Distributor Base

The distributor of my engine is another piece which will be somewhat modified from the original plans, which call for a mechanical set of points. I have elected instead to go with a hall-effect, transistorized ignition and shop-made ignition coil. For those not familiar with hall-effect, allow me to explain:

A hall-effect IC is a tiny chip which is influenced by a magnet. It is wired into a transistor amplifier circuit, with the whole circuit then acting as an electronic breaker. When the South pole of a magnet is exposed to the end of the chip, the "breaker" contacts are closed, and the coil is being energized. When the magnet is removed, it is the same as if the breakers are opened, and the coil then fires with the distributor rotor passing the spark to the appropriate plug. A vane of any ferrous material can be interposed between the magnet and the Hall IC, with slots in the material corresponding to dwell.

 

This bevel gear was bored to 3/16" (.1875"), and is driven off the mating bevel from the crankshaft, reduced in speed 1:2. The shaft which carries this gear (and drives the distributor components) is keyed with a 1/16" key. Since a 1/16" keyway broach won't fit this bore, I had to grind a "shaper" bit which I used to shape a keyway slot in the gear. The gear is held in a small 3-jaw, the spindle locked, and the carriage inserted and withdrawn with the cross-slide progressively fed into the gear.

The tool is withdrawn after a .003" feed. You can see the curl of brass which the "shaper" tool has removed from the bore of the gear. I have used a similar technique in other cases to create internal shapes in bores using just a lathe.
The Distributor base begins life as a 2.5" 6061 aluminum round. The base section is turned to the major diameter between hold-down bolt holes....
...and the stub base is turned into the aluminum.
Initial countouring is done in a collet block in the mill. Final shape (shown below) is achieved with a rotary table by taking a series of tangent cuts, and blending with a file and fine silicon carbide paper.
The finished base now equipped with a timing advance arm. The small white IC chip is a mounted hall-effect IC. Above it is a receptacle for a tiny neodymium magnet. This pair form the "breaker" contacts for the ignition system. The base is slotted at the right for a small advance/retard lever which will project below the base. Still to be mounted is a ferrous timing vane and rotor carrier.

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