Rotor Gap

By: Wayne Mandeville

Most of us spend a lot of time tuning our Model A’s. You know the usual stuff---point gap, timing, spark plugs, and minor carburetor adjustments. But there is one thing we often do not check and it can have a significant effect on engine performance. I am talking about the rotor gap.

The first thing to do is to check the alignment of the rotor tip to the contact point on the distributor body. Take off the distributor cap and unhook the spark plug wires. If you leave the spark plug wires hooked to the distributor body they have a tendency to put tension on the body and cocking it out of alignment. The flat angled rotor tip should be horizontally straight across from the contact molded into the distributor body. It should not be higher or lower. Do not try to bend the rotor tip, as this will either cause it to break or will cause the rotor tip to not be parallel with the contact point.

One solution to fix low misalignment of the rotor is to cut some shims and place them inside of the rotor body between it and the cam screw until the rotor tip alignment with the contact points is the distributor is correct. Remember to cut a notch in the shim or shims to match the inside of the rotor body. If the rotor is to high it is best to try another rotor button or distributor body, or professionally have some metal removed from the top of the distributor cam. Once the vertical misalignment is resolved, move on to he horizontal clearance.

Often times after polishing rotor tips and contact points, many Model A’s have as much as 0.060 gap. The correct gap to make you Model A perform at maximum is 0.035 as specified by ole Henry himself. If the horizontal gap is to much you can build up the contact points with solder and then carefully file them back to the correct gap. Or once again try new or different parts. Often times the tolerances of reproduction parts vary and you can get a better adjustment if other parts are used. If you originally had any missing or sputtering, this may solve you problem. This is not guaranteed to solve ALL issues with distributors but can certainly help.

Wayne