energy to useless heat rather than into useful mechanical energy.) You can run a second ground cable from the negative battery terminal to the original ground point on the frame adjacent to the battery.
• Install an Optima 6-volt battery. This is a radical battery design developed by the Gates Tire and Rubber Company in the '70s. It's now sold through Interstate Battery dealers. The Optima battery is smaller than a conventional battery, but packs a lot more starting power -- 850 Cold Crank Amps, substantially more than other 6-volt batteries can deliver. The only downside to the Optima is that if you ever let it drain completely dead, it is impossible to recharge using conventional chargers. You'll need to take it back to the dealer, who should have the heavy-duty charging equipment needed to reinvigorate a totally dead Optima. You may want to build a wooden "battery holder" to keep it from rattling around. The photo shows Paul O'Neil's design.
• Rebuild the starter switch. On the Hudson Super Six, the starter switch consists of a metal shaft that is pulled backwards when you press the starter motor foot switch. The shaft is pulled backwards until it bridges two electrical contacts and delivers power to the starter motor. In cross section, it looks like (o), with the o being the shaft and the () the contacts. Disassemble the switch, clean all contacts shiny-bright, and re-assemble. This was worth another 1.5 ohms for me, or 40 amps of cranking current.
• Rebuild the starter motor if needed. Don't try this at home. Take the starter motor to a good auto electrical shop and have them rebuild it. Walt Mordenti's article says, "Remove the starter and check for end play. Hold the starter so that the bendix is on the bottom, then lay it down and push the shaft that comes through on the bendix end, and if it moves back more than 1/32", then the starter needs to be rebuilt. The commutator must be turned, new bushing at both ends, new brushes, and most impoartant of all, the correct thickness fiber washer at the commutator end. This is not a job that you can do at home, as you need the correct tools to cut the commutator."
• Use a 6-volt trickle charger to make sure the battery is fully "topped off" to deliver maximum starting effort when the car is cold. Interstate Battery sells a very nice "smart charger" that automatically reduces its output when the battery is fully charged.
• Lastly, and perhaps most obviously, follow the manufacturer's instructions for starting procedure. Old cars don't have automatic chokes. Pull the choke all the way out for starting, even if the car is warm. Use the spark retard adjuster. (Experience will quickly show you what setting works best.) Use the carburetor heat mechanism. And, of course, make sure your engine is in good running order. If you have compression loss, fouled plugs, or anything else that degrades engine performance, it will degrade starting capability.

With these fixes to your starter system, you should be able to start your old car without difficulty, even on cold days.