My ZDZ80 siezed in flight on Friday. Dead sticked it with minimal damage to the airframe.

The crankshaft would turn some, but with much friction. Took it home and after removing the cylinder head found the culprit - the C ring (retainer for wrist pin) on one side had come loose and was free in the cyinder!

Never had this happen before with any engine I have had.

Engine had about 20 gallons thru it, and about 18mo since purchase. Was running with 91octane and 50:1 Belray H1R.

Anybody lost a C ring on this engine before ??

Pic of piston attached