How to Use Timing Lights

The purpose of the timing light is to indicate top dead center on the number 1 cylinder and give a visual reference to use to advance or retard the timing. The ignition timing is the point that the spark plug fires in the power stroke. Fuel burns at a specific rate in an engine depending on the compression in the engine. The firing of the spark plug must be far enough in advance of the power stroke so that as much of the fuel as possible is burned in the power stroke.

Instructions

1. Hook the timing light's power cables to the battery posts. Attach the spark wire probe to the number "1" cylinder's spark plug wire. Set the timing light indicator dial to "0." Make sure all of the cables are clear of all moving parts, such as the fan, belts and pulleys.

2. Start the engine and set the timing light to the number of cylinders. If the car is a 4-cylinder (four cylinder holes), set the timing light to "4." If it is a 6-cylinder, set the light to "6." For 8-cylinder engines, set the light to "8." Pull the trigger on the timing light and shine it down on the crankshaft pulley or harmonic balancer. There is a plate right above the balancer or pulley. On the plate there will be a "0" in the middle and then numbers in increments up to 40 on both sides of the "0" mark. One side, usually the left side, will have the letters "BTDC," which means "before top dead center" and the other side will have "ATDC" or after top dead center. The one that your interested in is BTDC.

3. Pull the vacuum advance hose off and plug the port in the carburetor with a piece of rubber hose and a screw, if the vehicle is equipped with an early style distributor. If it is a computer-controlled vehicle, unplug the shorting bar. The shorting bar is a plug next to the distributor directly in-line with the distributor.

4. Allow the engine to idle. While shining the light on the timing plate with the engine idling, rotate the timing knob on the timing light until the line on the harmonic balancer lines up with the "0" mark on the timing plate.

5. Read the number displayed on the timing light under the knob. Check this number with the timing number on the vehicle adjustment information tag under the hood of the vehicle. It will say, for instance to set timing to four degrees before top dead center at idle. If the number on the knob on the timing light is different then the timing must be adjusted.

6. Loosen the bolts at the base of the distributor and rotate the distributor slightly and check the timing again by turning the knob until the line is at the "0" mark. If the number is getting closer keep going until it is on the mark. Rotate the distributor the other direction if it is getting farther away. When the target degrees BTDC is reached, tighten the bolts in the distributor. Plug the shorting bar back into its socket or plug the vacuum line back into the carburetor.

Tips & Warnings

• Engines are not totally efficient due to so many changing factures such as differences in temperatures and humidity and altitude. Expansion and contraction in the engine and differences in the tolerances in the engines are a few of the factures that have to be dealt with.