I just bought my second jato with a 2.5 in it. They are both well used but in really excellent shape. One is a 2.5R the other is a plain 2.5, what is the difference between the 2???? Also the plain 2.5 doesn't idle after running for a few minutes and dies, I figured its losing compression when it warms up but not sure. How can you tell when a motor is worn out, and is it hard to replace the piston and sleeve?