I get asked this question often. What is a timing belt, and why do I need to have it changed?
The simple answer, the timing belt has teeth on the inside of the belt that keeps the engine in sync, or in time. There are essentially 2 halves of an engine, an upper and a lower half.
The lower or bottom side of the engine has the crankshaft, connecting rods and pistons, it is known as the rotating assembly because the pistons are connected to the crankshaft.
As the explosions takes place from the fuel being ignited in the cylinder, the pistons are forced downward causing the crankshaft to rotate. The crankshaft has teeth on a gear on the front that the timing belt rides on. This rotation causes the belt to move and turn the upper half of the engine that contains the camshaft, or multiple camshafts, valves and lifters. There’s also a toothed gear attached. The camshaft pushes down on the valves against the springs to make them open and close. This lets air and fuel in on the intake side, and also lets the exhaust gases out through the exhaust side. All this has to take place at the exact time for the engine to run properly, and stay in time.
When the belt, which is made out of a rubber material, ages, the teeth start to crack on the inside and can shear off or brake. This break in the belt will allow the lower end of the engine to turn, but the belt stops turning, causing the upper part of the engine to stop moving.
When this happens some of the valves are usually open so when the piston comes up it hits the valves and they get bent. Most cars today with a timing belt have what’s called an interference engine. Which means not enough clearance between the valves and pistons when the timing belt brakes resulting in the pistons hitting the valves while there open and they bend. This causes engine failure and will require engine disassembly. Replacing the timing belt is a much less costly service and will prevent the engine repairs from being needed.
The timing belt also turns the water pump in a lot of engines, it is best practice to replace preventively at the same time along with flushing the cooling system with new antifreeze. You should also replace the tensioner and idler pulley’s to make the job complete. Any time you can access harder to reach areas, it is better to replace some things preventively.
I hope this information helps you understand the importance of changing your timing belt in your car's engine.