Disassembled my 20B yesterday that I purchased from JDM two years ago. Was so nice inside that I wish I hadnt even taken it apart. No rotor ridge, oil rings look brand new. Splitting the shaft was a non event. No tool or even a hammer. Just slid it right off. I loosened the front nut about two months ago. Maybe it being loose and the temp changes made it break loose. Were 90 one day and 30 the next for a month or so. Will start doing my porting Sunday.
Bob Mears