2005 Yamaha F90TR 90HP Outboards Factory Service Manual, Page 107Get this manual
Power unit Piston clearance: 0.0700.080 mm (0.00280.0031 in)
Checking the cylinder bore
1Measure the cylinder bore (D1D6) at measuring points a, b, and c, and in direction (D1, D3, D5), which is parallel to the crankshaft, and direction (D2, D4, D6), which is at right angle to the crankshaft
Checking the piston rings
1Check the piston ring dimensions of and TReplace if out of specification