2000 Yamaha YFM400FWA(M) Factory Service workshop Manual, Page 151Get this manual
CYLINDER AND PISTON
3rd step: Find the piston-to-cylinder clearance with the following formulaPiston-to-cylinder clearanceCylinder bore "C" Piston skirt diameter "P" Piston-to-cylinder clearance: 0.0400.065 mm (0.00160.0026 in) Limit: 0.15 mm (0.0059 in)