Perfect for purchased 32mm piston rings. But the tube arrived with 1.275 I.D., well within the industry tolerances, smooth, round, and ready for honing. But that is 32.39mm, so I guess I need to go to 33mm rings (which I now have) and somehow fit them to the 32.39 bore. I feel that trying to bore the tube out to 33mm would leave me disappointed. A. Wiseco Powersports pistons are designed for optimal piston to wall clearance for the specific bore size of your engine. For example, your 125cc dirt bike engine is 54mm bore, the Wiseco piston is designed just for that bore size, and does not require any specific adjustments to fit properly. Sep 02, 2016 · Adding the main bearing bore radius to 7.7045" results in a deck height of 9.0246"-9.025". If you have an engine other than a small block Chevy, you need to find the main bearing bore of the motor or snug a cap onto the saddle without a bearing and measure the diameter, then divide that figure in half for the radius.