TM   5-4930-227-14 CHAPTER 6 REPAIR  INSTRUCTIONS Section I. ENGINE COMPONENTS 6-1.  General a. Cylinder Head. The cylinder head covers the top of the cylinder and provides a mounting port for the spark plug. It is finned to help dissipate the heat of engine combustion. b.  Valve  Tappets.  Intake  and  exhaust  valves have tappets which raise the valves at the re- quired  portion  of  the  engine  operation  cycle. These tappets operate in conjunction with the camshaft. Valve tappet clearance can be checked without  major  engine  disassembly,  but  it  cannot be  adjusted  without  disassembly. 6-2. Cylinder Head a.  Removal. (1) Remove the spark plug (para 3-23). (2)  Remove  the  air  shroud  (para  3-20). (3)  Refer  to  figure  6-1  and  remove  the cylinder  head  and  gasket. b.   Cleaning   and   Inspection. (1)  Discard  the  cylinder  head  gasket.  Clean the cylinder head and cylinder head bolts with an  approved  cleaning  solvent;  scrape  carbon  de- posits  from  the  cylinder  head,  taking  care  not  to scratch sealing surfaces. (2)  When  the  cylinder  head  is  removed, clean the top of the cylinder block, carefully re- moving carbon from piston tops and from around the  valve  head  and  seats.  Take  care  not  to  scratch or  score  valve  seats. (3)  Inspect  the  cylinder  head  for  cracks, warping,  broken  cooling  fins,  spark  plug  port threads, and other damage. Straighten bent cool- ing  fins.  Replace  a  damaged  cylinder  head. c.  Installation. (1) Refer to figure 6-1 and install the cylin- der  head,  using  a  new  gasket. (2) Install the air shroud (para 3-20). (3)  Install  the  spark  plug  (para  3-23). (4) After installation of air shroud, torque all cylinder head mounting bolts, following the sequence shown in figure 6-2. 6-3. Tappet Cover Plate and Tappets a.  Removal.  Refer  to  figure  6-3  and  remove the  tappet  cover  plate. b.  Cleaning  and  Inspection. (1)  Clean  the  cover  plate  and  accessible metal parts with an approved cleaning solvent and  dry  thoroughly. (2)  Measure  valve  clearance  (fig.  6-3)  and inspect  for  defective  valve  springs,  tappets,  rota- tors,  and  seats. c. Installation. Refer to figure 6-3 and install the  tappet  cover  plate. 6-4. Valves, Valve Seats, Guides, and Springs a.  Removal. (1)  Remove  the  engine  (para  3-17). (2)  Remove  the  carburetor  (para  3-28). (3)  Remove  the  muffler  (para  3-31). (4) Remove the cylinder head (para 6-2). (5) Remove the tappet cover plate (para 6- 3). b. Disassembly. Refer to figure 6-4 and disas- semble  the  valves,  valve  seats,  guides  and  springs. c. Cleaning, Inspection, and Repair. (1)  Clean  the  valves  with  a  wire  brush  to remove  all  carbon  deposits.  Clean  valve  seats, ports, and guides in cylinder block; clean top of cylinder block. Wash springs with an approved cleaning solvent and dry thoroughly. (2)  Inspect  valves  for  burned,  pitted,  or cracked faces; replace a burned, cracked, or deep- ly pitted valve. (3) Inspect valve springs for cracks or pit- ting.  Replace  cracked  or  pitted  springs. (4)  Inspect  valve  seat  insert  for  looseness and  pitting.  Replace  a  defective  valve  seat  insert in  the  following  manner: (a) Use a puller to remove the insert from the  exhaust  valve  opening. (b)  Clean  all  carbon  out  of  the  insert counterbore in the cylinder block and clean the valve  stem  guide  bore. 6-1