Mercury Optimax Models 135, 150, Direct Fuel Injection., Page 252Get this manual
POWERHEAD
MEASURING PISTON ROUNDNESS
Piston has barrel profile shape and is not true diameterStandard 135150 Models153 cuin(2508 cc) 1Using micrometer, measure dimension "A" at location shownDimension "A" should be as indicated in chart followingPiston Standard Piston 0.015 inOversize Piston Dimension "A" 3.4925 in 0.0005 in3.5075 in 0.0005 in
2Using micrometer, measure dimension "B" at location shownDimension "B" should be within 0.008 inof dimension "A
0.700 in(17.78mm)
aDimension "A" at RIGHT Angle (90) to Piston PinDimension "B" (in line with Piston Pin)