GA SMA ENGINE QUIT WHILE IN CRUISE FLT. PLT DIVERTED TO ALTERNATE ARPT.

Narrative

I WAS ENRTE IFR CLRNC FROM MANSFIELD; OHIO WERE TO STL; MO; RNAV DIRECT IN MY SMA. THE WX CONDITIONS OF FLT WAS VFR; 15 MI VIS; OCCASIONAL LIGHT PRECIPITATION AND HIGH PRESSURE DOMINATING THE ENTIRE ROUTE OF FLT. THE ACFT WAS IN CRUISE 1 HR AND 32 MINS IN FLT WHEN I ENCOUNTERED ENG FAILURE. THE GAUGES INDICATED NO PROB OF OIL PRESSURE; TEMP; CHT AND EGT. THE INSIGHT ENG COMPUTER SHOWED NO SIGN OF INJECTION PROBS. AT THIS TIME I NAVIGATED LORAN DIRECT TO 35M 10.4 MI AWAY. I ATTEMPTED AN ENG RESTART AT 5500' MSL; BUT THE ENG WOULD NOT STAY RUNNING. I ENTERED THE PATTERN AT 3000' MSL ABOVE THE ARPT AND RADIOED MY INTENTIONS ON 122.8 TO LCL TFC. I LANDED THE ACFT SAFELY AND ROLLED TO THE PARKING RAMP. UPON VISUAL INSPECTION OF THE ACFT; THERE WAS A LOT OF WATER DRIPPING FROM THE COWL FLAP AREA. AFTER INSPECTION; IT APPEARED THAT THE RAM AIR CTL KNOB LOCK TAB WAS WORN AND WOULD PARTLY OPEN IN FLT WHEN VIBRATION WAS INCREASED FROM SLOWING DOWN THE PROP. THE PARTIAL OPENING OF THE RAM AIR KNOB IN FLT WITH THE PRESENCE OF MOISTURE CAUSED THE ENG TO QUIT. THE CORRECTIVE ACTION TAKEN WAS TO BEND THE TAB DOWN WITH A PAIR OF PLIERS TO PREVENT THE RAM AIR FROM OPENING IN FLT. I AM ORDERING A NEW LOCKING TAB FOR THE RAM AIR KNOB AND SHOULD HAVE IT INSTALLED IN 1 WK. I AM ALSO PREPARING TO TAKE MY INSTRUMENT CHK FOR MY LICENSE. I HAVE BEEN FLING WITH MY CFII FOR 3 MONTHS. I FEEL SAFER IN THE SYS TALKING TO ATC AT ALT WITH TFC ADVISORIES.