Points are a simple mechanical switch
for opening and closing the ignition coil
’s primary circuit
. This switch is set inside the body of the distributor
and a cam
mounted on the distributor shaft actuates the switch, breaking the primary circuit which cause a high tension spike to be passed from the coil to the rotor
and on to the spark plug
Points are a very reliable system for controlling the ignition circuit but they do require periodic adjustment to maintain the proper timing of the current spikes. Every time the switch opens the current arcs between the contacts causing carbon buildup. This buildup increases the impedance of the circuit and affects the amount of time the switch is opened. The amount of time that the switch remains open is called the dwell. Whenever points are cleaned or replaced the dwell must be reset to factory specs. This is most easily done using a feeler gauge to measure the gap between the contacts at the wide open point. A more accurate way is to use a dwell meter that reads the actual timing of the opening of the circuit. The dwell is physically adjusted by changing the distance between the points and the cam. It is an easy process but it’s tedious to get it just right. The points should be checked before you adjust the timing as stable timing is dependent on the points being in proper order.
note: Most late model vehicles replaced the points system with an electronic ignition that requires no adjustment.