A C172 PLT SMELLS SMOKE INFLT RESULTING IN AN EMER LNDG.

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I WAS FLYING AT 9000 FT ON AN IFR FLT PLAN; RYY TO ROA. ROA IS MY HOME FIELD; BUT I'VE BEEN ON AN EXTENDED BUSINESS TRIP FOR SEVERAL MONTHS NEAR RYY. IT WAS VERY CLR AND SMOOTH ON THIS NIGHT. I THOUGHT I SMELLED A WHIFF OF SMOKE; BUT COULDN'T IDENT IT SO I DECLARED AN EMER AND ASKED TO DIVERT TO HKY WHICH WAS ABOUT 5 MI TO THE R OF MY CURRENT TRACK. ZTL CLRED ME DIRECT TO HKY AND HANDED ME OFF TO THE TWR WHICH CLRED ME TO LAND ON ANY RWY. LANDED RWY 24 WITHOUT INCIDENT. I DID NOT NOTICE ANY FURTHER INDICATION OF SMOKE WHILE DIVERTING TO HKY; DURING LNDG OR TAXI. TAXIED TO THE FBO; SHUT DOWN AND FILLED OUT THE FIREMAN'S PAPERWORK. THE FBO LINEMAN HELPED PUSH THE AIRPLANE INTO AN OPEN HANGAR WITH SOME LIGHTING. I REMOVED THE COWLING AND INSPECTED ALL THE HOSES AND WIRING FOR LEAKS OR LOOSENESS OR SIGNS OF ANYTHING THAT MIGHT CAUSE A SMOKE SMELL AND FOUND NOTHING. REPLACED THE COWLING; PERFORMED A RUN-UP AND A SYS CHK OF EACH COMPONENT. FOUND NO ANOMALIES; NO EVIDENCE OF SMOKE. ALL EQUIP APPEARED CORRECT. SPENT THE NIGHT; AND FROM MY HOTEL; CALLED MY MECH TO DISCUSS WHAT FURTHER CHKS MIGHT BE APPROPRIATE. NEXT MORNING I HIKED TO THE HARDWARE STORE AND PURCHASED A VOLTMETER TO CHK FOR OVER OR UNDER VOLTAGE ON THE ACFT. RETURNED TO THE FBO; REMOVED THE COWLING AND REEXAMINED ALL WIRING AND HOSES AND BATTERY; BUT FOUND NO ANOMALIES OR EVIDENCE OF SMOKE. REPLACED COWLING; PERFORMED A RUN-UP AND TRIED EACH SYS INDIVIDUALLY AND TOGETHER. ALL EQUIP APPEARED CORRECT AND FUNCTIONAL. CHKED VOLTAGE AT CIGARETTE LIGHTER AND FOUND IT TO BE CORRECT AT IDLE AND RUN-UP. NO EVIDENCE OF SMOKE OR SMOKE ODOR WAS FOUND. DECIDED THAT ACFT WAS SAFE TO FLY; SO CONTINUED ON TO ROA. MY MECH PULLED THE ALTERNATOR AND FOUND THE BATTERY TERMINAL TO BE BURNED ABOUT HALFWAY THROUGH FROM ARCING. THIS HAD BEEN 'EXAMINED AND CORRECTED' BY A MECH AT RYY A FEW WKS EARLIER WITH NO MENTION OF A BURNED TERMINAL. I DON'T KNOW IF IT BURNED FURTHER DURING THIS FLT. I PRESUME THAT; SINCE PIC IS THE FINAL AUTH ON THE SAFE OUTCOME OF THE FLT; IF A MECH AT HKY SHOULD HAVE BEEN CALLED TO EXAMINE THE ACFT PRIOR TO CONTINUING ON TO ROA. IT WAS FRIDAY NIGHT AND A MECH WOULD NEXT BE AVAILABLE ON MONDAY. ALSO; WOULD THE MECH AT HKY BE ANY BETTER THAN THE MECH AT RYY? THERE IS VALUE IN FINDING A MECH; WHO KNOWS YOUR AIRPLANE AND EARNS YOUR TRUST.