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Well, I'll take a shot at this because nobody else is.

First, is this a standard-bore block? The wear pattern you described is not normal. If it is a stock rebuild with no cylinder work, I would measure the diameter across the bore from a variety of angles (i.e., parallel to the crank, perpendicular to the crank, 45* to those, etc.) to establish that the bore is actually round.

If the block has been bored recently, it's almost inconceivable that the cylinder could be out of round...but not impossible. If it was bored/honed, was a torque plate used? The 5.0 liter block is actually relatively flexible, and mounting the heads introduces some flex. To counteract this, many machine shops use a 'torque plate' during machining, which is a big chunk of steel or aluminum that bolts to the block using head bolts, but has oversize holes through it to allow machine access to the cylinders. Theoretically, the cylinders could go out-of-round when the torque plate is removed, then go back into round when the heads are installed.

Completely different thought: what kind of rings are being used? Is it possible that you got one bad ring in the box? How do the others look, or did you only pull the one set?

Hope this helps.

AJ
 
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