My experience only goes back sixty years or so, but the clearance was always in the piston. The cylinder is bored to the specified diameter and the piston should be correspondingly smaller to provide the specified clearance.
Back in the bad old days, Studebaker and Packard machining lines couldn't hold a tolerance and neither could piston manufacturers. After the blocks were bored and honed, they were measured and a letter code corresponding to a dimension was stamped on the bottom edge of the cylinder. Pistons were measured and put into boxes with corresponding letter codes. The short block assembler looked at the letter codes and chose the matching pistons. Today, pistons are CNC finished and are dead nuts on diameter and weight. Even though they're usually dead on, we will never bore a block without having the pistons on the bench to confirm their diameter.
None of us wants to admit how sloppy production tolerances were back when, but we're working with a NOS Champion block and the cylinders vary .003". Today, when we're honing the block, each cylinder is finished the same diameter within .0002".
Again, how crude we were back when, Studebaker Shop Manuals assumed small dealerships and repair shops would not have micrometers, so they don't specifiy piston-to-wall dimensions. Sometimes, look at the Shop Manual photos, showing using a long feeler gauge and a fish scale to measure drag as an estimate of the clearance.
As to cylinder wall finishes, how smooth and/or how rough cannot be discussed without specifying which rings are to be used. Cast iron, chrome and moly rings each have a different cylinder surface finish specification. Again, today is better; we use diamond abrasives and power stroke machines to produce round cylinders with the proper texture. When the cylinders are properly finished, rings seat immediately.
jack vines
Back in the bad old days, Studebaker and Packard machining lines couldn't hold a tolerance and neither could piston manufacturers. After the blocks were bored and honed, they were measured and a letter code corresponding to a dimension was stamped on the bottom edge of the cylinder. Pistons were measured and put into boxes with corresponding letter codes. The short block assembler looked at the letter codes and chose the matching pistons. Today, pistons are CNC finished and are dead nuts on diameter and weight. Even though they're usually dead on, we will never bore a block without having the pistons on the bench to confirm their diameter.
None of us wants to admit how sloppy production tolerances were back when, but we're working with a NOS Champion block and the cylinders vary .003". Today, when we're honing the block, each cylinder is finished the same diameter within .0002".
Again, how crude we were back when, Studebaker Shop Manuals assumed small dealerships and repair shops would not have micrometers, so they don't specifiy piston-to-wall dimensions. Sometimes, look at the Shop Manual photos, showing using a long feeler gauge and a fish scale to measure drag as an estimate of the clearance.
As to cylinder wall finishes, how smooth and/or how rough cannot be discussed without specifying which rings are to be used. Cast iron, chrome and moly rings each have a different cylinder surface finish specification. Again, today is better; we use diamond abrasives and power stroke machines to produce round cylinders with the proper texture. When the cylinders are properly finished, rings seat immediately.
jack vines
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