2000-2005 Yamaha F40B Outboard Service Manual, Page 266Get this manual
CRANKSHAFT AND PISTON
INSTALLING THE PISTON RING
Do not scratch the piston nor break the piston ringsAfter installing the piston rings, check that they move smoothly
Install: Oil ring 2nd ring Top ring NOTE: _ Offset the piston-ring end gaps as shownPiston rings should be replaced as set
INSTALLING IN THE ENGINE
Check that the upper oil ring gap is positioned with its locating pin and then install the piston assemblyInstall the piston with the "UP" mark on the piston crown facing towards the flywheel side