Timing Belts Demystified

In order to run correctly, a car engine relies upon a precisely timed series of events. These events must occur in the proper sequence and at precisely the right times. The events include opening and closing of intake and exhaust valves, delivery of fuel and air to each cylinder at the proper times, and generation and delivery of ignition voltage or “spark” to each cylinder when needed.

In nearly all engines, some of the work which is required to accomplish these tasks is derived from a single shaft within the engine that is called the crankshaft. As the crankshaft rotates, it drives one or more smaller shafts, called camshafts. These camshafts are what actually control the opening and closing of intake and exhaust valves for each cylinder in the engine.

This is where the timing belt comes in. Each camshaft is connected to a pulley, and the camshaft pulleys are connected to the crankshaft (which also has a pulley) via one or more timing belts. (see illustration).

Timing belts are made of materials not too unlike the tires on your car, and they wear out in a similar manner. Generally speaking, most car manufacturers recommend replacement of timing belts on their engines at 60,000 to 70,000 mile intervals.

Having a broken timing belt is no fun at all. With some engines, a broken timing belt will simply leave you stranded until the belt is replaced, with no further harm and minimal expense. However, some car engines are designed in such a way that if a timing belt should break during a period in which any of the above mentioned intake or exhaust valves are open on any of the cylinders, there is a strong likelihood that these valves will be bent or broken due to coming in contact with pistons. In this case, much more work is required to repair the engine, and it can get to be quite expensive. In short, its probably not a good idea to gamble with your timing belt. Have it checked and/or replaced at the proper intervals as recommended by the manufacturer of your car or truck.

For the home mechanic, you can also inspect the timing belt yourself. The first thing to do is to obtain a service manual for your vehicle. The service manual will usually show step-by-step procedures regarding the inspection and replacement of the timing belt, often with accurate illustrations to help guide you with the process. Online service manuals for nearly all makes and models of consumer vehicles are now available.

Generally, you will need to remove an inspection cover of some type in order to visually inspect the timing belt. You can then look closely at the belt for cracks, wear marks, missing teeth, etc. and check for proper tension. If replacement is necessary, you can do the job yourself if you have a) The service manual for your vehicle, b) A clean, well lighted place in which to work on the vehicle, and c) Proper tools – i.e. socket wrenches, combination wrenches, screwdrivers, pliers, shop rags, etc.

Some timing belt replacement jobs are quite complicated and are best done by a professional repair techician. This is one area on your vehicle where you should not compromise – your comfort, safety, and your pocketbook  could depend on it.  In other words, if you don’t feel absolutely confident that you can replace your own timing belt then don’t. Have the job done by a reputable repair shop or dealer.