Distributor Gears
Marvin gently drives the gear in place, using bronze for this application. He will measure clearances before permanently installing the gear and shear pin.
Because we have to deal with both hydraulic and mechanical roller camshafts in today's world, we have to think differently about distributor gears. Flat-tappet cams, like those used in vintage 289s, do fine with cast-iron distributor gears because the cams are also made of cast iron. This means neither metal is harder than the other. However, roller camshafts, such as those found in late-model 5.0 engines, are made from hardened steel, mandating the use of either a bronze or steel distributor gear. A cast-iron gear with a steel camshaft will not live long.
Bronze gears have a limited life span and are typically used in race engines. Steel is the gear of choice when you're operating a roller tappet camshaft on the street. So if you're planning to drop your vintage distributor into a 5.0-style block with the roller cam, be sure to replace the cast-iron gear with a steel version, available from Ford Racing and most cam manufacturers.
With the cam button already installed, the breaker plate is dropped in place along with the vacuum advance, and checked for proper operation. Because Marvin still has tuning to perform on the mechanical advance, he hasn't made anything permanent yet. | 
The dimension between the housing and the gear is checked. This measurement should be 4.031-4.038 inches from the bottom of the mounting flange to the bottom of the gear for all 289/302 distributors. | 
Once Marvin has ascertained proper gear positioning, he drills a fresh shear-pin hole for permanent positioning 10 degrees from the original position. |
Installation of the PerTronix Ignitor II begins with this shutter wheel, which fits over the cam as shown. Adhesive isn't required. | 
Marvin installs the PerTronix Ignitor II and sets the air gap. PerTronix provides the plastic thickness gauge to properly set the air gap. | 
PerTronix wires are fed through the distributor housing via the rubber seal. The red lead goes to the positive side of the ignition coil, the black to the negative side. The red lead provides power, while the black lead controls the cycling of the coil. |
Marvin uses a good old-fashioned distributor machine to dial in spark curve. He does this by using the right combination of weights and spring tension in the mechanical advance. | | |