2010-2012 PRO-RIDE RUSH Switchback RMK Service Manual, Page 91Get this manual
EngineCoolingExhaust Piston Inspection
Check piston for scoring or cracks in piston crown or pin areaExcessive carbon buildup below the ring lands is an indication of piston, ring or cylinder wearUsing only micrometer, measure the piston outside diameter at 90 angle to the direction of the piston pin and at the specified measuring pointNOTE: micrometer is the only recommended tool to accurately measure piston diameter
Piston Ring Installed Gap
Position the ring 20mm from the top of the cylinder using the piston to push it squarely into placeMeasure installed gap with feeler gauge at both the top and bottom of the cylinderNOTE: difference in end gap indicates cylinder taperThe cylinder should be measured for excessive taper and out-of-roundReplace rings if the installed end gap exceeds the service limitAlways check piston ring installed gap after re-boring cylinder or when installing new rings