Two employees (mechanic and operator) were changing the wheels on a landfill compactor. The operator was operating a wheel loader and lifted a large metal compactor wheel off the ground to be installed on the compactor. The mechanic was signaling directions to the operator to align and set the wheel in place. While signaling and moving the wheel onto the machine, the wheel shifted on the loader forks and pinned the mechanic between the forks and the wheel. The mechanic suffered a fractured rib, hip and vertebrae.