A cam pulley is part of the timing system in an engine used to control the rate of rotation of the camshaft, the component that controls the poppet valves responsible for air intake and exhaust in the cylinders. The cam pulley articulates with the timing chain to rotate the camshaft in synchronicity with the crankshaft. This vehicle component is typically checked during a timing belt replacement to determine if it needs repair or replacement, and may be swapped out in high performance vehicles that see substantial engine wear.
The camshaft controls when the cylinders open and close. The speed of operation determines the best engine timing, and car manufacturers use a number of tools to control the timing so a car will operate optimally at a range of speeds. Some cars are tuned for high performance and may be rough at low speeds because the valves are open longer, while others have difficulty running at high speeds because the intake needs aren't met.
An adjustable cam pulley creates more room for maneuvering and can be seen on some high performance cars with very high demands. Other cars use options like dual camshafts to adjust the timing as the driver accelerates and the engine timing needs to change to compensate for the increased speed. Adjustable pulleys are available as replacements for some vehicle modifications and some cars may come with them by default from the manufacturer, or on special order from a customer.
During a timing belt change, it is important to make sure the cam pulley is properly adjusted. It usually has markings to line up with the other components of the engine. When the mechanic takes the old timing belt or chain off and places the new one, she can line up the markings to ensure the engine will have the proper timing. This also provides a chance to check for wear and other problems that might damage the engine or interfere with the timing.
Manufacturers provide a range of cam pulley options for their vehicles. It may be possible to use an aftermarket part rather than one produced by the manufacturer. This option can be preferable for mechanics who want to cut costs or install specialty modifications that are not available from the auto maker. Drivers should be aware that such parts may void a warranty, and if a problem arises, the dealer may not be able to fix it.