The valve which allows mixture into the cylinder is the inlet valve; the one through which the spent gases escape is the exhaust valve. They are designed to open and close at precise moments, to allow the engine to run efficiently at all speeds.
The operation is controlled by pear-shaped lobes, called cams, on a rotating shaft, the camshaft, driven by a chain, a belt, or a set of gears from the crankshaft.
To avoid valve related problems down the road, do the following:
- Analyze the amount of wear as well as wearpatterns in the head and valvetrain components when the head is disassembled. A careful inspection should reveal any abnormal conditions or wear patterns that would indicate additional problems.
- Inspect each and every component in the valvetrain and head so all worn or damaged parts can be identified and replaced or reconditioned.
- Keep a close watch over production quality so the parts that are being reconditioned are done so correctly.
- Pay attention to specs, critical dimensions and rocker arm geometry to assure proper reassembly.