A MAINTENANCE TECHNICIAN WAS INSTALLING A GREASE PUMP MOTOR. THE TECH MISTAKENLY HOOKED UP THE AIR HOSE TO THE MOTOR BEFORE HE HAD COMPLETED INSTALLATION. WHILE TIGHTENING A MOUNTING BOLT, THE TECH INADVERTENLY BUMPED AN AIR VALVE WHICH ACUTATED THE AIR MOTOR SHAFT. THE TECH'S RIGHT FOREARM WAS CAUGHT BETWEEN THE AIR MTR SHAFT & THE PUMP SHAFT.