Engine Building Fundamentals: Feeler Blades
- Feeler blades, or feeler gauges, are a set of small lengths of steel, of precise thickness.
The thickness of each feeler blade is marked on the material, and they are used to measure the thickness or width of a gap.
A common use of feeler blades would be to check the end gap of a piston ring, by checking which width feeler blade will just fit between the end gap of the piston ring.
Feeler blades are also commonly used to check valve clearances by placing the feeler blade between the valve tip and the rocker arm, or alternatively between the cam and a roller rocker.
Using a feeler blade does require developing a feel for when you have the correct blade for the gap you're measuring.
There should be a slight friction between the blade and the part you're measuring, but the blade should still be easy to slide through the gap with a gentle push.
If the feeler blade you're using is too small, then there'll be no resistance at all, whereas if the feeler blade is too large, then you'll find it requires a lot of effort to force the blade through the gap.