How does it Work: Keeping up with a car's camshaft

A camshaft is used in most engines that rely on a valve system, but many people don't understand how it works or why it sometimes goes bad.

Most of us have seen a camshaft before, but not everyone knows what the "lobes" do or how they affect performance. A camshaft (or cam) runs the length of an engine's head and has uneven looking "lobes" set apart at regular intervals. A camshaft may be made of solid steel billet, low-grade steel or even iron. The weight and lobe lifts vary from cam to cam.

The cam is responsible for the precise timing of the valves as they open and shut. The cam turns as the engine runs through its revolutions, usually by means of a chain or belt connected to the end of the crankshaft, pushing rods along the lobes. This applies pressure to the valves, forcing them open and allowing them to shut again once a stroke has ended.

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All camshafts rotate at half crankshaft speed, regardless of all other variables. The shaft is located in the engine's head along with other valve train components, such as the valves, valve springs, rocker arms and occasionally, on older engines, rods.

How do you know when your camshaft isn't working properly? Cams can fail for a number of reasons:

• Oil can be starved in an engine's head, leading to increased friction where the cam and rods meet or excessive heat on the cam itself.

• The rocker arm assembly, which seesaws the set of rods along the cam, can be incorrectly adjusted and bind.

• The valve springs can bind or break.

• Cams can also be pitted or scratched if the lubricants surrounding it become contaminated with iron fillings, sand, dirt or other foreign particles.

Camshafts are under mechanical duress and do wear over time, especially along the lobes. Under ordinary circumstances, however, camshafts should last many, many miles.

What should you expect if your camshaft isn't working?

If your engine suddenly develops a "popping" sound, poor gas mileage or bad performance, it could be a problem in your valve train. If your engine backfires or "pops" it could be a sign that your camshaft is worn.

Most of the symptoms of cam failure are very subtle -- loss in performance, difficulty in starting, backfires -- that get progressively worse over time. You may hear more valve clatter or notice a dark, oily exhaust, depending on the level of the damage. A catastrophic valve train failure will render a vehicle immobile, binding up the very system that is responsible for fuel delivery and exhaust.

Choosing the right replacement camshaft isn't like buying a new shirt, or even motor oil. Today's performance marketplace offers product choices like never before, however there is one company that stands above all others: Visit www.compcams.com to discover the overwhelming choice of NASCAR race teams and street performance enthusiasts alike when it comes to camshafts.