Yamaha Marine Outboards F4A/F4 Factory Service Manual, Page 184Get this manual
CRANKCASE, CRANKSHAFT AND CAMSHAFT
SERVICE POINTS
1 Crankcase removal 1Remove: 9Crankcase 9Cylinder body 2
9Position the crankcase up side down9Insert flat-head screwdriver between the tabs on both side of the crankcase and cylinder body and pry open the two parts
Do not scratch the interface of the crankcase and cylinderCylinder inspection 1Measure: 9Cylinder bore Out of specification Rebore or replace the cylinderNOTE: Measure the cylinder bore in parallel and at right angle to the crankshaftThen, average the measurementsD2