Timing should be checked at each tune-up. The timing marks consist of a notch on the rim of the crankshaft pulley or vibration damper and a graduated scale attached to the engine front (timing) cover. A stroboscopic flash (dynamic) timing light must be used, as a static light is too inaccurate for emission controlled engines.
There are three basic types of timing light available. The first is a simple neon bulb with two wire connections. One wire connects to the spark plug terminal and the other plugs into the end of the spark plug wire for the No. 1 cylinder, thus connecting the light in series with the spark plug. This type of light is pretty dim and must be held very closely to the timing marks to be seen. Sometimes a dark corner has to be sought out to see the flash at all. This type of light is very inexpensive. The second type operates from the car batterytwo alligator clips connect to the battery terminals, while an adapter enables a third clip to be connected to the No. 1 spark plug and wire. This type is a bit more expensive, but it provides a nice bright flash that you can see even in bright sunlight. It is the type most often seen in professional shops. The third type replaces the battery power source with 110 volt current.INSPECTION & ADJUSTMENT
To check and adjust the timing:
- Warm up the engine to normal operating temperature. Stop the engine and connect the timing light to the No. 1 (left front on V8, front on six) spark plug wire. Clean off the timing marks and mark the pulley or damper notch and timing scale with white chalk.
- Disconnect and plug the vacuum line(s) at the distributor. This is done to prevent any distributor vacuum advance.
- Start the engine and adjust the idle speed to that specified in the "Tune-Up Specifications" chart.
- Aim the timing light at the point marks. Be careful not to touch the fan, because it may appear to be standing still. If the pulley or damper notch isn't aligned with the proper timing mark (see the "Tune-Up Specifications" chart), the timing will have to be adjusted.
TDC or Top Dead Center corresponds to 0 degrees. B, or BTDC, or Before Top Dead Center may be shown as BEFORE. A, or ATDC, or After Top Dead Center may be shown as AFTER.
- Loosen the distributor base clamp locknut. You can buy trick wrenches which make this task a lot easier. Turn the distributor slowly to adjust the timing, holding it by the body and not the cap. Turn the distributor in the direction of rotor rotation (found in the "firing Order" illustration in Chapter 3) to retard, and against the direction of rotation to advance.
- Tighten the locknut. Check the timing again, in case the distributor moved slightly as you tightened it.
- Replace the distributor vacuum line. Correct the idle speed if it changed.
- Stop the engine and disconnect the timing light.