I tore down my engine to a shortblock today. Reason for this is a h/c/i and carburetion swap. While I was in there i decided to pull off the harmonic balancer....as soon as i put my hands on it i realized i was able to slide the crankshaft front to back like a 1/4 of an inch!!!! This is bad, seeing as how endplay is allowed 0.012 max. The engine only has 2000 miles on it. I did not build this, bought it in the car. Judging by the condition of the internals i can safely say that mileage is correct (still crisp cross-hatch, no sludge, pistons still somewhat clean). It is a 306 with a 0.010" undercut stock crank, fresh factory rods and KB forged pistons, the whole rotating assembly was balanced as well (grinding marks fresh on the connecting rod caps).... My first thought of course is to check out the thrust bearing....perfect condition, not even a scratch on it or the crankshaft. When the engine was in the car, it ran beautiful. 50psi of oil pressure, and pulled to 6000 rpm smooth as can be. Could it be the wrong thickness on the thrust bearing? Are there different sizes to fill in this gap? Am i completely screwed? Please help with any input you might have. Thanks