LO 9-9 Identify and describe the purpose, construction, and applications of cylinder head gaskets
1. Cylinder Head Gaskets
1.1. Head Gasket Replacement
LO 9-09: Identify and describe the purpose, construction, and applications of cylinder head gaskets. |
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Head Gasket Replacement To prevent warping of cylinder heads, damaged bolts and threads, and gasket leakage, consistent and adequate clamping of cylinder heads is necessary. A traditional technique for clamping cylinder heads to the block requires the use of a torque wrench and a spiral pattern sequence for tightening the head bolts down in the correct order. Starting at the center of the cylinder head and working out, this technique prevents pinching of the head gasket by ensuring an even spreading out of the gasket from the gasket center out and along the block deck surface. Any bolt-tightening sequence should tighten the cylinder head down in a minimum of three progressive steps of torque, and five or six steps is not uncommon Figure 68. Reversing this tightening pattern when removing a cylinder head will prevent warping of the head. It is especially important to follow this practice in the case of aluminum cylinder heads. After removing a cylinder head, it should be checked for warping. Generally, no more than 0.006" (0.015 mm) of warping per foot (30 cm) is allowed on a cylinder head. Manufacturers’ specifications and techniques will vary. Diesel engines are allowed very little removal of material from the cylinder head or block deck during resurfacing because machining will cause valve-to-piston interference Figure 69. |
FIGURE 09-68: A spiral pattern of three to five progressive steps of torque, starting from the center and working toward the ends, is used to tighten head bolts. |
FIGURE 09-69: Because there are very small clearances between the valves and the pistons in a diesel engine, very little material can be milled from a cylinder head to correct warpage. |
FIGURE 09-70: Improper liner protrusion can lead to a cracked or warped head plus a head gasket leak. |
While diesel engine cylinder heads are ruggedly built, they can be warped and cracked by incorrect liner protrusions. A liner flange that protrudes too far above the block deck can allow combustion gases and coolant to leak because the head gasket does not seal properly, and it can also distort the cylinder head. Remember that the clamping forces of 36–42 head bolts can add up to over 1,000,000 lb (453,592 kg) of force applied by the head to the block deck through the gasket. A protruding liner allows those forces to be exerted on a small area Figure 70.
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