Car Engine Timing Basics

The relationship between the moving parts of an engine is engineered to extremely high tolerances, kept in check by very precise engine timing. Here is how the car engine timing all works.

It is estimated that there are around 10,000 moving parts within an average internal combustion-powered car. Your car engine consists of a number of rapidly moving parts, including a crankshaft, camshaft, pistons, engine valves, rods, and pulleys. As the piston moves up and down, the valves move correspondingly, in and out. The crankshaft spins, and the connecting rods pull and push. All of this must work in perfect harmony.

Put like that, it is a truly mesmerizing feat of engineering to get all those components talking to each other and meshing to form the machines that we know and love. And in terms of the heart of the beast – the engine – timing is an all-important factor.

With the precise movement of camshafts, valves, pistons, and crankshafts being integral to the internal combustion process, there really is no room for error considering the rate and violence at which these components interact with each other.

Basics of Car Engine Operation

To understand the importance of engine timing, let us understand what is happening within the cylinders of a normal four-stroke engine. The four cycles are:

Air gets sucked in by means of the intake valve, while the injectors deliver fuel.
The fuel mixture is compressed.
The spark plug combusts the fuel mixture, pushing the piston down.
The exhaust valve opens to let out the burnt fuel gases (the exhaust).

In a four-stroke cycle, the crankshaft must turn a full two rotations (or 720 degrees) to complete an engine cycle, rotating a full 360 degrees each time the piston goes from TDC to BDC and back. And in a car capable of a redline around 7500rpm, the engine is completing this reciprocation around 125 times a second.

Different Types of Car Engine Timing

There are two kinds of car engine timing: cam timing and ignition timing. The cam timing regulates the valves and pistons, and the entire process is controlled by the timing chain or belt. If the timing is off, damage can occur. In some engines, called “interference engines,” the consequences can be especially bad. With this type of engine, the engine valves and pistons occupy the same space in the cylinder, but at separate times. Since the intervals between the time when the piston owns the space, and the time when the valve owns the space is far less than a second, you can imagine the consequences if the timing is off. You could end up having to have your engine rebuilt, or even replaced.

To hold this extremely precise series of events together, a timing belt, chain, or ger is used, connecting vital components of the engine together to keep everything coordinated. A timing belt for example is a thick, toothed belt that runs around the camshaft sprockets, the water pump pulley, and the crankshaft sprocket, therefore rotating in time with the crankshaft at the bottom of the engine block.

This timing system is synchronized with ignition by alignment markers or timing marks on the valve cover, camshaft, and crank sprockets. Using small dashes, numbers or lobes situated on the sprockets, the timing system can be aligned so that – once the engine is fired up – the rotation of the timing belt will synchronize the camshafts opening their respective valves to the crankshafts reciprocation of the pistons, along with the timing of the ignition. The manufacturer places these timing marks to set a crankshaft angle (within its 360-degree scope) for ignition to occur.

A timing mark on a cam sprocket properly aligned with its respective valve cover mark

Valve Timing Basics

Valve timing in its simplest form is controlled by the lobe profiles on the camshafts, with the aim to open the valves within the engine for the exact amount of time to get as much air/fuel mixture in and then exhaust gases out for each engine cycle, maximizing the engine’s efficiency. The lobes control the lift (the amount the valve opens by) and the duration (the time it stays open for), with engine technology in the nineties making the jump to variable valve timing to make the camshaft as versatile as possible.

Timing Adjustment Basics

Now that you know what timing is, I can tell you about the basics on how to adjust and set it on your engine. Timing is different on every engine, so it’s a good idea to have a good service manual handy to talk about the details in your engine. Newer engines adjust the timing themselves, so if your sensors are all functioning as they should, you will not have to do any tinkering with timing. In fact, you usually cannot unless you remap your ignition computer’s chip or buy an aftermarket performance chip that has a different timing map flashed into it. Be careful because the wrong chip can not only make your car run badly but can also throw error codes and bring on the dreaded Check Engine Light.

If you are cool enough to have an older school car or truck with a distributor that you can put your hands on, adjusting the timing is as simple as giving the distributor a twist. You will need a timing light. With the light wired up per the instructions and the engine running, point the light at the main pulley that comes off the crankshaft. This pulley has a notch or mark on it. On an engine timed to zero degrees advance, also known as Top Dead Center, that mark will appear to flash with the light pointed at it. If you loosen the distributor and turn it slightly, you will see that mark move to the left or right. Turn the distributor too much and the mark will leave entirely. You can also shut off the engine in this way. On most crank pulleys, there is another mark. This is the mark you aim for, usually somewhere between 3-5 degrees before Top Dead Center. All you do is turn the distributor until that timing mark is flashing at the right spot every time. Once it is set, tighten the distributor so it will not turn on its own, and you are good!

Finally

The most important thing is that the spark happens on time. If it does not, you can end up with choppy idle, no power, or an engine that just will not work. You should never ignore engine timing problems, since if the timing is off, serious engine problems can be the result.

Although the chances of car engine timing ever going wrong are slim, it is always worth making sure that the belt or chain on your car is in undamaged shape. Although it may seem like a simple check, it could potentially save your high mileage daily from the scrapheap. Once your basic timing is in check, the door is then opened to consider altering valve and ignition timing, fine-tuning your engine to maximize efficiency and power. As they say, timing is everything!