How to check flatness using an engineer’s straight edge?

29th February 2020


How to check flatness using an engineer’s straight edge


	Shop for Engineer’s Straight Edges


		Other equipment you will need:
		Feeler gauge Feeler gauges are thin strips of metal used to measure very small gaps between two objects.

		Light Fluorescent glare free light is used to check for gaps between the straight edge working face and workpiece.

		Spirit level Placed on top of an I section or rectangular straight edge, a spirit level can help check if the workpiece surface is level as well as flat.

		Checking an engine block or cylinder head is flat
		An engineer’s straight edge can be used to check that an engine block or cylinder head is flat by being placed across its surface.

		By shining a light behind the straight edge, any gaps between the cylinder head surface and straight edge will be visible if they are more than 0.002mm in size. The light is easier to see, the thinner the straight edge is, so knife edge straight edges are the most accurate for this task, although you do have to hold them, as they will not stand up on their own.

		Any gaps should then be measured using a feeler gauge.

		This process has to be repeated across six areas of the cylinder head. If gaps in any area are outside of the permitted tolerance for that engine, then the cylinder head will need resurfacing. This process then has to be repeated on the cylinder block in order to achieve a fit within the tolerances for the cylinder head and block combined.