ALT-3 What is a Timing Belt
Let's start with a little background information here. Your engine operates through 4 cycles to keep it running. That's why it is called a 4-cycle engine. The timing belt, is what keeps these 'strokes' happening at the right time.
Here is what happens when the engine is in each cycle1) IntakeThis is when the air and fuel is drawn into the cylinder. As the piston comes down, the intake valve opens, and air/fuel mixture is sucked into the engine, like a straw. When the piston reaches the bottom of the cylinder, the intake valve closes and the compression stroke begins.
2) CompressionWith the intake stroke completed and the valve closed, the rotating of the crankshaft begins to push the piston back up to the top of the cylinder to compress the air/fuel mixture that was sucked in the cylinder. More compression usually means more power. Cylinder compression is usually well over 100 PSI.
3) PowerYou guessed it, this is when the compressed fuel mixture is ignited, while the valves are still closed. Spark happens right when the piston is at top dead center to make the resulting explosion as violent as possible. This is to help ensure complete combustion (more power, less emmissions) When the piston is forced down from the explosion is when the cylinder makes power, hence the name.
4) ExhaustOnce the power stroke is over and the piston is at the bottom of the cylinder again, the exhaust valve is opened. The piston comes back up to expell the burned exhaust gasses from the engine. As the piston is coming up on an open valve, it needs tu close before the piston hits it. Once the piston reaches the top again, the valve 'by thin margins' closes, and the intake valve begins to open to start the process over again.
Each cylinder is considered an engine, and this happens, very fast, in each cylinder. So if you have a 6 cylinder, that is actually 6 different engines.
If the timing belt breaks, the valves stop moving, but the crank will still rotate and move the pistons up and down. Some valves are still stuck open when this happens. When the piston comes up (it eventually winds down and stops, of course) it hits the valve and bends it. Then the head needs to come off the engine.
The major thing you can do to check the condition of the timing belt in your car is to line up the timing mark on the crank, and see how close the camshaft is. Another quick and effective way is with the use of a vaccuum guage. There will be a lower than normal reading if there are no vaccuum leaks. A vaccuum guage is inexpensive and indespensible. It will let you know the condition on your engine is very short order.Timing belt changing intervals vary by manufacturer and engine size. Most newer cars have an interval of 100,000 miles, but there are still some that require the belt to be changed around 50,000 miles too, so check with the manufacturer.
If the water pump on your engine is timing belt driven, they are designed to wear out at the same time, so change it too, or you will be doing it again in about a month.
Hope this helps!
