Inside Harley's Milwaukee-Eight Motor

CHECKING OUT THEIR 4-VALVE HEADS

- John Sullivan

THE MILWAUKEE-EIGHT’S COMBUSTION CHAMBER IS A 4-VALVE DESIGN. THIS IS A MAJOR IMPROVEMENT OVER THE TWIN-CAM’S 2-VALVE SYSTEM. HAVING TWO SMALLER INTAKE VALVES IN EACH COMBUSTION CHAMBER IMPROVES THE MOTOR’S LOW RPM PORT VELOCITY; YET THEIR OVERALL SURFACE AREA IS GREATER THAN THE TWIN-CAM’S SINGLE VALVES, WHICH IMPROVES THE MOTOR’S CYLINDER FILL RATE.

ALONG WITH THE SMALLER VALVE SPRINGS, THE TOP OF THE NEW CYLINDER HEADS HAS FOUR RAISED MOUNTING STANDS THAT THE ROCKER ARMS ARE BOLTED TO.