TM  10-3930-643-34 GENERAL  SUPPORT  ENGINE,  FUEL,  EXHAUST  AND  COOLING  MAINTENANCE. 13-2. Cylinder Head Assembly with Valves. (Sheet 2 of 6) DISASSEMBLY 1. 2. 3. Inspect 12 guides (1) head (2). Replace if or excessively worn. with a .374 reamer to correct  mushrooming. in  cylinder burned,  cracked Ream  guides remove burrs or I.D. of valve guides must not be more than 0.3750 inches. Measure I.D. of 12 valve guides (1) at top, middle and bottom with a ball gage. Replace valve guides only if worn beyond limits. Using valve guide remover tool, remove any worn valve guides (1). Go to sheet 3 13-9