Which tool is used to measure the flatness of a cylinder head machine surface?

The tool used to measure the flatness of a cylinder head machine surface is a surface plate and feeler gauge. A surface plate is a flat, solid plate used as a reference point to assess the flatness of the cylinder head. It provides a stable surface against which the cylinder head can be placed.

Feeler gauges, which are typically made from thin strips of metal with varying thicknesses, are then used to check the gaps between the cylinder head and the surface plate. By inserting these feeler gauges into any gaps, a technician can determine if the cylinder head is flat or if there are high or low spots that need to be addressed. This method allows for a precise assessment of flatness, which is crucial for ensuring proper sealing and engine performance.

Other tools mentioned, such as an inside micrometer, are designed for measuring internal dimensions of holes or cylinders, while a dial indicator is more commonly used to measure small distances or variations in movement. A caliper is generally used for measuring external and internal dimensions and depth, not specifically for assessing flatness. Hence, the combination of a surface plate and feeler gauge is the best choice for this particular measurement task.