We used a dial indicator on a cylinder-bridge tool to position TDC. You could also use a dial indicator with a magnetic base for this. Place the dial indicator over the cylinder and set the zero mark at roughly the piston's highest point. Rotate the engine counterclockwise to 0.100 inch down and then rotate the crank clockwise to where the piston is 0.050 inch down in the bore. Record the degree-wheel reading. Then continue to rotate the piston clockwise through TDC to 0.050 inch down on the dial indicator to the opposite side of TDC and read the degree wheel. The two numbers will be the same when TDC is positioned accurately.