In about 400hrs the closest I've come to complete engine failures.....
Engine suddenly stopped completely during aerobatics in a Firefly; probably fuel flow interruption caused by a very rapid attitude change. Hitting the start button while diving towards the ground restarted it almost immediately though.
Two partial losses of power in a Super Cub; first time the engine gradually lost power before stabilising at about 1800rpm.....instructor reckoned a cylinder or two may have stopped working but examination on the ground could reveal no problem and after starting up again it produced normal power. Second time some sort of problem with the carb heat was causing a 500rpm drop on application. About a year later the aircraft suffered a complete engine failure on take off probably due to carb icing (possibly having built up on the ground); this time someone else was flying it though.
Only other incident which could have turned into an engine failure was when I started the engines on the Twin Comanche not realising that the supposedly inop and empty tip tanks were engaged on one side; the engine ran for about a minute before just running down from lack of fuel. If there had been more residual fuel in the lines and I hadn't done any power checks the engine could have decided to go during the take off roll.....which wouldn't have been funny.