NOTE The piston and pin (1) are matched and are not replaced separately.  Replace as an assembly only.  The three ring assemblies (2) each consisting of an outer ring and an inner ring (3) are supplied in the form of a piston ring kit and should be replaced as a kit set. (2) Remove four cap screws (5) and lock washers (6); remove cylinder head (4), head gasket (7), valve assembly (8) and valve gasket (15) from cylinder (16). (3) To disassemble valve assembly (8), remove cotter pin (10), castle nut and separate upper guard from valve seat. NOTE The lentoid springs (11), valve ring (12), lentoid springs (13), valve ring (14), and cotter pin (10) are supplied in the form of valve repair kit and shall be replaced as such. (4) Remove lentoid springs (11), valve ring (12), separate and remove lower guard, remove lentoid springs (13), and valve ring (14) from valve seat. (5) The center bolt is secured in valve seat with dowel pin peened over and neither should be removed. b. Cleaning.  Refer to paragraph 6-3.a for general cleaning instructions. (1) Remove caked grease or dirt with a non- metallic brush after immersing part in solvent.  Scrape carbon, and old gasket material from affected surfaces. (2) Clean parts with care.  Do not mar or scratch contact or seating surfaces. Exhaust valve components should not be wire brushed. c. Inspection.  Refer to paragraph 6-3.b for general inspection instructions. (1) Parts with dimensions listed in Table 6-1, Table of Limits, shall be measured to ascertain acceptability for repair or replacement and assembly. d. Repair or Replacement.  Refer to paragraph 6- 3.c for general repair or replacement instructions. (1) Replace all gaskets removed during disassembly. Do not remove any more material than is necessary to completely remove the glaze.  Clean the  cylinders  in accordance with CLEANING procedures. (2) Remove glaze from cylinder walls with portable cylinder hone (using 280 to 400 grit stones).  a glaze buffer, or a crocus cloth, depending on condition of cylinder walls. e. Assembly.  To assemble the third stage cylinder and piston group, proceed as follows: NOTE A repair kit consisting of lentoid springs ( I I ) valve ring (12), lentoid springs (13), valve ring (14), and cotter pin (10) is available.  At overhaul replace these parts as a set.  Assemble lentoid springs (11 and 13) as illustrated in Figure 6-8. (1) At overhaul of intake-exhaust valve assembly (8), use available repair kit (9). Assemble valve ring (14) and lentoid springs (13) in valve seat and assemble lower guard plate.  Assemble valve ring (12), lentoid springs (11), upper guard and castle nut.  Secure nut on center bolt with cotter pin (10). (2) Assemble valve gasket (15), valve assembly (8). head gasket (7), and cylinder heat (4) to cylinder (16).  Secure head to cylinder with lock washers (6) and cap screws (5).  Torque cap screws (5) to 45 pounds foot (Table 6-2). NOTE The piston ring assemblies (2) are available in a ring kit and are to be replaced as a set. (3) Assemble inner and outer rings of ring assemblies (3) in grooves on piston (1). Coat the rings with clean compressor oil to aid in assembly. 6-20. Fourth Stage Head and Cylinder Group (See Figure 8-17).  The following paragraphs contain disassembly, cleaning, inspection, repair or replacement, and assembly instructions for the fourth stage head and cylinder group. 6-27