LO 9-5 Identify and describe the purpose, construction, and operation of components used in the valve train

LO 9-05: Identify and describe the purpose, construction, and operation of components used in the valve train.

Valve Cooling

Because exhaust gas temperatures can momentarily exceed 1200° F (649° C) as they exit the valve port, valve damage can occur if heat is not removed from the valve. Excess heat must be removed to prevent burning, breakage of the valve stem and head where they are welded, and seat warpage. If the seat is warped, burned, or damaged, the result can lead to valve leakage. Good seat contact provided by a three-angle valve cut of the valve head is important for good heat transfer from the valve to the seat. Also, mechanically rotating the valve slightly with an automatic mechanism each time it opens can eliminate localized hot spots that can lead to valve burning. Valve rotators are commonly installed on either the bottom or the top of at least the exhaust valve to produce this rotation Figure 40. Intake valves are cooled by intake air entering the cylinder and flowing over the valve face and seat. During the valve overlap period, cooler air passes over the exhaust valve face and seat, passing out of the cylinder with exhaust gases.

FIGURE 09-40: The top of a dual valve spring. The inner spring rubs against the outer spring to minimize valve float, and the rotator turns the valve each time it opens and closes to help cool the valve.

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