Here’s a couple of answers and a few questions. You can’t use oversized rings unless you get an oversized piston. Second, you shouldn’t order any parts until you properly measure the bore to see if it is still in specs and not out of round. You need either a special gage or telescoping gages and a mic or calipers. Then to do so properly you do six different measurements. First, is 1/2” down in the same direction as the wristpin. Second, is in the center of piston travel and the third is 1/2” from the bottom of the cylinder. Then you take the same three more measurements 90 degrees from the first three. With these six measurements you can accurately tell if the cylinder is in specs and not out of round. Pistons from a CV15 are different than the CV13. Your crankshaft has the same crankshaft number as a BASIC CV15, but you will need the spec number from the 15, as they may have changed the crank. You say the cylinder needed work and the rings were bad. I suspect that the piston lands and grooves may be bad also. Would be a good idea to check it against the specs in the manual. To me this looks like an expensive project, unless you love the engine and unit. Ask yourself, “Is the cost worth the effort and possible failure.”
