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Electrical - Engine Components

By Jeff Zurschmeide


Your carís electrical system takes in a wide variety of parts and components. Everything from the starter motor to your ignition the light over the license plate to the cigarette lighter comes under the general heading of electrical parts.

This article focuses on the big, heavy components that generate and use electricity specifically to keep your carís engine running, and on the special components of your ignition system. These include the generator (ďdynamoĒ is another term used in many older cars) or alternator, voltage regulator, and starter motor.

When you took your engine in to be checked and probably rebuilt, either you or the engine shop removed your engine electrical components. Your first step is usually to test these components, and that process is different based on whether the components are on the car or removed.

If your components are already off the car, take them to a reliable automotive electrical shop for testing. These tests are more conclusive than tests you can perform, and can often reveal weakness or intermittent failure problems. Some general-purpose automotive shops and parts stores can also test these components for you.

If the components are still on the car, you want to ensure a fair test. A bad battery, unknown drains on electrical power, or increased resistance in the wiring can all affect a component test, so make sure youíre using a fresh battery and if possible, all new wiring to perform these tests. You donít have to rip out the old stuff, just hook up new wires for the purposes of the test.

HINT Hint...
Make an investment in a battery and generator tester. A battery tester has two big clips similar to those used on jumper cables. If you hook it to a battery and turn it on, the gauge tells you how many volts the battery can deliver under load. A weak battery will start out delivering 12 or more volts, but quickly drop below 10 volts.

Battery tester
Battery and Alternator Tester

You can also use the same box to test a generator or alternator by connecting the clips to the positive and negative poles on the generator or alternator and reading the output. For a 12-volt system, a healthy generator or alternator should read between 13 and 14 volts. A 6-volt system should read up to about 7.5 volts.

To test a starter motor, connect a battery up with new cables and then use a remote starter trigger (you can buy them at any auto parts store) to test whether the starter has enough torque to spin the engine under load. Testing a generator is a little more tricky. The engine has to be running to test the generator fully installed. Use your charging system tester or a good volt meter.

HINT Hint...
One way to perform a basic test an alternator in the field is to take a steel screwdriver and hold it just in front of the central rotating shaft. This is the armature shaft, and as it spins, the magnets in the body of the alternator create a magnetic field in the armature wire windings. You can feel this field by holding the screwdriver about 1/4-inch from the end of the shaft. The screwdriver tip will be attracted to the shaft. If the shaft does not magnetize, then chances are your alternator isnít working correctly.

Many older cars that use generators also feature a separate voltage regulator. Alternators generally have an internal regulator. External voltage regulators are the most difficult component to diagnose yourself. The danger with a faulty voltage regulator is that a bad regulator can kill your generator, so the two components are best tested professionally and as a unit. If either component is bad, rebuild or replace both of them.

Starter diagram
1940s Delco Starter

Older generators and starter motors can often be rebuilt by the home restorer. Typically, the restoration process includes replacing the bushings and bearings that hold the armature that spins within the component housing, and also the brushes that make contact with the armature. Replacing those parts, together with a thorough cleaning and inspection, can often refresh an older generator or starter to as-new condition. Put on a new coat of paint and the component is ready for further service.

Generator diagram
1940s Delco Generator

Newer components such as alternators are not designed to be serviced by the consumer, however, and so with those you must pursue a replacement strategy. Luckily, these are also more likely to be available in new or professionally rebuilt condition.

Your best bet for purchasing new or rebuilt components is to locate an automotive electrical specialty shop in your area. They can order many vintage parts that are no longer available through conventional parts stores.

Dos and Don'ts
Thumb up  DO
  • Have each component tested to determine if itís working at its rated capacity
  • Have each component cleaned and restored by an expert
  • Pay special attention to corrosion on connections

Thumb down  DON’T
  • Donít assume that a component is OK because it seems to be working
  • Donít rely on used parts to work reliably
  • Donít simply paint over an old component as a restoration
The Popular Restorations Project Car
Author photo

1946 Packard: Rebuilding the generator and starter

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When I started restoring the Popular Restorations project car I had every intention of rebuilding the generator and starter myself. I even purchased the rebuild kits from Kanter Auto Products and disassembled the generator. But then I got to thinking about it. To do it right the commutator (the cylinder of copper blocks on the armature) should be turned. That is, it should be machined down so itís smooth, even, and shiny. Also, I wasnít sure whether to undercut the mica between the commutator blocks--I know in some cases you are not supposed to undercut but I couldnít remember which cases. While looking on the web for my answer I read an article that recommended checking the tension for the brush springs. In my youth I wouldnít have worried about these minor details; but for the Packard restoration I wanted everything to be as close to new as possible. So I decided to let a professional do it. I put the pieces in a box and delivered it to PMX (see the interview on this page).

The rebuilds were not that expensive and now that itís done I feel more confident in my electrical system than if I had rebuilt the starter and generator myself. The starter cranks the engine over at a good speed, especially for a six volt system. Someone in my Packard club said that if everything is in proper working order there is no reason a 6 volt system should crank slowly. So far I agree!

The only drawback to a perfectly functioning 6 volt system is that you canít power 12 volt devices--at least not those that draw many amps. Aftermarket voltage converters (6V to 12V) are available on eBay, but they typically put out two or three amps. Iím planning on installing a music system, one that is easily removable when the car needs to look correct. I suppose Iíll have to put a 12 volt battery in the trunk and just recharge each time I park at home.

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Comments
Interview
 

PMX Alternators & Starters

By Jeff Zurschmeide

Bill Jungck, Owner
8420 SE Hinkley Ave.
Happy Valley, OR 97086-3616
Phone: (503) 777-7172

PR: If someone is restoring a classic car, what would you advise them to do with their charging system and starter?

PMX: With an older car, itís usually a generator, rather than an alternator. If the carís been sitting for a while, itís good to get the generator and starter cleaned up and rebuilt to get the gum and spiders and birdís nests out of them. This is just to get things working the way theyíre supposed to.

PR: What about Voltage Regulators?

PMX: The job of the regulator is to monitor the voltage and keep it up around 14 volts.

PR: Can a bad regulator destroy a generator?

PMX: That depends on how the regulator fails. If the regulator doesnít control the generator, it can overcharge and burn out the armature. But if it fails and doesnít charge, then the battery goes dead, but you havenít damaged the generator.

PR: Can someone test a generator at home?

PMX: You need to have something that will test for six volts, if itís an older car. The battery should show about 6.2 volts, or 12.6 volts on a 12-volt battery. Then if you fire up the car it should go up 1-2 volts if itís charging. For a 6-volt system, you want to see 7.2 to 7.5, and a 12-volt system should show about 14 to 14.5 volts. Then I usually have people turn on the heater and the headlights and rev the engine a bit, and you see a drop down to about 13 volts at the battery. But you have to have 13 volts to be sure youíre not running off the battery.

PR: If the charging system is not working, what do you do?

PMX: In most cases, I rebuild your components. I test both the regulator and generator and test them both, then rebuild from there.

PR: How about starter motors - what do you do there?

PMX: I rebuild a lot of them. Some of them Iíll convert from 6-volt to 12-volt operation, if people are updating their cars. Iíll go through the starter and put in new brushes and bushings and clean everything up. Sometimes we replace the solenoid or the bendix gear. One important thing is that if they stay with a 6-volt system, I make sure itís got a 6-volt cable, because those have to be about twice as big as a 12-volt cable to run the starter correctly.

PR: Any other good advice?

PMX: Keep your battery charged up. Try not to jump a car with a flat battery and then use your charging system to charge up the battery. Itís better to use a battery charger to do that, and itís hard on your alternator or generator. And one more thing, make sure youíve got good grounds, especially from the engine block to the chassis. A lot of times those will get disconnected and then youíve got a ground path that runs through the throttle cable or something. So, make sure those grounds are in place.

Recommendations
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Jim Horner
Automotive Electrical Handbook
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Tracy Martin
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Associated Equipment
Associated Equipment 6031 Battery Alternator Tester

This tester is capable of battery load testing (125 AMP) and will also perform a charging voltage test, a starter motor test, an alternator test, and a GM diode trio test.


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Schumacher SC-600A SpeedCharge High Frequency Battery Charger
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External Links
SecondChanceGarage.com has a good article on Automotive Electrical Systems.
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