LIGHT ACFT MAKES FORCED LNDG IN OJC AIRSPACE DUE TO ENG FAILURE.

Narrative

RETURNING FROM THE PRACTICE AREA; WE SELECTED AN EMER LNDG AREA AND DSNDED FROM 3500 FT TO 2000 FT MSL (1000 FT AGL) TO PRACTICE A RECTANGULAR PATTERN. ENTERING THE MANEUVER DOWNWIND; THE ENG LOST PWR; BEGAN SHAKING AND RUNNING VERY ROUGH. I TOOK CTL AND SET UP FOR AN EMER LNDG. WE CALLED OJC TWR; ADVISED OUR POS AND INTENTIONS TO LAND IN THE GRASS PASTURE. THE APCH AND LNDG WAS UNEVENTFUL -- NO DAMAGE AND NO INJURIES. THE ENG HAD BLOWN A CYLINDER DUE TO A FROZEN VALVE. IF WE HAD TRIED TO MAKE THE ARPT; I FELT THE ENG MIGHT HAVE STARTED TO COME APART. IT PRODUCED 1300-1400 RPM AND THERE WAS NO INDICATION OF SMOKE; OIL OR FIRE; YET I HAD ALREADY PICKED A GOOD FIELD; SO WE LANDED SAFELY. THERE WAS NO QUESTION IN MY MIND THAT WE WOULD TRY TO ATTEMPT THE RWY; 6 MI N OF US. I THINK IT'S IMPORTANT TO ALWAYS THINK OF THE TERRAIN BENEATH THE ACFT AND LOCATE A GOOD LNDG AREA PRIOR TO DSCNT. THE OUTCOME COULD EASILY HAVE BEEN DIFFERENT IF WE HAD NOT PLANNED FOR THE POSSIBLE EMER BEFORE WE EVEN TOOK OFF. THIS WAS MY FIRST ACTUAL ENG FAILURE IN 25 YRS OF FLYING. IT IS DIFFERENT; BUT REPETITIVE TRAINING ALLOWED ME TO EASILY GLIDE THE ACFT TO A SAFE STOP.