I have an engine that appears to be identical to the one originally posted. It is a 21cc and originally came with roller bearings on the front and rear. The case castings appear to have been made with the option for ball bearings, so I bored out the front and anstalled a standard ball bearing ( 10mm X 32mm X 7mm) I left the rear roller bearing in as I didn' see the need to change it with the ball bearing on the front of the case to take the thrust. I also cut 60 thousands from the base of the cylinder and changed the exhaust and intake ports consistent with the info given in " Don't forget Echo". I used a ball end mill to raise the ports 40 thousands to compensate for the material removal from the base of the cylinder. The piston top was reshaped to give 15 thousands clearance between the piston and cylinder head. A CH syncro spark was used and the timing set at 30 deg BTDC. It also has a new Frank Bowman ring.

Performance isn't quite what I expected, but it does turn a 15 X 6 APC at 8500 rpm. I haven't played with any other props at this time, but It has only 15 to 20 minutes of run time on the new ring.