As your engine runs, the intake valves need to open up to allow air into the engine. They remain closed while the air and fuel is compressed and ignited, powering the piston. Then the exhaust valves open to release the exhaust. This all has to be timed very precisely. It is the job of the timing belt or timing chain to make sure all of this is synced up properly.
Timing belts are made of a very tough compound that can last for a long time. Timing chains are made of metal and last for a very long time as well. If your vehicle has a timing belt, your owner’s manual has a schedule for replacing the belt. If your vehicle has a timing chain, there may not be a specified schedule for replacing it, but that doesn’t mean that the timing chain system is indestructible and never needs attention.
For example, the chain runs on sprockets on the crankshaft and the camshafts. A broken tooth on a sprocket can cause the chain to slip a little. When timing is off a little your engine will not run as smoothly. When timing is off enough, your engine won’t run at all and could even be severely damaged. There is also a tensioner that keeps appropriate pressure on the timing chain. This keeps the chain tight while allowing it to absorb pulsations from the engine. The tensioner can wear out. There are also guide rails that keep the chain on the proper path that can become worn.
The bottom line is that at some time, one or more of the timing chain system components will become worn to the point that they are no longer performing within specification. Your service advisor can help you with recommendations for when timing chain components should be replaced on your vehicle and have it inspected for signs of timing chain system wear.
Since timing chains are lubricated by engine oil, staying on top of your regular oil changes is very important to long life. Always use a high quality oil filter and oil of the recommended type and grade.