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Nowadays, coating technology inside the engine is becoming more and more common, it is a reliable method to improve the performance and wear characteristics and overall life of racing engine components. JE Pistons provides some useful suggestions for measuring the overall piston diameter of coated pistons. These measurements help to calculate the formula between the piston skirt and the cylinder bore, better described as the piston-to-wall clearance.

When building a new engine, it is essential to measure the piston-to-wall clearance. In extremely critical racing engine manufacturing applications, the thermal expansion of the piston requires precise tolerances. The most commonly used in racing cars is forged pistons, which expand more than cast pistons, so attention to detail is required.

Essentially, there are the right tools and measuring procedures, unfortunately, the common wrong way to measure the diameter of coated pistons. For example, JE’s engineers strongly recommend not to use calipers when measuring the diameter of a piston.

Using simpler equipment (such as calipers) may cause false readings of up to 0.003 inches. Different piston manufacturers may vary the gap between the piston and the wall, depending on the piston material they use. Regardless of your specific tolerances, their measurement accuracy is usually as low as 0.0001 inches.

Accurate cylinder bore and piston diameter measurement

Measuring the bore of your engine block requires a precision dial indicator. Almost, this is the end of the discussion. A high-end dial indicator is the tool of choice. Similar to using incorrect calipers when measuring pistons, calipers are another tool that cannot provide the required accuracy.

Using the popular JE Perfect Skirt coated piston to measure the diameter of the piston requires a blade micrometer to measure it. Displayed next to the traditional cylindrical end unit, the blade micrometer will accurately measure the skirt of the piston within the provided piston coating window. Measurements made while touching the coated surface will cause inaccurate readings.

All pistons are not perfectly round; in fact, they are described as the diameter of a "cam" shape. By following the specific "measuring point" locations carefully pointed out by JE Pistons in their graphic descriptions, you will get the correct measurements to match your cylinder bore and obtain the proper piston-to-wall clearance.

The caliper does not have the accuracy to reliably measure the precision skirt of the piston, and should not be used for any piston measurement. The JE specification sheet included with all piston sets shows all correct measurement points for coated pistons.

With careful attention to details and proper use of tools, your Perfect Skirt coated piston will help eliminate piston slapping and prevent premature wear on the skirt. Just a few simple details in the engine assembly, you can incorporate the coated piston into your engine manufacturing plan.

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