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  BASIC CAMSHAFT KNOWLEDGE

 Tech Area

A camshaft actuates (opens and closes) the engine valves. Rotating at one-half the crankshaft or engine speed, the camshaft is responsible for the correct timing (with respect to piston location) of air/fuel mixture and exhaust gas flow in and out of each cylinder.

In today's cars, the camshaft is located in either the engine block - an overhead valve design (OHV), or in the cylinder head in the overhead cam layout (OHC). Some engines even employ a double overhead cam (DOHC) design in which there are two camshafts - one for the intake valves and the other for the exhaust.

Although there are differences in physical construction, the operating principle is the same in either case. As the camshaft rotates, the lobe pushes up on a lifter or down on the lash or valve cap. In an OHV engine, a pushrod is seated in the lifter and acts as an intermediate link between the lifter and rocker arm.

In both engine designs, the rocker arm or lash cap compresses the valve spring to open the valve. As the cam continues to rotate, the force is relieved and the valve closes.Usually, the contour on both sides of the lobe is the same (the contour, or profile, controls the acceleration of the valve). However, if it differs from side to side, the camshaft is said to be asymmetric. The Ford 2300cc engine has asymmetric lobes. If the intake and exhaust lobes have different profiles, the camshaft is referred to as dual pattern design. Some of the so-called "mileage" camshafts are dual pattern.

The measurement that indicates the amount, in inches, that the cam opens a valve is the lift. There are two types of lift - cam lift and valve lift. Cam lift is the distance the lifter is raised by the cam lobe. Valve lift is the amount of valve spring compression (how much the valve opens) due on the mechanical advantage of the rocker arm. (OHC engines that do not use cam followers or rocker arms measure valve lift directly by cam lift. In these engines, cam lift and valve lift are identical.)

1. Basic Camshaft Knowledge
2. Helpful Tips
3. Camshaft Tuning Tips
4. Important Notes