In this article we tackle one of the most requested topics – timing lights. It may be basic knowledge for many but it seems there’s still a lot of confusion surrounding the correct use of a timing light.
What is it?
A stroboscopic or timing light is a tool used to determine at exactly what angle a spark event is occurring.
How does it work?
In order to do this, we need to have a timing mark (let’s use 0 degrees for this example) on the spinning part of a harmonic balancer or cam gear as well as a fixed mark on the engine or a backing plate.
When the light flashes and these marks are aligned we know that the engine is firing at exactly 0 degrees.
Keep in mind if the light is being aimed at the crankshaft (on a 4-stroke engine) we won’t know whether the engine is firing on the Compression or Exhaust stroke.
If we point the timing light at the camshaft (if possible) we can then determine the ignition angle as well as the firing stroke. This can be very handy when we’re trying to get an engine to run for the first time.
How do we get the timing light to flash?
A timing light requires power and normally has a couple of batteries inside or some clamps to use the engine’s 12V power supply.
It should also have an inductive clamp – this is the part that clips over a spark plug lead in order to trigger the light.
If you don’t have spark plug leads you can try one of the following:
If you’re having trouble getting a timing light to fire consistently (or at all) try increasing the gap the spark needs to jump (not too big or you’ll risk damaging the coil). Keep in mind the spark doesn’t even need to be firing into a cylinder, you could be cranking the engine and have the spark jumping a 5mm gap to a screwdriver.
There’s a “Spark Tester” tool that could come in handy if you find yourself doing this a lot, with a threaded rod grounded on one end and the other end attached to the high output of the coil. You will need to adjust the threaded rod to achieve whatever gap makes the timing light flash.
It’s also important to know what type of timing light you’re using – Dialback or Fixed.
Dialback timing lights have a knob or a programmable display that allows you to delay the flash in order to line up the timing marks. You can then read the ignition angle off the light’s display based on the delay time it took to line up the marks.