Sparks — they’re what starts a romance, light up the night sky and set a fire. Setting fire (or igniting fuel) is exactly what we’re talking about today and is one of the (very few) ways to get an engine running.
In any modern petrol engine, you only really need 4 things to create power: air, fuel, compression and ignition. These 4 things set off a series of explosions thousands of times per minute that turn potential energy into rotational energy and heat energy that (eventually) turns the wheels or goes out the exhaust.
So if this ignition source (or spark) is so important, wouldn’t a pilot light be basically sufficient? And why did someone put timing in the title of this post? These are both really valid questions that we definitely didn’t think of ourselves.
On the most basic level, an engine needs the explosive power of a fuel and air mixture under compression to create a rotational force. If we had a constant source of ignition, the fuel would begin to burn as soon as it entered the engine meaning that none of the explosive/rotational energy could be captured. This is because each spark event has to take place at a specific point in the combustion cycle.
This might be a little tricky to understand but, this all relates to the timing of the engine itself (something we covered last week).
Engine timing (basically) refers to the need to keep multiple parts of the engine in-sync and, that a lot of the engine parts are shafts (i.e. circular on each end). By treating the circular end of each shaft as a clock face (or degree wheel), we can keep track of the position of each shaft while keeping them rotating in time with each other.
This same principal is the very same that allows us to set the correct timing for each spark event to occur. By knowing the position of the camshaft and crankshaft, we can ask for the spark to occur at the most effective time in the combustion cycle (which is measured in degrees before or after the top of each rotation).
Ok, now we know what spark timing is and how it relates to the position of the engine, what difference does it really make?
Put simply, advancing the spark (making it happen sooner in the cycle) tends to let an engine generate a bit more power. However, if the timing is too far advanced, it can introduce engine knock which can cause major damage to the engine components.
On newer cars this is all controlled electronically. However, a big part of servicing older cars included adjusting the timing to be in a set window to help the car run smoothly and make a good amount of power.