Checking piston-to-wall clearance is a critical measurement every engine build should include. Here is a detailed walk through of how to measure your piston-to-wall-clearance.
A feeler gauge is no longer an option when determining piston-to-wall clearance on a high-performance or racing engine. Even though photos depicting engine builders checking this dimension using the thin blades are found in instructional books and on the Internet, the accuracy of the numbers is not reliable—and today’s leading engine builders are demanding exact tolerances to ensure reliability and performance.
Therefore, precise measurements of the piston and cylinder bore diameters are crucial toward calculating piston-to-wall clearance—which is critical for two reasons. If there’s too much clearance, the piston could rock back and forth inside the cylinder and damage the rings, cylinder walls, or skirts. If the clearance is too tight, then the piston can seize in the cylinder as it expands due to combustion heat.
Diamond carefully specs the piston-to-wall clearance with each and every piston they sell, but checking it in relation to the bore is a mandatory part of the assembly process. You see, things like bore wear, and honing tolerance all need to be verified to ensure an engine build is successful. Diamond sets the gauge point for its pistons by measuring down from the bottom of the oil-ring groove and in the below photo sequence, we'll show you everything you need to know to check the piston-to-wall clearance on your next build.