a. Disassembly.  Disassemble the fourth stage head and cylinder group only to the extent necessary to repair or replace a defective part or parts. (1) Remove eight cap screws (2), lock washers (3), remove cylinder head (1), head gasket (4), valve assembly (5), and valve gasket (11). (2) To disassemble valve assembly (5), separate and remove lower guard and remove lentoid springs (7) and valve ring (8).  Separate and remove upper guard from valve seat and remove the closing spring (9) and valve disc (i 0). (3) Pipe plug (12) need not be removed from cylinder (15).  The cylinder liner (14) is a press fit in cylinder (15).  To remove, use an arbor press or other suitable means, and press liner out of cylinder in the direction of the head (toward top of cylinder). 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, grease, and old gasket material from affected surfaces. (2) Clean cylinder with care.  Do not mar or scratch contact or seating surfaces. 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. (2) All parts or subassemblies which do not meet minimum acceptable standards shall be repaired or replaced with a like serviceable item. 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 breaker, or crocus cloth, depending on condition of cylinder walls. e. Assembly.  To assemble the fourth stage cylinder group, proceed as follows: When cylinder liner (14) is pressed into cylinder (15), make certain that oil hole in skirt of liner (14) is aligned with oil hole in cylinder (15).  Assemble cylinder to crankcase with the oil inlet hole on top side. (1) If cylinder liner (14) was disassembled from cylinder (15), press into position aligning oil hole in liner skirt with oil hole in cylinder.  Assemble pipe plug (12) if removed at disassembly NOTE A repair kit consisting of lentoid springs (7), valve ring (8), closing spring (9), and valve disc (10) is available.  At overhaul these parts shall be replaced as a set. Assemble lentoid springs (7) as illustrated on Figure 6-8. (2) At overhaul of intake-exhaust valve assembly (5) use available repair kit.  Assemble valve disc (10), closing spring (9), and assemble the upper guard onto seat.  Install valve ring (8) and four lentoid springs (7) (see Figure 6-8) and assemble lower guard into seat. (3) Assemble  valve  gasket  (11), intake- exhaust valve assembly (5), head gasket (4), cylinder head (1) and secure with lock washers (3) and cap screws (2).  Torque cap screws (2) to 45 pounds foot (Table 6- 1). 6-21. Fourth Stage Piston and Pin Assembly (See Figure 8-18).   The  following paragraphs  contain disassembly, cleaning, inspection, repair or replacement, and assembly instructions for the fourth stage piston assembly. a. Disassembly.  Disassemble the fourth stage piston assembly only to tile extent necessary to repair or replace a defective part or parts. 6-28