TM 10-3930-660-34 3-7. CYLINDER HEAD ASSEMBLY - REPLACE/REPAIR  (Cont’d) 8. CHECK SPRING FORCE USING A VALVE SPRING TESTER. Description ...................................... Specification Test force   ......................................65.0 - 72.2 lb. Length under test force  ........................... 1.94 in. Free length after test  ............................... 2.19 in. Spring must not be bent more than  ......................................... 0.039 in. REPAIR 1. GRIND THE VALVES. a. Grind valves to proper face angle. Valve Face Angle Intake: 300 Exhaust: 450 b. Measure valve rim thickness. Limit Minimum (A): 0.031 inch If rim thickness is less than 0.031 inch after grinding, replace valve. c. Mark valves again respective to their location in the cylinder head. 2. MACHINE VALVE GUIDE BORES. If valve guide bores are scratched,  scored, burned, or worn, the guide bores must be machined and service valve guides installed. 3-41