The distributor gear is an invaluable component for an engine. In most cases, the oil pump is driven off of the distributor gear, and the spark-timing is always driven off of the distributor gear. This gear is found at the bottom of the distributor shaft, and it engages with a gear machined into the camshaft. The distributor gear is a very small part with a very large and important role within the confines of an engine.
Distributor gears are made from many different types of materials. For a conventional cast iron camshaft, the distributor gear is made out of cast iron. For billet steel roller type camshafts, the distributor gear is made out of bronze. Running a cast iron gear on a steel camshaft will often result in broken parts.
The ratio of the distributor gear is such that it turns the distributor one full turn for every full turn of the crank shaft, and every two full turns of the cam shaft. This ensures that the spark plugs will fire at the correct position of the piston. The gear is attached to the distributor shaft with a steel roll pin. This roll pin keeps the gear locked onto the shaft in the correct position. If the pin breaks or becomes loose, the spark timing will become erratic and the diagnosis is ofter difficult to make.
Distributor gear contact with the cam gear should be checked to make sure the two gears are engaging each other correctly. This is done by applying a white grease to the distributor gear teeth and installing the distributor into the engine. The engine is then turned one revolution and the distributor is removed, and the pattern of the gear contact is noted by looking at the pattern the gears made in the white grease. The distributor is then shimmed, as needed, to produce a wear pattern that is right in the middle of the two gears. This is an often costly oversight by inexperienced mechanics and novice engine builders.
The gear is oiled by an internal oil passage within the engine block and in normal use, rarely ever fails to work correctly. When ordering a high-performance distributor, do not forget to tell the manufacturer what type of camshaft is installed in the engine. This will ensure that the proper gear is placed onto the distributor to provide a long and trouble-free coexistence within the engine.