Cylinder Bore Clearance
Measure cylinder bore clearance before installing the pistons back into the engine block. Today's vehicles have extremely tight maximum allowable clearances. The cylinder’s taper and out of round dictate whether a cylinder is acceptable or if the engine block needs to be bored.
Out of Round: An out of round cylinder is out of round when beyond specifications. When a cylinder wall is new it is perfectly round. They must be in excellent condition before piston installation.
Pressures exerted at the top of the ring travel and at the thrust and non-thrust surfaces take their toll over time. Pressure is most at the top and at a point 90° to the piston pin. Measure for out of round and taper before reconditioning the cylinder walls.
Taper: Taper is the difference in the diameter of the cylinder between its top and bottom. Take measurements at the top, and compare them to the measurements at the bottom. Taper causes the rings to travel in and out of their grooves as the piston travels up and down the cylinder.