Compression System

State of the Piston Head, Valves and Head Gasket

Determining Top Dead Center

By rotating the clutch, you will be able to see the rocker arms moving up and down.

The rockers are moving because the ends of the push rods are sitting ontop of the cam! This will rock the rockers back and forth. When the push rod goes up, it compresses the spring which allows the valve to open. When the cam allows the push rod to come back down the spring pushes back on the rocker and the valve closes.

Watch the video above to learn how these connected move to get the piston to "Top Dead Centre"

Piston to Wall Clearance

The clearance between the pison and wall varies greatly depending on material used to make the block and the piston itself to the method of cooling the engine. The greater the thermal expansion of the material, the more clearance is needed.

If an engine has large fins like those seen on the side, they are air cooled, which means the thermal expansion of the metals that make up the block and pistons are dependent on the temperature of the air around them!

Larger engines will use tunnels to pump a fluid (coolant) that keeps the entire engine at a lower more even temperature, decreasing the effects of thermal expansion and allowing for less gap betweent the piston and wall.

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