Inspecting, Testing, and Repairing Cylinder Heads

Figure 3-9.—Removing a cylinder liner. 4. Attach the special liner puller to the liner studs and tighten the nuts by hand. (The nuts must be hand tightened; if a wrench is used, the threads on both the nuts and the studs may be damaged.) 5.   Attach the hook of the chain fall and pull slightly until the liner breaks free (fig. 3-9). If the liner fails to break loose immediately, apply pressure at the bottom of the liner. To do this, place a block of wood on the crankshaft  throw,  and  force  it  up  against  the  liner  by rotating  the  turning  gear. 6.  Lift  the  liner  up  until  it  clears  the  top  of  the engine block and remove it to a safe place. You may need to rotate the liner slightly while removing it from the engine  block. INSPECTING, TESTING, AND REPAIRING  CYLINDER  HEADS Conditions requiring repair of a cylinder head are similar to those for cylinder liners and can be grouped under cracks, corrosion, distortion, and fouling. CRACKS The symptoms of a cracked cylinder head are the same  as  those  of  a  cracked  liner.  Cracks  in  cylinder heads  are  best  located  by  either  visual  inspection  or magnetic powder inspection. On some types of engines, a  defective  cylinder  can  be  located  by  bringing  the piston of each cylinder, in turn, to top dead center and applying  compressed  air.  When  air  is  applied  to  a damaged cylinder, a bubbling sound indicates leakage. When the cylinder head is removed from the engine, it can be checked for cracks by the hydrostatic test used on  cylinder  liners  equipped  with  integral  cooling passages. Cracks  generally  occur  in  cylinder  heads  on  the narrow  metal  sections  between  such  parts  as  valves  and injectors.  The  cracks  may  be  caused  by  adding  cold water to a hot engine, by restricted cooling passages, by obstructions in the combustion space, or by improper tightening  of  studs. Aboard ship, cracked cylinder heads usually must be replaced. It is possible to repair them by welding, but this  process  requires  special  equipment  and  highly skilled   personnel   normally   found   only   at   repair activities. CORROSION Burning and corrosion of the mating surfaces of a cylinder  head  may  be  caused  by  a  defective  gasket. Although   regular   planned   maintenance   ordinarily prevents this type of trouble, burning and corrosion may still take place under certain conditions. When corrosion and burning occur, there may be a loss of power due to combustion gas leakage out of or water leakage into the combustion space. Other symptoms of leakage may be (1) hissing or sizzling in the head where gases or water may be leaking between the cylinder head and the block, (2) bubbles in the cooling water expansion tank sight glass, or (3) overflow of the expansion tank. Gaskets and grommets that seal combustion spaces and water passages must be in good condition; otherwise the fluids will leak and cause corrosion or burning of the area contacted. Improper cooling water treatment may also accelerate the rate of corrosion. In  general,  cylinder  heads  that  are  burned  or corroded by gas or water leakage are so damaged that they must be replaced. 3-7


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