Inspecting, Testing, and Repairing Cylinder Heads

Inspecting, Testing and Repairing Valves and Valve Assemblies

Engineman 2 - Intermediate engine mechanics training manual
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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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