How Stuff Works

Ignition? It’s all in the timing, says Fuzz

Timing Lights

There are a number of methods that can be used to set an engine’s ignition timing, but the timing light is perhaps the most useful to classic car owners.

Timing the point of ignition – well, actually the point at which the spark plugs fire on a spark ignition engine – is crucial to its smooth running. Setting this correctly is only a part of achieving a well-behaved engine, because fuelling, air intake, valve seating, timing and their clearances are all crucial to this desired end.

Once all of these other factors have been established to the greater degree, it’s then… er… time to begin ignition timing.

Ensuring that the spark plug leads have been connected in the correct order is a must before getting around to attaching a timing light, and it is at this point that our tool comes into its own.

Timing lights for the classic car fiddler come in two basic forms – static and stroboscopic.

Static timing lights are useful for establishing the approximate point of ignition but can be a blunt tool when it comes to defining the manufacturer’s stated ideal. However, they are useful to more experienced engine tuners for establishing a datum point from which to start the timing process, before finishing off by ear.

Stroboscopic dynamic timing lights are equipped with a high-intensity bulb, capable of full illumination and extinguishing many thousands of times per minute.

Static timing lights are made by placing a bulb of the correct voltage for the car into a bulb holder and attaching a wire to each terminal. A crocodile clip on the end of each wire is handy, but not essential.

To use the light, it is then connected to the low-tension ignition circuit by attaching one wire to the distributor feed and the other to an earth point on the engine.

The engine is then turned by hand (ignition off ) until top-dead-centre (TDC) is established on the cylinder being timed – normally ( but not always) number one.

This can be achieved using timing marks on the flywheel or crankshaft pulley, or using a TDC whistle in the spark plug socket, or even a simple rod, placed in the spark plug socket onto the top of the piston and noting the point at which it reaches its maximum height.

Remember that four-stroke engines rotate two full times per cycle, so the correct TDC can be confirmed by valve position

(if visible) or by removing the distributor cap and checking that the rotor arm is pointing towards the plug lead terminal for the cylinder being timed.

Once this has been established, if no marks are provided, use some typewriter correction fluid to make some on the crank pulley and engine block. Rotate the engine against normal direction of rotation by about 30 degrees and then slowly turn it back towards its designated ignition point – also often marked, but if not, easy-ish to establish using a protractor.

Now, with the ignition on, but without engaging the starter motor, loosen the distributor’s clamp bolt. Your timing light should not be lit, but if it is, turn the distributor body against direction of rotor rotation until it goes out and then back again to the exact point at which the bulb illuminates. Re-clamp the distributor and you have set the static timing.

Stroboscopic timing lights are usually attached by connecting the two clips to the relevant battery terminals and then the pulse pick-up to number one spark plug lead. Start the engine, run it at the manufacturer’s designated timing idle speed and point the light at the timing marks.

Pull the trigger and the electrical pulse picked up from the spark plug lead will activate the strobe light, making the timing marks appear static.

If the timing marks are misaligned, the distributor clamp may be slackened and the distributor rotated until the marks align properly. Re-clamp the distributor and the engine’s timing is set dynamically.

’Timing the point at which the spark plugs fire is crucial to smooth running’