I have been told to watch out for the piston ring sets with the 3 piece oil rings. They carry a spring pressure of about 20 lbs. while what should be used is a spring pressure of about 7 to 9 lbs. This will act like it is honing the cylinder and wear it out in about 500 miles. It is better to use the 1 piece oil ring and get at least 5000 miles out of your mill.