WHAT’S SHAKIN’?

The terrible truth is that no matter how finely you add or subtract balance weights from your crankshaft using a high-tech balancing machine, a rotating counterweight can never cancel the shaking force of a piston moving back and forth in a straight line. The only way a single can be balanced is by generating an equal and opposite in-line shaking force.

Here’s why. Let’s start with a single-cylinder engine whose rotating parts—the crankpin, its bearing, and the big end of the connecting rod—have all been 100 percent balanced by rotating counterweights attached to the crankshaft at 180 degrees to the crankpin. All that’s left now is the