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The camshaft is spun-up on the balancer similar to any other rotating shaft.
Example of a camshaft out of balance. Notice that the left side of the camshaft is 1.2 in./oz. out of balance and the right is 1.67 in./oz. out. Also note that the unbalanced units are not opposed to each other. This will cause the shaft to combine the out-of-balance forces, causing a bending moment as opposed to a canceling effect.
In this example the camshaft is running at 4,000 rpm (half of the 8,000 rpm crankshaft speed). The left side of the camshaft is generating a force of 34.3 pounds and the right side is 47.6 pounds, and both are hammering at 66+ times per second. This may be enough to cause the camshaft to become excited and set up a vibration pattern that will motivate the roller lifter to bounce on the surface of the lobe. Ultimately, the valve will respond to all of this activity and most likely this will cause the valve to follow a path that is not equal to the designed cam lobe profile. This may also cause the valve spring to become excited, generating an inconsistent travel pattern commonly known as valve spring float.
The corrected report shows that the out-of-balance has been minimized and the residual unbalance is in-couple (meaning that the forces are opposed to cancel each other).
If imbalance is excessive, it may be necessary to add one or two external weights. This approach of course, is dictated by the cam design, where space permits, such as on a 4.6L Ford. The example shown here features two counterweights.
External counterweights are two-piece and clamp onto the shaft.
Any camshaft, ranging from the cheapest cast OE to the most exotic aftermarket grind, may feature an imbalance condition, from mild to wild. It doesn’t hurt to check.
Correcting a camshaft imbalance condition can result in a more efficient (optimized) valvetrain operation.
Tags: BALANCING, CAMSHAFT, CWT
