2006 Johnson SD 30 HP 4 Stroke Outboards Service Manual, PN 5006592, Page 154Get this manual
POWERHEAD PISTON, CYLINDER, AND CRANKSHAFT Check the water jackets for clogs or obstructionsThe difference between the two depth measurements is the cylinder bore taperThe difference between the axial and transverse measurements is the cylinder bore out-of-roundThe service limit for cylinder bore wear is 0.004 in(0 .10 mm)If either the taper or out-of-round measurement exceeds this specification, rebore or replace the cylinderUse micrometer to measure the piston diameter at point 0.75 in(19 mm) above the piston skirt at 90 angle to the wrist pin boreCylinder Bore and Piston Skirt Specifications 2.5591 to 2.5598 inCylinder Bore Diameter (65.000 to 65.020 mm) 2.5579 to 2.5587 inPiston Skirt Diameter (64.970 to 64.990 mm)
Water jacket
Inspect the cylinder walls for scratches, roughness, or ridges which indicate excessive wearIf damaged or worn, rebore the cylinder and use an oversize pistonUse cylinder gauge to measure the cylinder bore in the axial direction (vertical line following crankshaft) and the transverse direction (horizontal line across crankshaft)Take measurements at two different depths: 2.0 in(50 mm) and 3.5 in(90 mm)001546