Alan
Here's what I do to assemble a matched piston cylinder set:
1. Make sure the cylinder ht groups are the same on each engine bank. Either all (6) the same ht group or (3) of one ht group and (3) of the second ht group.
2. Weigh each piston and make sure the difference between the lightest and heaviest is less than 8 grams
3. Check the ring land end clearances to make sure they are in spec. The top compression ring land takes the most wear and is most critical
4. Measure the piston diameters perpendicular to the wrist pin axis, about 1/4" below the wrist pin. This requires a precision micrometer
5. Measure the cylinder bore diameters at top and bottom stoke locations, at 90 degrees apart (4 measurements). make sure the cylinders are not worn beyond spec diameter and that the ovality or difference between the largest and smallest diameter does not exceed 0.4mm. This requires a bore gauge calibrated to the same micrometer used for the piston measurements.
6. I then plot the diameter data and match large and small pistons and cylinders to obtain piston to cylinder clearance less than 0.10 mm
Here is an example copy of the plot and data sheet I use.
Hope this helps
