A lot of people are letting their automotive maintenance slip a little due to the economy. While this can save some money in the short term, there are certain items which can really cost a lot of money if ignored too long. One such item is the engine timing belt.
What is a timing belt?
The timing belt is a neoprene belt that connects the camshaft to the crankshaft. It allows the internal functions of the engine to occur. As the belt turns the camshaft, the engine valves open and close. The valves allow gasoline to enter the combustion chamber and then they allow the exhaust gases to exit. The camshaft has machined "cams" on it that push to open the valves. The camshaft rotates, (via the timing belt), which opens, then closes, the valves. Without the cam pushing, the valve cannot open and an open valve cannot close. The belt usually has a smooth side and a side with notched teeth. Each tooth meshes into a gear on the camshaft and the crankshaft.
Why should I care about the timing belt?
The timing belt is made of neoprene and it operates in a fairly hostile environment. It is subjected to high heat and rotates at speeds up to about 4000 revolutions per minute. It turns at half of the speed of the engine. Even idling at a traffic light, the belt will be turning at about 500 or 600 RPM. When the engine is working hard, the belt is under a great deal of stress. This may cause the belt to stretch or wear. In extreme circumstances, the belt can actually break. Most automobile manufacturers recommend that owners should replace the timing belt at a regular interval, perhaps every 50,000 to 70,000 miles. You can look up your car for it's timing belt replacement chart. The belt must be replaced before it fails or potentially severe engine damage will result.
What can happen if the timing belt breaks?
If a timing belt breaks, the camshaft will no longer turn. This means that the valves cannot open to allow gasoline into the engine, nor can exhaust gases exit. That in itself is not a big problem; the engine will not continue to operate unless the timing belt is replaced. The problem is that many valves are open inside the engine at any one time. Without the timing belt turning the camshaft, the open valves stop in the open position. Most engines are known as "interference valve" designs. This means that an open valve can interfere with the engine's pistons. This is a way of saying that the pistons can hit the open valves.
Normally, they can't because the timing belt closes the valves before the piston can ever come in contact with the valve. With a broken timing belt, however, the valves remain open and they can be hit by the pistons. At any one time, some of the valves will be closed. These valves can't be affected by the pistons. Some valves may be partially open. These can either be struck by the piston or there will be a close miss. Other valves will be open farther. These valves can be struck by the pistons, perhaps struck very hard. Remember that the engine can't run with a broken timing belt. It will, however, continue to rotate while the inertia allows it to. If the engine is rotating at 3000 RPM, and the timing belt suddenly breaks, the engine could turn for a few seconds until it completely stops. At this engine speed, there are 50 revolutions every second. Each one of them will cause some of the valves to be hit by the pistons. Valves were not designed to take the impact. They are very strong parts made of steel, but they are prone to damage if hit by the piston. The shafts of the valves may bend or even break. In some cases, the valve is perhaps too strong. Rarely, the piston will be damaged as it hits a valve dead on. The valve may punch a hole in the piston. Regardless of the damage caused by the valves contacting the pistons, the engine will be severely affected or even destroyed. The cascading effects of the timing belt breakage can be terrible. They are also avoidable.
Get an older belt replaced!
If your car has between 50 and 70 thousand miles on it, and the belt has never been replaced, it is time to get it done. You do not want the part to fail with the catastrophic effects that can result. If you have purchased a used car with more miles, and you do not know the service history, you should replace the timing belt as well. The timing belt will rarely exhibit signs of imminent failure. In fact, inspection of the timing belt requires practically as much service time as a complete replacement. Unfortunately, the cost of a timing belt replacement is not cheap. Many engine parts must be removed by the mechanic. When the timing belt is being replaced, it gives your mechanic a chance to change some other service items. Usually all of the engine drive belts have to be removed first. All of theses, (1, 2 or 3), can be replaced with new units for a low cost. Many mechanics will take the opportunity to replace the front engine oil seal. This $10 part cannot be replaced with the timing belt in place. Other components can be fully inspected as they are removed. These include the water pump, alternator and other component parts. Any that need to be replaced can be done with little additional cost to the timing belt replacement cost. All of the service costs will add up to a fairly high repair bill, however. Even so, the preventative repair will potentially save thousands of dollars if a timing belt is replaced before it has the chance to break.