How are cylinder heads checked for warping?

Cylinder heads are typically checked for warping using a straightedge and feeler gauges. A straightedge is placed across the surface of the cylinder head, and any gaps between the straightedge and the head can be measured with feeler gauges. If the gap exceeds the manufacturer's specified tolerance, the head is considered warped and may require machining or replacement. Additionally, some shops may use a dial indicator for a more precise measurement of surface flatness.