Check the tech tips page for my procedure for checking cylinder taper with a used piston ring and a feeler gauge- - - -no inside micrometer needed. Square up a piston ring pulled up snug against the ring ridge, and measure the gap by stacking up feeler gauge blades until they fill the gap. Add up the blade thicknesses and record the total reading. Now push the ring down near the bottom of the ring travel with a piston and measure the gap again- - - -it should be considerably smaller. Calculator time- - - -subtract the bottom reading from the top measurement. Divide the difference by 3.14 (Pi). The result is the cylinder taper in thousandths of an inch. If it's over .005", you probably need to rebore the cylinders. A stovebolt block can handle a 60 over bore with no problem, and 80 is a bit marginal, but lots of them are running around that way. At 2000 RPM, a ring in a taper-worn cylinder is flexing 60 times a second trying to keep up with the changing bore size from top to bottom. That makes rings lose their tension in a hurry. Boring eliminates the taper, and practically all of the ring flex.
Jerry
