See Figures 1 and 2
- Locate the timing marks and pointer on the lower engine pulley and engine front cover.
- Clean the timing marks and pointer.
- Mark the proper timing mark (see Tune-Up Specifications for the correct timing for your engine) and the pointer with white chalk or day-glo paint. Attach a tachometer to the engine.
- Attach a timing light according to the manufacturer's instructions.
- Disconnect any and all vacuum lines from the distributor, and plug the vacuum line(s) with the end of a pencil, a golf tee, or any other suitable object.
- Check to make sure that the timing light wires are well clear of the fan assembly. Start the engine.
Follow the precautions discussed earlier for working on an automobile with the engine running.
- If the recommended engine idle speed is in excess of 500 rpm, set the idle at 500 rpm for purposes of setting the ignition timing. If the recommended idle is below 500 rpm, do not alter it. Refer to Fuel System for idle speed setting procedures. In all cases, references in this procedure are for idle speeds with the engine at its full operating temperature.
- Aim the timing light at the timing mark and pointer on the front of the engine. If the marks which you made on the pointer and timing mark align when the timing light flashes, set the idle to its proper specification, remove the timing light and tachometer, and connect the vacuum lines at the distributor. If the marks do not align when the light flashes, continue with the procedures for ignition timing adjustment.
- Stop the engine with the timing light still connected. Loosen the distributor hold-down clamp slightly.
- Start the engine again, and observe the timing mark and pointer with the timing light. Timing may be advanced by turning the distributor of a six-cylinder engine counterclockwise. On V8 engines, the timing is advanced by turning the distributor clockwise. When the proper timing has been attained (when the paint marks on the pointer and the timing mark align), stop the engine. Tighten the distributor hold-down clamp. Restart the engine and check the timing to make sure that it was not altered while you tightened the hold-down clamp.
- On all engines, except pre-1968 six-cylinder models, the centrifugal advance must be checked for proper operation. Start the engine and accelerate it to approximately 2,000 rpm. Properly aim your timing light at the mark and pointer. If the ignition timing advances, the centrifugal advance mechanism is functioning properly. Note the engine speed when the advance begins, and the amount of advance which is attained. Stop the engine.
- On all engines except pre-1968 high-performance engines equipped with centrifugal advance distributors, connect the vacuum line at the outer side of the diaphragm. Start the engine and accelerate it to approximately 2,000 rpm. Note the speed when the advance begins and the amount of advance attained. On pre-1968 six-cylinder engines, any advance indicates that the vacuum advance is in proper working order. On all others equipped with vacuum advance, the timing should now advance sooner and farther than before the vacuum lines were connected. If this occurs, the vacuum advance is working properly. Stop the engine.
- On dual-diaphragm distributors, check the vacuum retard operation by connecting the intake manifold vacuum line to the inner side of the diaphragm. Start the engine and adjust the carburetor to its normal idle speed. The initial timing should retard to approximately top dead center (TDC) if the initial ignition timing is correct. On some engines, the timing may retard as far as six degrees after top dead center (ATDC).
- If the vacuum advance (or vacuum retard, in the case of dual-diaphragm distributors) is not functioning properly, it will be necessary to remove the distributor from the engine and have it tested on a distributor testing machine. Refer to Engine And Engine Overhaul for distributor removal procedures. If either diaphragm is leaking or cannot be calibrated to specifications, it will be necessary to replace the diaphragm unit.
- If all vacuum advance and retard units are found to be in proper working order, remove all testing equipment from the engine.