RE: OS SF ABC advice?
OS changed the way they applied the plating to their liners when they went to the 'RF/SF' engines. Initially, there were some serious 'peeling' problems with the ABC liners (OS never plated with chrome and I don't believe YS did either). I know I had 2 that 'peeled' with less than 50 flights (no lean runs - I thought the bearings had failed; they had, because the liner peelings ruined them) and even the big names had problems (Ivan Kristensen had to send a couple engines back). OS was really good about replacing the piston/sleeves that went bad. The later engines including the Hanno Specials (MKI and MKII) were much better, you could expect 350 to maybe 1000 flights. However, Dave Shadel started marketing true 'ABC' replacement liners/pistons (made by Henry Nelson) for the original OS 61RF which had much more aggressive porting (about 500rpm more than stock) and terrific durability. They also provided them for the Hanno with the same 'Hanno' porting; so the same power, but much better durability. For me, stock OS liners last between 350-800 flights. I had one OS 61RF-abc-p which had more than 1600 flights on the Nelson parts. There was no sign of peeling, just wear as the brass was starting to appear.
Henry Nelson is more or less retired, but when I last spoke with him (about a year ago) he still had some piston/sleeve assemblies for side and rear exhaust OS 61s.
-Will