How to use a timing light
With the introduction of modern fuel injected engines and computer controlled distributorless ignition systems, timing lights began to go the way of the DoDo, however they still are a necessary tool that every technician and do-it yourselfer should be familiar with and comfortable using. What is a timing light? In simple terms it is nothing more than a strobe light that fires in synchronization with the engine’s ignition system. Most lights use a three wire harness with color coded battery clips on two of the cables, and an induction pickup on the third. Two of the connections go directly to the battery, or the back of the alternator if close by, (red to the positive battery terminal and black to the negative battery terminal), the third is usually clipped around the #1 plug wire. The induction pickup registering the secondary ignition voltage is how the light is triggered. So when the plug fires, the light flashes, simple. Next, using white chalk, or a paint pen, paint the timing mark on the harmonic balancer, making sure the white paint is only in the groove. This will help in making the timing mark more easily seen while adjusting timing. 1.) Disconnect the vacuum line going to the vacuum advance canister on the side of the distributor, (if equipped), making sure to plug the vacuum line. 2.) Start the engine and let it warm up to operating temperature. 3.) Now aim the timing light at the balancer and timing marks and adjust the timing as necessary and according to specifications. Most engines have distributors that can be rotated to adjust ignition timing. Depending on the engine, and whether the timing is advanced or retarded, it may be necessary to rotate the distributor clockwise or counter-clockwise until the timing mark is at the specified position. Make sure to tighten the distributor hold-down to prevent the timing from coming out of adjustment. If you are using a newer style light with the advance dial feature, you can also use it to check your total timing. Total timing is base timing, plug the advance provided by the vacuum advance, (or computer added advance). Simply rev the engine to 3,000rpm’s and maintain, however, if you aim the light at your timing marks now, you will notice the timing mark on the balancer is now gone. This is because the centrifugal and vacuum advance have advanced the timing beyond the usual 12* degrees indicated on most timing tabs. With the engine still at 3,000rpm’s., rotate the dial on the light until you see the timing mark begin to walk back on to the timing tab. You will notice the further you turn the dial, the timing mark approaches 0* degrees more and more. Once you have advanced the dial to the point the timing mark is sitting at 0* degrees, look at the dial and the number indicated is your total timing. Also it should be noted that some aftermarket performance ignition boxes will interfere with most dial-back timing lights, making them unreliable and require the old style lights and use of a timing tape on the balancer a requirement.