Yamaha Marine Outboards Factory Service / Repair/ Workshop Manual 225G 250B L250B, Page 210Get this manual
SHIMMING (COUNTER ROTATION MODELS)
SHIMMING (COUNTER ROTATION MODELS)
NOTE: There is no need to select shims when reassembling with the original case and inner parts Shim calculations are required when reassembling with the original inner parts and new case (the difference between the original inner parts and the new case) Measurements and adjustments are required when replacing the inner part(s)