by Jacks1986Lebaron » Mon Jun 22, 2009 10:45 pm
Found this.....it may help??
A camshaft is commonly used to operate poppet valves in a piston engine. A cylindrical rod is situated in the cylinder block or cylinder head which has oblong lobes or cams which push the intake and exhaust valves. This force is applied on the valve directly or through an intermediate mechanism such as a rocker arm, lifter (cam follower) and push rods are used to press against the valve for movement. Each valve utilizes a spring which will return the valve to its original position (closed) after the force is removed. If a valve spring has broken or a cam lobe has worn down it will cause the engine to misfire and run rough because it causes the engine to lose compression. You might say" wouldn't either of these conditions show up in a compression test?" and the answer is not always. The problem with a compression test is that it is performed at engine cranking speed. If you have a worn camshaft it will show up only when the engine is running. In some conditions a broken valve spring can effect different aspects for example: If just one coil of spring breaks off, the spring can still close the valve but only at low RPM's, causing a high RPM engine misfire if the spring breaks somewhere in the middle it will affect both idle and power conditions. To test for this condition, remove ignition coil connector or ignition system or fuel pump fuse to disable power to the ignition or fuel system. Remove the valve covers to gain access to visually inspect the valve train. Have a helper crank the engine over while you watch the rocker arms or cam lobes, make sure they are all going up and down the same amount, if one or more lobes are traveling less than the others you have a flattened cam lob and the camshaft needs to be replaced. Inspect the condition of the valve springs, use a flashlight and small mirror to aid in the inspection. If a broken valve spring is discovered it will need to be replaced to correct the problem.