How do you reset a distributer cap?

Answer 1

This answer is dependent upon the make and model of the unit, but as a general rule, you may require a timing light. This timing light should be connected (dependent on type) to the first spark plug on the boot, which will leave (again, depending on type) a spring sticking up above the spark plug to which you connect the boot.

You will need to locate and mark the timing notch (depending on engine) on the lower fan pulley, and use a parts marker or white-out to fill that notch to make it more visible. Clean off any excess mark.

Note that on many front wheel drive vehicles, this is different. The timing mark is on these vehicles behind a cover plate, on the lower toothed pulley that connects to the crankshaft, which makes these harder to work on.

The objective is to see how far off you are on the timing. The first step is a diagnostic, when you start your engine, point your timing light at this pulley. By this pulley, there is often a mark that allows you to determine how far away you are from time (plus ten to twenty degrees, usually). These numbers refer to the distance between your mark and top dead center (which is defined by when the first cylinder is at the top of its travel with all valves closed).

With the motor operating, the light should flash at regular intervals which, when pointed at the mark, makes it appear to be stationary. Compare this mark to the information listed in the manual for the timing setting on this engine at idle.

If the light appears to jump around, with the old style distributors, you've likely got a loose bearing surface, or loose head within your distributor cap, or potentially a worn cap or rotor, or damaged condensor which is firing off time.

Many older distributors used a system with a mechanical adjustment, a screw by the distributor base, that allowed you to loosen it and twist the distributor (gently) and observe the effect on the timing light's location. This allows you to adjust the system to factory spec.

Note that you never should have a timing system advanced to the point of below zero degrees timing. This may cause reverse motor operation, which will destroy the motor.

On most of the older mechanical distributor systems, as well, there is a vacuum timing advance for accellerative timing of the motor. This is an automatic system, and shouldn't need adjustment, though it can fail and require replacement, or create a vacuum leak which requires replacement of the tube.

On more modern electronic ignition systems, the ECM computer (emissions control) adjusts timing advance, as well as dealing with fuel flows, and is a much more difficult system to troubleshoot, repair, or adjust. It's best to leave these to a certified mechanic.