The timing belt (or cam belt) and timing chain are a part of your car's engine's timing and is what synchronizes all of the engine's operations, creating the timing intervals the engine runs from. Nearly all gasoline-powered and many diesel-powered combustion engines use a timing belt or a timing chain to accomplish this, depending on construction.
Whether a belt or a chain, the timing of the engine will be determined by its rotation. The main difference between a belt and a chain is is construction, with a belt being made of rubber and other components while a timing chain will be a metal chain running around gears. Each has its own advantages and disadvantages, but most of today's passenger vehicles now use a timing belt (or cam belt) rather than a chain.
How the Timing Belt or Chain Works
Whatever the choice, the timing belt or chain will be powered by the crankshaft, which will have a pulley or gear at the front of the engine, at bottom. Remember that engine directions are relative to the engine itself, not the configuration of the engine's mounting in the vehicle.
From the bottom of the engine, the belt or chain will stretch upwards to the camshaft pulley(s) at the top of the engine, on the engine head(s). There will be one pulley if it is a single overhead, inline camshaft configuration or more than one if it is a V-style or multiple overhead camshaft configuration. In between the crank and camshafts, the belt or chain will often power other critical engine components like the water pump (for engine cooling) and sometimes the oil and/or fuel pump, depending on engine configuration. Often, the tightness of the chain or belt will be regulated by a tensioner pulley as well ? a small pulley that pushes or pulls on the chain/belt with a tension spring to provide the leverage.
The timing belt or chain creates a specific time interval for each turn of the crankshaft versus the time interval for the turning of the camshaft(s). This, in turn, dictates when the valves open and close to inject or exhaust air and fuel into the combustion chambers (cylinders). It is critical that the belt or chain's turn be in perfect time for the engine to run at optimum.
Why a Chain? Why a Belt?
Why a chain (and why not):
- The timing chain has one distinct advantage over a timing belt: durability.
- The timing chain rarely goes out of service, so it remains in perfect time, with no replacement interval or wear and tear under normal operations.
- In most engines, the timing chain will last the lifetime of the engine itself.
- It's chief drawbacks are noise, weight, and expense.
- Timing chains are relatively noisy as they clank around the gears they turn, are made of heavy metal, and are expensive to build and install.
Why a belt (and why not):
- Timing belts, on the other hand, are fairly cheap to construct, light weight, and operate quietly.
- They require regular replacement, however, and can fail if not properly cared for or installed.
- Most vehicles require a timing belt change every 60,000 to 100,000 miles.