This is where the truth comes home on everything. Here, Marvin degrees the camshaft and checks true top-dead-center. Manufacturing tolerances can vary in crankshafts, connecting rods, pistons, bearings, and camshafts. This is why, at the least, Marvin degrees the cam to check out true timing events. He also checks the #1 piston for true top-dead-center. And if you're really on the ball, you check all eight cylinders.