The "distributor upper plate with modern points and condenser" is in use by many Model A owners. A basic design and construction fault has been discovered. Tests on both cars and a distributor stand were made on ten different units from five suppliers.

The problems were initially revealed during timing tests of four cars at two 'A' Meets. The Ignition Timing Kit described in the Jan/Feb 1992 MODEL A TRADER, pgs 2-3, uncovered the faults and causes of the malperformance.

The specific ignition performance symptom observed was:

• The spark control full range could not be used and
• The engine stopped when the control was moved beyond some setting

The owners thought the problem was just mislocation of the timing gear dimple, piston # 1 Top Dead Center.

The malfunction was instead found to be improper location of the point assembly on the movable distributor plate. The rubbing/ actuator block was thus changed with respect to the cam-rotor slot.

The relation between the rotor extended brass conductor and distributor fixed button conductor was consequently not proper at the extremes of the movable plate rotation. At some extreme (full advance or retard), the two conductors were so separated that the spark could not jump the large air gap. The spark failed - the engine catastrophically stopped!

The above observations were strikingly visible using the cut-out cap, timing light, and procedures referenced in the Ignition Timing Kit described in the Jan/Feb 1992 MODEL A TRADER article.

The original Ford point plate, points, cam, rotor, and distributor were properly designed to work on the distributor 20° advance-retard plate rotation. The distributor button is a nominal 5 degree width additionally. The movable point arm rubbing block was positioned, relative to the rotor slot on the cam, so that a portion of the rotor conductor was always opposite the distributor button throughout the advance to retard extremes. This provides the smallest spark air gap. Figure 1A shows the proper conductor relations.

Supplier chosen "modern point assembly" does not duplicate the pivot and contact points relation of the Ford original design. This is not a prime requirement but it does also affect the point dwell time (the time the points are closed). The fabricators have chosen to use some existing holes in the standard point plate, presumably for ease of modification.

The existing plate hole chosen for the assembly pivot location changed the rubbing block position so that the cam slot improperly locates the rotor brass conductor relative to the cam high point for point opening and subsequent spark.

On some assemblies tested, this caused the rotor-distributor contacts to be separated by as much as 3/8 to 1/2 inch in the full retard position (Figure 1B). The spark could not always jump this large air gap. The engine then stopped!

There were other aspects to these "modern point assemblies." The plate hole chosen for the point pivot was unmodified or drastically modified. The point assembly consequently was not flat on the plate or had no fixed position on the plate. The assembly mounting/ hold-down screws also were involved in the point opening adjustment so adjustment was very difficult.

One possible "fix" was drilling the pivot point hole for clearance and adding a chamfer to both positively locate the pivot and allow the point assembly to be flat on the movable plate. It also separated the opening adjustment from the screw hold down functions. On plates which were drastically modified, neither of the above changes were possible.

A point plate modification and assembly that attempted to solve some of the foregoing observations was described in an article by Paul N. Sund, Pacific Grove, CA, in The Restorer - March/April 1990, pgs 19-21.

Visual examination of one of these units appeared to be a proper alteration. It was not tested on the Test Stand shown in Figure 3 or on a car.

A simple "fix" for those owners who have already installed a "modern plate" and want to make a simple and inexpensive correction is shown in Figure 2.

It consists of an extension to the rotor brass conductor. This extended tip is installed on the rotor and can be located for either retard or advance correction. Installation consists of drilling a hole in the rotor contact and bolting the extender in place.

To determine the need and extender position:

1) Temporarily replace the distributor cap with the cut-out of the Timing Kit
2) Idle the engine
3) Advance and retard the spark timing-full ranges
4) Observe the relation between the rotor tip and fixed distributor button

The extender should be mounted on the rotor so there is always overlap of the conductors throughout the full range of advance and retard spark control.

Many tests were made on "original standard point plates", "modern point plates", and distributor cams using the Test Stand of Figure 3.

The findings of those tests are to be published in several forthcoming MODEL A TRADER articles. The tests included performance as a function of point opening, spark timing, cam dwell time, production cams, and rotor contact-distributor contact relations.

The Rotor Tip Extender and Timing Crankshaft Degree Kit were designed for and are being produced by Nu-Rex, Box 9332, Akron, OH 44305. The items will be available from leading Model A parts suppliers. For additional information, call (216) 784-5334 between 4 P.M. and 10 P.M.

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