Timing the Model A Distributor
Distributor-Cam Adjustment Simple & Accurate
Timing the Model 'A' ignition by rotation of the distributor cam is a "hit and miss," difficult and inaccurate method. The "lash" in the cam drive mechanism and no cam-degree measurement method are the sources of the problem.
An article, "Ignition Timing the A," in the Model A Trader - Jan/Feb 1992 1 issue discussed the theory for optimum timing. It also presented tools and a method for measure of the timing under engine running conditions.
The tools consisted of the crankshaft degree indicator, cutaway distributor cap, and offset cam adjusting wrench shown in Figure 1 of this and the referenced article. A conventional timing/ strobe light, was used to illuminate and measure the actual degree of spark retard /advance while the engine ran. The instructions supplied with the kit also suggested timing settings based upon a large number of cars tested.
Timing change or adjustment by the cam rotation is difficult because there is no absolute reference for the cam-contact points position within the distributor. A cam-contact points degree measurement scale and method to "change/ set" the cam position a KNOWN number of degrees has been developed and tested.
The measuring/adjusting tool is a crankshaft degree scale keyed to the distributor. It shows the cam relative degree position in conjunction with the offset cam wrench. A desired known specific crankshaft timing degree change can now be made, measured and reproduced.
Application first measures the degree of initially set or existing relative crankshaft position. The cam hold-down screw is loosened and the cam rotated the desired advance or retard degrees of change; the screw is then tightened. The cam is always held to remove the ever-present "backlash" during adjustment or rotation during tightening. The timing degree change desired was determined by a "timing light" crankshaft pulley measurement following the instructions accompanying the kit.
If a "timing light" is not used, the cam position can be changed a known trial number of degrees. A vehicle road test is next made to determine the engine performance. The need for further change can be determined and KNOWN timing change be made accurately and reproducibly.
1 Copies of the referenced article, or other articles from past issues of Model A Trader, may be obtained from Model A Trader, 1247 Argonne Road, South Euclid, OH 44121 for $1.00 postage and handling.