How to Use a Variable Timing Light

Timing lights provide a measurement for engine ignition timing. They are used to synchronize the firing spark to the compression of the engine cylinder. They use an inductive strobe light to line up marks on the crankshaft pulley, or harmonic balancer, with a line on a measurement tab located on the block. The distance between the two marks shows the amount of degrees. A variable, or adjustable timing light has a feature which allows the operator to preset the proper degree setting, according to the manufacturer's specifications. This takes the guesswork out of the adjustment.

Instructions

1

Place the transmission selector on your vehicle in neutral or park. Apply the emergency brake and raise the hood. Disconnect the negative battery cable with a socket. Locate the crankshaft pulley (harmonic balancer) at the front, lower part of the engine. Use a rag to clean the edge of the crankshaft pulley and the metal timing mark tap above it. Look for a straight line etched across the pulley. If you do not see one, use a large socket and breaker bar to turn the large pulley nut until you see the line mark.

2

Take a piece of white chalk and mark the line on the pulley, so it appears plainly visible. Look at the timing mark tab. You will see graduated degree lines, beginning with "0" in the middle. The degree marks on one side of the line will be indicated by an "A" or "AFT," which means after top dead center (TDC). The degree lines going in the opposite direction will be marked with a "B", or "BF," or some variation, and they indicate degrees before TDC.

3

Mark the "0" line on the timing tab with the chalk. Reconnect the negative battery cable with a socket. Hook up the negative (black) lead of a variable timing light to the negative lead on the battery. Hook up the positive (red) lead of the timing light to the positive lead on the battery.

4

Refer to your owner's manual for the proper location of your engine's number 1 cylinder. It might be on the left or right side of your engine as you face it. Take the conductive clip on the timing light and clip in around the number 1 wire.

5

Locate the distributor and look down at its base where it enters the engine block. You will see a distributor base clamp held by a bolt. Use a socket and extension to loosen the bolt only enough to allow the distributor to rotate slightly. Do not turn the distributor any great amount -- only enough to test its movement, which should require medium hand pressure.

6

Pull off the vacuum hose on the side of the distributor that attaches to the vacuum advance diaphragm. Plug the end of the hose with a small bolt. Start the engine and let it warn up to operating temperature. Make sure the choke deactivates completely.

7

Refer to your owner's service manual for your recommended timing setting in degrees. You might find the specification listed on a plastic sticker or placard affixed to the fan cowl or radiator support frame. The timing number will be listed in degrees, such as 12 degrees BTDC.

8

Pick up your variable timing light and look at the digital scale in the window and adjustment knobs. The adjustment might be indicated with push-button arrows that show up and down directions to advance or retard the timing. The timing light might have a dial, which turns. Check the instructions.

9

Adjust the dial or buttons until the proper amount of degrees shows on the timing light window. Remember that it will indicate BTDC and ATDC. In most cases, you will need the BTDC selection. Point the timing light down at the crankshaft pulley and look where the strobe lights illuminate the chalk marks. The chalk marks should align the crankshaft pulley mark with the "0" mark on the timing tab. If they do not align, manually rotate the distributor until both zero marks align. Shut the engine off.

10

Tighten down the distributor base bolt with a socket and extension. Start the engine. Recheck the timing marks to make sure they have not changed. If they align, shut the engine off. Pull the bolt from the vacuum line and reconnect the line with the vacuum advance diaphragm on the distributor. Unhook the timing light leads.