Types of Timing Lights

by Don Bowman

Timing lights are necessary to adjust the firing time of the ignition for the proper combustion of fuel. Fuel burns at a constant rate depending on compression in the engine. As the engine's RPM increase, the time that the engine is on a compression and power stroke decreases, although the fuel burn time remains fairly constant. In order to burn the same percentage of fuel as at an idle, the timing of the spark must be advanced sufficiently to give the fuel more time to burn.


There are various timing lights, all serving the same purpose. These timing lights differ in RPM range, function, and ability to operate on multi-spark systems and multi functions. The functions can include a dwell meter, a tachometer, timing manual advance, and an ability to work on four-, six- and eight-cylinder engines (and also on two-cycle engines).


The standard inductive timing light is a nonadjustable xenon tube light. It will show the timing mark at an idle; anything above an idle would have to be interpolated. The standard digital inductive timing light will be capable of timing both a two-cycle as well as a four-cycle engine. Another good feature is a knob that allows the timing light to advance the light to show the timing at different RPMs. When the engine is at an idle, the knob should be adjusted so the timing mark on the crankshaft pulley is on the "0" mark on the timing pointer. Once the mark has been adjusted to the "0" mark on the pointer, the knob will indicate the amount of degrees that the timing is advanced or retarded at that point. As the RPM is increased to 2,000, the timing mark will move counterclockwise as the ignition advances the spark. A turn of the knob will bring the mark back to the "0" mark on the pointer. A look at the knob will indicate the amount of advance at that RPM. The better timing lights will also have a tachometer incorporated in the unit. It will have a switch to toggle from RPM to timing. Some of these lights will have two trigger buttons to advance the timing as opposed to a knob. The best units will also have a dwell meter to check the amount of time the coil is being charged. In a points-type ignition, this can save the points from burning or pitting by giving the capability to accurately set the point gap.


In a multiple spark distribution (MSD) system, a special timing light is needed to indicate the proper initial timing. A multiple spark system gives off a series of sparks through a range of degrees of timing. For this reason, the timing light must indicate the beginning of the sequence. This is where many timing lights are deficient: they get confused with more than one spark and then pick a random spark. Always ask or check the timing light to see if it is MSD-compatible if you have MSD on your vehicle.


Always make sure that the timing light wires are secure and clear of all moving parts. Never attach the inductive pickup close to the exhaust, since it will melt from the heat. Care should always be taken attaching the inductive pickup to an MSD ignition wire. The safest way is to attach it to the number "1" wire with the engine off.


Connect the battery connectors to the proper terminals. Connect the inductive pickup over the number "1" wire. Make sure all wires are free of interference. Start the engine and aim the light at the harmonic balancer and the timing plate on the timing cover. With the engine idling turn the timing knob on the back of the timing light or push the trigger, if so equipped, until the timing mark on the harmonic balancer lines up with the "0" mark on the timing plate. Read the number of degrees of advance or retard on the timing light. Adjust the timing as necessary to match the recommended timing on the sticker under the hood that gives the timing specs. Raise the RPM to 2,500, perform the same procedure and check the light for the total advance.

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