OK, more info:
180 degree thermostat, checkd in a water bath with an accurate thermometer, amnd it's working OK. New water pump. The original engine was prone to overheat, but that's fixed. Cam is new, original equipment specs, and degrees out OK. I'm suspecting a hot spot in the cylinder head, causing the #1 cylinder to run hot/lean. The scoring is on the thrust face of the piston, and corresponding cylinder damage. On both previous teardowns, the wrist pin is tight, but nor siezed in the piston. Rods have been resized, and checked for straightness and twist. Everything Ok so far! We're about to pull the head, and have it checked for restrictions and/or cracks in the #1 cylinder area. The head is the only thing that's common to all jobs so far. Pistons, crank, rods, etc. have been checked and/or replaced or reconditioned on every assembly, with no problems noted. Mixture checks out OK on a 4-gas exhaust analyzer, so overall mixture is OK.
Jerry
