1999 Volvo Penta "WT" Models Workshop Manual, Page 198Get this manual
Piston Selection Measuring the Piston Check the used piston to cylinder bore clearance, as follows:
1Cylinder bore diameterUse telescoping bore gauge, located 2.5 in(65 mm) below the top of the cylinder bore
2Piston diameterMeasure the skirt at right angle to the piston pin hole, 1.0 in(25 mm) below the oil ring grooveMeasure piston diameter at 70 degrees (20 degrees C)DRC6507
3Subtract the piston diameter from the cylinder bore diameter to determine piston to bore clearance4Locate the piston-to-bore clearance, refer to Engine SpecificationsDetermine if the piston-to-bore clearance is within the acceptable range