A CESSNA 150 AFTER COMPLETION OF THE ANNUAL INSPECTION AND RELEASE FOR SVC INSPECTOR DISCOVERED INCORRECT ENG WAS INSTALLED.

Narrative

I SIGNED OUT AN 'ANNUAL' ON THE FOLLOWING ACFT BASED AT ZZZ. CESSNA 150G ON EDO 1650 FLOATS; EQUIPPED WITH STC (INSTALLATION OF LYCOMING 0-290-D2 AND PROP); COMPLETED WITH FORM 337. AFTER THE ANNUAL WAS COMPLETED FOR THE OWNER; COMPANY X; THIS ACFT WAS SOLD TO ANOTHER PERSON OR CORPORATION. THIS NEW OWNER APPARENTLY APCHED A LCL HOMEBUILDER; MR. Y (NOT A LICENSED AME OR A & P/IA) TO DO SOME UNSPECIFIED WORK ON THE ACFT. ALTHOUGH NOT A CERTIFICATED MAINT TECHNICIAN; THIS PERSON IS KNOWLEDGEABLE ABOUT EARLY VINTAGE LYCOMING ENGINES AND AFTER LOOKING AT THE ENG ON THE ACFT REPORTED TO ME TODAY THAT THE ENG AND ENG DATA PLATE DO NOT AGREE. HE SAID THAT THE DATA PLATE SERIAL NUMBER AND THE FACT THE ENGINE HAD A 'DYNAFOCAL' ENGINE MOUNT LEAD HIM TO PHONE LYCOMING. HE MAINTAINS THAT THE ENG IS 'ILLEGAL.' AFTER TALKING TO THE FAA INSPECTOR AND DOING SOME MORE RESEARCH ON THE ACFT; IT BECAME APPARENT TO ME THAT THE ORIGINAL INSTALLATION OF STC (INSTALLATION OF AN ALTERNATE LYCOMING -290 ENG MANY YEARS BEFORE MAY HAVE BEEN AN IMPROPER USE OF THE STC WHICH WAS LIMITED TO A SINGLE ACFT SERIAL NUMBER. IF THIS IS THE CASE; I APPARENTLY SIGNED OUT AN 'ANNUAL' ON THIS ACFT AS AIRWORTHY WITHOUT DETECTING AN IMPROPER ENG INSTALLATION.