How To Use A Timing Light

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A timing light is an excellent tool for any car restorer's garage, but it can be intimidating to know how to use it. How do you use a timing light?

The basic process of using a timing light to double-check the timing of the ignition is as follows.

  • Determine if Your Car Needs Timing
  • Ensure the Engine is off
  • Connect the Red - Black Connectors to Battery
  • Attach padded clip to the Number 1 spark plug wire
  • Start the Engine
  • Aim Timing Light at the timing marks
  • Adjust the distributor until aligned and reading correctly.

As a lover of classic cars, I know how frustrating it is if a car isn’t running at the right timing. The car’s timing refers to the ignition and the “time” that the spark plug fires, creating an explosion inside the chamber. The correct timing can affect your engine's performance and ability to run smoothly. While most technicians know how to adjust the timing on a classic car, the process can be a bit intimidating for a novice. (The first time I used a timing gun, I was so frightened that I asked a mechanic friend to come over and do it while I watched).

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How Do I Know if My Car’s Timing Needs Adjustment?

A car that is not running in time will show tell-tale signs of a rough idle, pinging, loss of power, or even a check engine light, but this does not always mean a car’s timing needs to be adjusted. Most modern cars have electronic ignition, which means that an internal computer adjusts the timing automatically. Suppose the sensor lights are illuminated in the instrument panel (usually a check engine light). In that case, it is best to take the car to a certified technician to run the DTC (Diagnostic Trouble Code). They will be able to tell if the car’s timing is off or if there is a faulty sensor giving a bad reading.

The Four-Cycle Stroke of an Internal Combustion Engine

Generally, the only cars that need a timing adjustment are older classic cars with a designated four-cycle stroke. (This refers to the four positions a piston is in at any given time - Intake, Compression, Combustion, and Exhaust). As the intake valve opens, air and fuel are drawn into the chamber (intake stage). As the piston head moves upward, the gas and air are compressed (compression stage). The spark plug fires as the piston reaches its optimal position (combustion). And the explosion forces the piston to retreat as the exhaust valve opens to allow burnt fumes to escape through the exhaust (exhaust stage).

Locate the Number 1 Spark Plug Wire

Since the car's timing is set to the number one chamber, consult the owner’s manual to verify which spark plug wire is connected to the first chamber of the firing order. One of the clamps on the timing gun will need to be attached to the wire, but for now, just identify which wire is the right one.

How To Use A Timing Light

Using a timing light just takes a little bit of effort and some patience. There are several steps to using a timing light, as are detailed below.

Ensure the Engine is Off and Battery Terminals are Clean

The first thing to do is to ensure that the engine is off and that the battery terminals are clean enough to make a good connection. If not, spend a moment cleaning the terminals. The timing gun will be hooked up to the battery for power, so ensure that no residual battery acid is interfering with the electrical connection.

Consult the Owner’s Manual and Find the Location of No. 1 Chamber.

Not every engine is built with the same firing order. The sequence is the order in which the spark plugs fire to maximize power and performance. The firing order helps minimize vibrations and engine knocks. In addition, make a note of the location of the number one cylinder.

Connect the Red and Black Clamps on the Timing Gun to the Battery.

Locate the red wire and connector on the base of the timing gun, and one at a time, connect the red wire to the positive terminal and the black to the negative. (If you don’t know which is, look for the + or - symbols on the battery).

Attach the Large Clip to the Number 1 Spark Plug Wire

The most oversized padded clip should be fastened to the spark plug wire that leads to the number 1 cylinder. The clip should go over the outside of the wire. This clamp is sensitive enough to read when an electrical pulse flows through the wire from the distributor to the spark plug.

Start The Engine. Allow it to Warm Up.

Start the engine and allow the car’s engine to heat (about ten minutes).

Take the Timing Light and Aim it at the Timing Marks.

Take the timing light and squeeze the trigger. Aim the light directly at the timing marks. The clamp hooked onto the spark plug wire should detect every time an electrical current travels through, telling the spark plug to fire. This current makes the light flicker on and off, much like a strobe light. The timing marks should appear to be standing still. If they are, your car’s timing is correct, and no adjustment is needed.

The Timing is Off and Needs Adjusting

At the base of the distributor staff, right below the distributor, locate the hold-down clamp. Loosen the clamp so that the distributor is free to rotate on the shaft. Carefully move the distributor to the right or left as needed.

Aim the Timing Light at the Timing Marks

Once you have moved the distributor, aim the timing light back at the marks. If it is farther away from the marks, the distributor must move in the opposite direction. Grab the vacuum advance and nudge the distributor back until the marks line up, and the timing gun makes it appear as if the marks are not moving. This may take a couple of adjustments before finding the right setting.

Once Aligned, Tighten the Distributor Hold Down Clamp

Re-tighten the hold-down clamp, and be careful to move the distributor. Reconnect the vacuum hose. Pick up the timing gun to double-check the timing. If not, repeat the process all over again.

Author’s note: I like to listen to the car as it idles to ensure the engine seems right. The last thing I want is an engine running out of time. If the engine struggles to maintain a consistent rhythm, double-check the timing again to ensure that the readings are correct. (It is easy to have the distributor slip while refastening the hold-down clamp). If everything looks good, disconnect the timing gun and put it away because the project is done.