Yamaha F100B F100C Outboards Factory Service Manual, Page 134Get this manual
Power unit
Checking the piston clearance
1Rebore the cylinder or replace the piston and piston rings as set, or the cylinder body, or all parts if out of specificationPiston clearance: 0.070.08 mm (0.00280.0031 in)
Checking the piston rings
1Check the piston ring dimensions of and TReplace if out of specification