A New Distributor Upper Plate Assembly
At Long Last! Modern Points, Modern Condenser, and the Correct Geometry
Points, condenser failure, and their maintenance are major problems with reproduction Model "A" ignition systems. Rubbing block wear and failure is caused by inferior material or an improper distributor cam. Condenser failure is caused by poor construction and heat damage due to proximity to the hot engine head.
An unknown "A" owner recognized these problems and made a correction by mounting modern points and condenser on a stripped and modified standard upper plate. Stripped standard plates, so modified, have been made and sold by many sources since then.
A Model A Trader article1 reported on tests of ten different units from five suppliers. It noted faults as:
- The plate hole chosen for the point pivot changed the rubbing block-cam high point relations so the rotor-distributor contacts were improper and air gap separated at some advance/ retard spark position.
- The point assembly had no fixed position on the plate and moved about.
- Hold down screws were involved in the point gap adjustment so setting was difficult.
The foregoing problems caused specific ignition failures as:
- The spark control advance/retard full range could not be used
- The engine stopped when the control was moved beyond some setting due to the air gap between the rotor and distributor contacts
A new plate with modern point subassembly condenser has been designed, produced, and is now available.
This specifically designed and produced assembly:
- Locates and fixes the modern point assembly properly in relation to the distributor cam high point and rotor brass tip
- Mounts the condenser on the point plate to shield it and reduce engine heat effects
The new plate with modern point sub assembly and condenser incorporates:
- Fixed pivot pin location for proper cam and rotor contact relations and reproducible point assembly replacement
- Current production tungsten contact points
- Condenser of modern materials, construction, and sealed against moisture for long life
- Two hold-down screws for easy setting, adjustment, and point assembly replacement
- A fiber/ low friction rubbing block for long life
- A copper current carrying strap in parallel with the steel spring for low electrical resistance
The use of modern and standard components allows availability and easy replacement of the point assembly and condenser. Both are procurable from automotive supply stores while on the road. The points and condenser were used on the Ford V8, 1957-1974 years.
The plate was stamped by the original dies, only modified to eliminate unnecessary holes and include the new holes. It consequently properly fits the distributor housing.
An additional feature of the new plate assembly is the easy replacement of components and accurate setting of the point gap opening.
Installation of the plate is straight forward:
- Remove the old plate and condenser
- Install the new plate, old pigtail, or a new longer one for ease of connection
- Replace the original condenser with a non-connected dummy (for external appearance) or leave open
- Adjust the point gap and retime the engine
A unique, easy, and accurate point gap adjustment procedure follows:
Distributor Out of Engine
- (a) Place the furnished 0.020" plastic gage in a vertical position between the point contacts. They are to be set for 0.020" plus or minus .002" gap. Loosen the two hold-down screws to just allow the point assembly to move with some friction when the stationary point is moved by hand. Install the cam, washer, and hold-down screw.
- (b) Tighten the cam just enough so it rotates as the distributor shaft is turned. Turn the shaft and cam CCW (direction of engine drive) and allow the flat to contact the point rubbing block. Push the points to contact the cam then continue to slowly rotate the shaft. The cam will ride against the rubbing block, moving the point assembly around its pivot point. Continue the shaft rotation until the cam high point is reached and the point assembly maximum rotation is observed. Tighten the 2 hold-down screws. The point gap is now adjusted for 0.020" gap.
- (c) If the shaft is rotated through 360 degrees, the concentricity of the shaft and cam can be observed. A perfect cam, shaft, and bearings would show the same "just touching" the cam high point at 4 places.
- (d) Remove the plastic feeler gage. The points will spring closed. The points should open and close as the shaft is rotated. The gap openings should be within about plus or minus .001" of each other for uniform operation.
Distributor in Engine
The distributor shaft is held fixed by the engine. The above procedure is followed with the cam loose and instead rotated by hand.
- (a) Lubricate the cam with cam lubricant for long life of the point rubbing block and cam.
- (b) Install the rotor, distributor, plug wires, and all connections as usual.
- (c) Set the ignition timing. Nu-Rex Precision Timing Kit or Nu-Rex Nu-Wrench timing tool is recommended for accurate and reproducible timing settings.
So, install a new "Upper Point Plate with Modern Points and Condenser" and have many, many miles of maintenance free, reliable driving performance.
The new plate assembly was designed for and is being produced by "Genuine Nu-Rex."
1 "Ignition Failure & Faults - Distributor Upper Plate with Modern Points", MODEL A TRADER, Mar/Apr 1992, pgs 2,3.
2 "Ignition Timing the A", MODEL A TRADER, Jan/Feb 1992, pgs 2,3.
3 "Timing the Model A Distributor - Distributor-Cam Adjustment Simple & Accurate", MODEL A TRADER, Sep/Dec 1992, pg 4.
4 "The 'C' Spark - Testing the Voltage & Condition of Your Ignition System", MODEL A TRADER, Jan/Feb 1993, pg 16.