Classic GM Alternator Restoration

Classic GM Alternator Restoration

Give your dirty, rusty alternator a fresh, new look

The alternator in your car is often the Rodney Dangerfield of the engine compartment. While we spend untold hours detailing the carburetor, air cleaner, manifolds, wiring etc., we generally just wait for the alternator to go bad so we can get a clean rebuilt unit and let the old one be an exchange as a core unit. However, if you're trying to keep your car numbers matching or just want a perfect, restored alternator ... paint it! The idea of taking apart that little electric dynamo is a daunting proposition, but it's actually not that hard. And by dismantling it, you'll get a better, detailed finish-plus you can do any tune-up work that may be needed while you've got it apart.


Here's our decrepit GM 10DN 12-volt alternator circa early '60s. GM dumped their old generator system in favor of an alternating one in 1963 (for the most part). The little 10DN alternator was much more compact than the old generator and used a small regulator that mounted to the firewall or one of the fenderwells. The 10DN put out a modest maximum voltage that eventually was around 61 amps. By 1969 GM introduced the 10SI Delcotron with its internal regulator on the Corvette and started offering it as an option on certain models. Within a few years the 10SI was standard equipment on all GM cars and trucks and it too would eventually evolve into newer models. As you can see, ours needed a major facelift and, because it was an early model with low numbers, we didn't want to lose it.


Pulling this alternator apart is really quite easy. The front pulley and fan need to come off first. The nut that holds the pulley to the rotor is often too tight to get off by hand. If this is the case, you'll need an impact gun to loosen it up. If you don't have an impact, take the alternator down to your local auto repair or tire shop. They should be able to do it for you. Next, there are four long bolts on the outside of the case that hold the two halves together. Remove these bolts and the two halves will separate. Now it's time to clean it all up prior to paint.


While you've got the alternator apart you can do a check up to see how the internal parts are wearing. If the alternator was not charging prior you may need a new set of brushes. Worn bearings that the rotor rides in will cause noise and eventual failure. These items can often be purchased at larger auto parts stores for replacement at reasonable cost. Inspection of the stator ring can reveal burned, broken or rusted wiring. We used a piece of scouring pad to clean the rust from the inside of the ring. As the rotor spins within the stator ring the resultant electricity is transferred through the rotor's shaft where the two carbon brushes ride at the end. The brushes will have considerable wear over time so pay close inspection to them as well.


With a clean bill of health and a thorough blasting in the bead blaster (bearings and electrical innards removed!), we prepped the case for paint with a quick dousing of wax and grease remover. Allow it to dry thoroughly and let stand in the sun for a few minutes if possible. The evaporation of the solvents on the surface of the metal will reduce its temperature greatly, and that does not promote good adhesion for the paint. We used a cast-aluminum-look spray paint to give the case a freshly cast look. Be careful to not overdo it. Excessive coats will only cause drips and sags. Two to three even coats are all you need.

Pulley & Fan

From the factory, the pulley and fan came in different colors over the years. We opted to use a bronze carb renew paint to give our fan a bright-gold cad-plating finish. The pulley itself was treated with silver zinc paint. Again, heavy metallic paint requires just two or three light, even coats to get a real, plated finish. We gave the bolts a quick blast of the silver zinc while the pulley bolt was painted cast-iron gray. Let the new paint cure overnight before you reassemble as the soft paint can't be smudged. The hardest part will be getting the pulley bolt on again without marring up the paint too badly. A couple of brush strokes with a capful of paint will do the trick if you scratch it up.

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