A majority of the vehicles on the road today with either diesel or petrol engines in them are only able to mechanically work if they are timed properly. Engine timing on a vast majority of today's vehicles is either done by the use of a synthetic rubber belt or a steel timing chain.
The importance of engine timing is not easy to explain but we will give it a shot to make it easy to understand. Using a four cylinder single overhead cam engine as an example, there are two main rotating assemblies on the engine itself, one being the crankshaft and the other being the cam shaft. The crankshaft has a singular purpose to rotate forcing the piston rods up and down in the cylinder bores throughout the engines four stroke cycles. The camshaft is responsible for opening and closing the valves inside of the head at designated intervals to either allow air into the cylinders or to remove exhaust after the combustion event.
If these two components are not synchronised properly the vehicle, by design, cannot run. When the engines number one cylinder is at top dead centre (the highest point of its travel) there will be a timing mark on the crank pulley or gear which must align with the timing mark built into the engine. When a vehicle is at top dead centre on the number one cylinder, the valves in the head for that cylinder must be in a fully closed state to allow for either the compression stroke or the combustion stroke of the engine on that cylinder. This timing is normally facilitated with the use of another timing mark being present on the camshaft sprocket which would then align with another timing mark on the engine itself to assure everything is properly in line.
If the timing is off by as little as one tooth the vehicle may be able to fire and run but it will not perform as intended, and many vehicles will not even attempt to run if the timing is not perfect. A qualified mechanic would be able to look at the timing components and identify the timing marks to ensure the engine is timed properly before trying to fire it up.
Some vehicles are classed as what is known as an interference engine. If one of these engines has the timing miss set even by as little as a tooth it can cause the valves to open at the wrong time allowing them to actually make contact with the pistons as they are at the top of their travel. If this happens it is common for them to bend the valves which would require removing the cylinder head and replacing the valves before the engine can be fired up again. This is not an easy process on many of today's vehicles.
It is important to make sure the time is set by an experienced technician in order to safeguard your investment. While there are manuals the layman can buy which will guide them through the process of timing an engine. The chance for error outweighs the savings you may make by performing the process yourself so it is best left to the professionals to make sure the job is done right the first time.
