Timing and firing order

Section 1: Timing

Timing refers to the precise indication of when the spark plug should fire in relation to piston position in the cylinder. Accurate timing is crucial for engine function and performance.
Spark ignition occurs at the right moment within the four-stroke cycle to ignite the air-fuel mixture in the cylinder. This causes the combustion process which drives the piston.
Ignition timing can be advanced (spark firing just before piston reaches Top Dead Centre, or TDC) or retarded (spark firing just after TDC). Corrective measures have to be made to keep timing accurate.
Timing marks on the engine are used to set the initial timing and to check or adjust it when needed. They’re linked to a timing light which synchronises with the ignition system.

Section 2: Firing Order

Firing order is the specific sequence in which each cylinder in an engine receives its spark to ignite the fuel-air mixture. This order optimises balance and minimises vibrations.
The firing order is determined by the engine’s configuration and design (i.e., inline, vee, flat) and the number of cylinders it has.
A basic four-cylinder engine often uses a firing order of 1-3-4-2, which means the first cylinder fires, then the third, followed by the fourth, and lastly the second.
This firing order is designed to provide a smooth running engine and minimise stress on the crankshaft during operation.
Incorrect firing order can lead to a rough running engine, lost power, increased fuel consumption and even engine damage.

Section 3: Distributor and Electronic Ignition

The distributor is responsible for maintaining the correct firing order. It utilises the distributor cap and rotor to distribute the spark to the correct spark plug.
A conventional distributor operates mechanically, driven by the camshaft or crankshaft. Its disadvantage is wear and tear due to mechanical components.
Electronic ignition systems have largely replaced distributors in many modern engines. They generate a more reliable spark and don’t have the mechanical parts that can wear out.
Electronic ignitions are controlled by an engine control unit (ECU) or ignition control module which decides when and which spark plug needs to fire.

Remember that understanding the interactions between timing, firing order, and the distribution of the spark is a fundamental aspect of working with spark ignition systems.