unchecked along the valve stem, engine HC emissions will become excessive. To control this, an elastomeric seal is fitted over the top of the valve guide. These may wear or stiffen with age, so are usually replaced whenever valves are removed for servicing.

Wear

Over time, the inner diameter of the valve guide and the outer diameter of the valve stem may become worn. Moreover, the valve guide is exposed to high temperatures during operation, which can reduce

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