piston to wall measurement
Is this correct?
Or is it .0020 - .0025 bore size larger than piston size?
Correct, they are calling for the Bore Diameter, to be .0020" to .0025" larger than the Piston.
That is a "minimum" reccomended clearance for installation.
Additional clearance may be required as per the application... C.R., RPM intended, Etc., etc.
USE A TORQUE PLATE, or you will have problems at THAT .0020"to .0025"minimum sizing.
IMO,
If no Torque Plate is used, add about .0005" for a safety factor, me personally... I would just default to .0030" on a BB 440 Engine anyways even with the T/Plate.
Is this a BB or SB Engine ? Whats the Bore size ?