Model 'A' Ignition Timing - Making It Right

Distributor rotor position
The rotor position shown above is the proper position with the timing pin in the gear depression and piston #1 at TDC. The dashed line shows the position of the rotor when #1 fires with the spark lever fully advanced (down).
NOTE: This is for reference only and not a suitable method for final adjustment of the timing.

Introduction
Timing the Model 'A' Ford is a subject frequently covered over the years. Every version I've read is either more complex than necessary, or too inaccurate. The following method is not only quick and simple, but probably more accurate than Ford expected.

Preliminaries
Before adjusting the timing some basic distributor checks are in order. With everything assembled check the travel of the spark advance relative to the opening in the side of the distributor body. The protruding lever should be against one wall of the opening with the lever down and against the other wall with the lever up. Adjust or bend the linkages as required. This will insure full use of the advance for maximum performance.

Prepare to adjust the points by removing the distributor cap, body, and rotor. Grasp the distributor cam with your thumb and forefinger, and attempt to rock or move the shaft back and forth. There should be no discernible movement laterally. Any movement indicates worn bushings and/or shaft. The distributor will still function, but the point gap will vary by a corresponding amount. Keep in mind the recommended point gap is .018"-.022", not .013"-.027"!

Perform a similar check of the upper "Breaker" plate. Grasp the plate by the protruding arm. Move the plate fore and aft. Again, the point gap will fluctuate by a corresponding amount. Add the two amounts together and see the potential problem! Any play can generally be corrected at this time without replacement of the breaker plate. See Rebuilding the Model 'A' Distributor

The last check is for cam uniformity. Turn the engine with the hand crank and position one of the cam lobes under the point rubbing block to open the points fully. Carefully measure the point gap and adjust to .020". Now rotate the engine 180 with the crank, rotating the cam to the next lobe. Carefully measure the point gap and note and variance from your original setting. Repeat the process twice more until all four lobes have been checked. They should all be identical but often vary. If they vary, readjust the points to average .020" until proper repairs can be made.

Be certain the point contacts are properly aligned and square. Remove the breaker plate and adjust if required.

Timing Pin and Timing Gear
one problem often encountered is difficulty locating TDC (top dead center) of piston number one by use of the timing pin. This is due to modern replacement timing gears having a small dimple unlike the one shown below. Any time prior to engine assembly this can be corrected carefully with a 1/4" twist drill. Drill just deep enough to enlarge the depression to 1/4" diameter.

Original timing gear
Model 'A' Timing pin modification
Original timing gears had a deep depression which works well with the original timing pin. Modern replacements require either correction or creative modification of the timing pin to locate the timing mark.

If your engine rebuilder was too rushed to take care of this problem the timing pin can be modified. Assuming you don't have a lathe in your garage you can chuck the threaded end of the pin into a 3/8" drill. While running the drill, shape the end of the timing pin by lightly grinding with a running bench grinder. Position the drill so the rotation of the pin is approximately 90 to the rotation of the grinding wheel. Don't rush it or it will not retain it's center. The tip should not be so sharp as to scribe the timing gear while locating the mark.

Adjusting the breaker points
If you've followed the guidelines above you are ready to move on. If not, adjust the points now. The points must always be adjusted prior to the ignition timing! Reducing the point gap subsequent to timing adjustment (or any other time) retards the timing. Conversely, enlarging the gap will advance the timing.

Setting the Timing
Finally to the heart of the matter!

  1. Use the timing pin to locate TDC of number one. This is the only accurate method short of a long drawn out process with a dial indicator. Other methods will only get you within 5-10 degrees without some extra luck.
  2. With the distributor body installed, raise or retard the spark lever on the steering column to the top of it's travel. This is done in case the distributor body limits the rotation of the breaker plate.
  3. Loosen the cam screw and rotate the cam into position ready to open the points for #1 as shown in the following illustration. If the cam seems excessively sticky on the shaft then use the rotor to turn it.

    Direction of rotation
    This image shows the distributor cam in position ready for the points to break on #1. Tightening the screw to lock the cam removes the backlash in the gears and shafts, and prepares the cam to open or break the points at the slightest rotational move of the crankshaft.

  4. Begin tightening the screw. This removes the backlash in the system and the cam should remain as close to touching the rubbing block on the points as possible without opening the points. This may require multiple efforts to get it ideally positioned.
  5. The final check is to simply turn on the ignition switch. Using the screwdriver at the cam screw, turn it clockwise as if tightening the screw. The SLIGHTEST movement of the screwdriver and cam in the opposite (counter clockwise) direction should clearly spark the points. If the points won't spark the setting is too tight and too advanced and the points aren't closing. If there is any noticeable movement of the cam before the spark then the setting is too far retarded. Don't forget to turn off the ignition. Leaving it on with the points closed may result in a dead battery or burned out coil!

The actual timing sequence is short and simple. With a little practice the points can be changed and set, and the timing set accurately in two to five minutes.

Additional tips

  1. If the car has been running, locate TDC with the timing pin before loosening the cam or removing the rotor. This will allow the use of the rotor to let you know you are approaching #1.
  2. Eliminate the problem of cylinder compression turning the engine past the timing mark. As you feel the compression build while approaching #1, pause and let the pressure bleed out of the cylinder.
  3. The installed total length of the spark control rod (linkage) is 17-7/16". With a two tooth Gemmer steering box you may need to adjust the linkage by loosening the lower column tube clamp and upper support clamp and twisting the column tube in the appropriate direction.
  4. Get a large "stubby" screwdriver that fits snug in the cam screw. This will improve sensitivity for checking the motion and spark.
  5. FORGET ABOUT DWELL. If your cam is bad enough that it won't provide adequate dwell, it will likely show problems in other areas such as different size lobes. You may have your distributor fine tuned in every other way and want to experiment. Try timing the car with the points set at .018". This will increase the dwell and coil saturation time. See if there is any noticeable difference at high speeds. It won't make any difference at low and moderate speeds. But remember you will need to check for wear on the point block more frequently!
  6. once the timing is accurately set it doesn't need to done again until the distributor is serviced and the cam removed such as required when changing original points.
  7. Always oil the distributor when checking the points or performing any other service.

 


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