The following pics show how to properly set the initial timing on the Model B Ford distributor with a Pertronix Ignitor electronic ignition.
This conversion replaces the mechanical points and condenser with a solid state Hall effect transducer which switches the primary current to the coil on and off. The transducer reacts to reversals in magnetic field strength induced by cobalt magnets. The magnets are embedded in a plastic ring which attaches to the stock distributor cam.
The mounting position of the transducer on the upper plate is critical to assure triggering at the proper position of the rotor relative to the distributor body electrode throughout the range of static plate adjustment.
The transducer has an electronic latching trigger, and the dwell time is controlled by two sets of magnets. Four north pole out, and four south pole out magnets trigger the on-off dwell time. The dwell is set at 28 degrees and is not adjustable.
Regular firing is often not possible on Model B distributors with conventional mechanical points and worn shafts or bushings. The Model B distributor is known for the excessive wear and slop which develops between the main shaft and the movable upper cam shaft due to the small diameters and surface area between the two shaft pilots. This clearance and wear changes the geometry and increases (amplifies) the variation in the point arm movement and spark timing in a stock point ignition set up.
The transducer mounting is precisely located on the plate by a special fixture which was designed expressly for this purpose. The transducer should also have heat sink compound applied between it and the plate.
The transducer mounting position on the upper plate was designed so that the rotor-to-body electrode relationship remains correct, no matter what position the static upper plate is re-adjusted to after initial timing is set.
Model B upper plates are not available new but originals can be modified to properly position, orient, and mount the Ignitor transducer.
1) The pic above shows the initial timing position of the upper plate to the cast housing. The plate must be centered on the hash mark on the casting before adjusting the cam and rotor. This can be done on the bench. All the subsequent cam and rotor adjustments are made with the distributor on the engine.
2) Shown above is the Model B front timing cover. The timing pin hole is located at the top of the boss. Use the instructions below only for the Model B cover. If the hole is located at the bottom of the boss, it is a Model A front timing cover produced for service and the instructions for the Model A cover should be followed.
3) The pic above shows the initial timing position of the rotor when timed with a Model B front timing cover. The Model B timing cover is shown in Section 2, and has the timing pin hole located 19 crankshaft degrees BTDC. At that point, the center of the rotor should be centered on the electrode in the distributor body.
4) The pic above shows the Model A front timing cover. The timing pin hole is located in a round boss. When the timing pin is in the dimple in the cam gear, the crankshaft is at 'zero' degrees and the number one piston is at TDC. Use the instructions below only for timing the Model B distributor with the Model A timing cover shown above, or with the Model A 'service' timing cover with the timing pin hole at the bottom of the boss.
5) The pic above shows the initial timing position of the rotor when timed with a Model A front timing cover. The Model A timing cover is shown in Section 4) above, and has the timing pin hole located at number one piston TDC (0 crankshaft degrees). At TDC, the trailing edge of the rotor should be aligned with the number one cylinder electrode in the distributor body.