Timing belts (typical example) can be quite confusing. First, not every engine has one. Some engines use gear drives or timing chains, which do not normally require maintenance. Others use belts and like any piece of rubber, the timing belt must be replaced in time. The best way to know if a vehicle has a timing belt is to refer to the owner's manual or ask a trusted professional.
The recommended replacement interval also varies, depending on several factors. Primarily the engine design and age determines when the belt should be replaced.
There are interference and non-interference type engines. Interference means the engine valves and pistons occupy the same place, just not at the same time. On these engines, a broken or slipped belt often means the valves will hit the pistons. When this happens the result is normally a ruined engine.
On non-interference engines the valves will not hit the pistons if the belt slips or is broken. While not as disastrous, the engine will stop running. Timing belts are normally recommended between 60,000 and 105,000 miles. The interference type engines are closer to the lower end and the non-interference type closer to the high end.
It is also extremely important to remember that time is a major factor. Most manufacturers recommend seven years as the maximum life of the timing belt. For instance, even if the engine only has 30,000 miles, but is seven years old, the belt should be replaced. Below is a belt eight years old, but with only 30,000 miles of service.
Replacing a timing belt normally involves a good deal of effort. Because of this, there are several other components in near proximity, that might also be replaced. For instance, the water pump, if under the timing cover, can be replaced at a greatly reduced price. Because water pumps wear out, many people see the wisdom of replacing it when the belt is replaced. Not replacing these components often results in an expensive re-do of the timing belt job. Doing a complete job is far less expensive and less dangerous than having to do the job over.
There are companies that merely replace the belt alone. While this may seem like a savings, it can spell disaster. For instance, suppose the water pump fails ten-thousand miles after the belt is replaced. Not only does this involve another full disassembly, the pump can actually cause the belt to be thrown off.
Another problem is a seal that starts to leak after belt replacement. The seal might have been replaced for a minimum cost while the belt was off. Now many of the same components must again be removed. Worse, the oil from the leaking seal can ruin a new belt. Remember, you never get more than you pay for.
