Video: MAHLE Motorsports Explains How to Measure For Piston to Cylinder Wall Clearance

Back in December, we learned how to understand why bearings fail, thanks to MAHLE’s Bill McKnight. This is was only one of many videos the company (and Bill) has released to help gear heads understand components inside the engine.

In this video, the tech gets thrown over to Trey McFarland, the Sales Manager of MAHLE Motorsports. He breaks down how to measure piston to cylinder bore clearance, and also goes over some important concepts and design features of the MAHLE pistons.

 

Trey explains that using the proper measuring point on the piston is important. This is because every MAHLE Motorsports piston has a unique profile, and if you measure above or below the proper measuring point, you’re going to get a false reading. Basically, the curvature of the design will cause the measurement to be incorrect if it’s not measured at the right point.

Once you know the measuring point, it’s time to mark it. For example, the piston in the video has a measuring point of 0.250” up from the skirt. Measure to the point for your piston, and mark it on each side. Then take your micrometer and align it with the marks on both sides — this will give you your piston measurement.

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After the piston dimension is checked and the measurement is now determined, the cylinders will need to be checked. You’ll do this using a dial bore gauge. The cylinder bore measured 4.0402” (that’s 2/10ths added to the gauged dialed in at 4.040”). The pistons measured out at 4.0370.” so that gives a working piston-to-wall clearance of 0.0032,” which is in the range acceptable for the piston being used.

There are some variables that can affect your measurements: temperature and coating. The parts need to be measured at
room temperature. As far as the coating goes, this is factored into the acceptable range already.

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Thanks to MAHLE Motorsports and Trey McFarland for this super simple way to find out the piston to cylinder wall clearance!

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