Fitting Pistons & Rings
- Measure piston diameter at bottom of skirt about 9/16" 15 mm) from edge. Take measurement at 90° to pin bore. Measure internal diameter of cylinder sleeve with cylinder bore gauge or internal micrometer. Take measurement 3/8-5/8" (l0-16 mm) from top of sleeve.
- Piston skirt clearance is difference between sleeve diameter and piston diameter. Wear limit is .008" (.20 mm) while new clearance is .001-.002" (.03-.06 mm). Measure piston recess depth from top edge of crown to bottom of recess in crown. See Fig 1. This measurement should be .458" (11.65 mm).
- Push ring squarely into lower end of sleeve about 3/16 (4-5 mm) and measure ring end gap. Upper and lower compression ring gap wear limit is .035" (.90 mm). Oil scraper ring gap wear limit is 037" (.95 mm). Install rings with "TOP" mark facing crown of piston. See Fig 2.
NOTE: Measure side clearance between face of ring and piston groove.
- Measure side clearance between face of ring and side of ring land. Upper compression ring side clearance has wear limit of 005" (.12 mm). Lower compression and oil scraper ring side clearance wear limit is .004" (.10 mm).
- Size, weight and installation direction are marked on crown of piston. Arrow must point to flywheel when piston is installed. Weight group is indicated by "+" or "-" mark. Pistons marked "+" weigh 16.12-16.37 ozs. (457-464 g). Pistons marked "-" weigh 15.80-16.08 ozs. (448-456 g).
- Maximum weight difference between pistons is .35 ozs. (10 g). Paint dot (Blue for standard) is for matching sleeve diameter size to piston diameter. Piston diameter is measured in millimeters and given as 4 digit number stamped into face.