GM Corvette 1963-1982 Repair Guide

Ignition Timing


ADJUSTMENT 1963-80 Vehicles

See Figure 1

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Fig. Fig. 1: View of a common timing mark location and scale

  1. Warm the engine to normal operating temperature and check the idle speed. Adjust the idle speed to specifications, if necessary.
  3. If so equipped, disconnect and plug the vacuum advance hose from the distributor.
  5. Connect a timing light according to the timing light manufacturers instructions. DO NOT use a timing light which requires piercing of the spark plug lead. Timing lights which have a lead that must be installed between the plug and the plug wire may be used with conventional ignition systems. On HEI ignition systems, use ONLY an inductive pickup-type timing light.

Timing lights requiring a 12 volt DC power source (battery) may be connected as follows: Connect the positive timing light lead to the BAT terminal of the alternator; the negative timing light lead to a good engine ground.

Be careful not to ground the positive lead to the alternator case.

  1. Locate the timing tab (metal tab marked in graduations) which is attached to the timing cover. Locate the single mark on the vibration damper (one groove). Clean both the timing tab and the damper marking. Use chalk to accentuate the marks if necessary.
  3. Be sure that all wiring and tools are clear of the fan and belts. Start the engine and allow it to idle. Aim the timing light at the marks and note where the vibration damper mark aligns with the timing tab.

The "O" marking on the tab is the top dead center (TDC) mark and all the before top dead center (BTDC) marks are on the "before" (advance) side of the zero, or the "A" (advance) side of zero. Later models are marked to indicate Before and After.

  1. Loosen the distributor clamp (holddown) bolt and slowly rotate the distributor as necessary until the damper mark is aligned with the specified mark of the timing tab. Tighten the hold-down bolt and recheck the timing.
  3. Turn the engine off and remove the timing light.
  5. If so equipped, unplug and reconnect the vacuum advance hose to the distributor.


Refer to the underhood emissions label for the proper timing adjustment procedure.

1981 Vehicles

Refer to the underhood emissions label for the proper timing adjustment procedure.

1982 Vehicles

The ignition timing of 1982 models is adjusted in basically the same manner as previously described (1963-80). The exception to this is that the EST BYPASS wire from the distributor must be disconnected prior to the timing adjustment. Trace the four wires from the distributor housing which join at a common multi-connector, close to the distributor. Follow the tan wire with a black stripe (EST BYPASS wire) from the multi-connector. Past the multi-connector, the EST BYPASS wire has its own, single connector.

Separate this connector before adjusting the timing. While the EST BYPASS wire is disconnected, the CHECK ENGINE light on the instrument panel will illuminate. After adjusting the timing, reconnect the EST BYPASS connector; the CHECK ENGINE light will go out.

It is not necessary to adjust the idle speed on 1982 models prior to the timing adjustment, though the engine must be at normal operating temperature.