EMB135 CREW WAS REQUIRED TO SHUT DOWN #2 ENG BECAUSE OF AN INCORRECTLY INSTALLED GENERATOR.

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NIGHT WORK WAS PERFORMED ON #2 ENG OF ACFT. THE TASK WAS THE REMOVAL AND REPLACEMENT OF THE #4 GENERATOR DUE TO MEL PLACARD AND WRITE-UP; #4 GENERATOR BEARING FAIL MESSAGE. DURING THE REPLACEMENT OF THE GENERATOR; THE O-RING WAS IMPROPERLY INSTALLED. BEING A NEW MECH; (A FEW MONTHS ON THE JOB) I WAS TO WORK WITH AN INDIVIDUAL WHO HAD PERFORMED THE TASK PREVIOUSLY. ANOTHER MECH HAD ATTAINED THE PARTS FOR GENERATOR INSTALLATION. WHILE AT THE GATE; THE 2 OTHER MECHS WHO HAD DONE THE JOB PREVIOUSLY HAD GONE ON TO DO OTHER JOBS INSIDE THE AIRPLANE WHILE I DID MOST OF THE GENERATOR REMOVAL. I BELIEVE THE GENERATOR TASK WAS HANDED DOWN TO ME DUE TO THE FOUL WX THAT NIGHT; BEING COLD AND RAINING. BY THE TIME REMOVAL OF THE FAILED GENERATOR WAS ALMOST ACCOMPLISHED; THE OTHER MECHS WERE FINISHED WITH THEIR JOBS AND WERE GIVING ME A HAND. DURING INSTALLATION; ALL 3 MECHS WERE PRESENT; MYSELF; ANOTHER MECH HELPING THE INSTALLATION OF THE GENERATOR AND ANOTHER MECH SUPERVISING THE SIT. AT NO TIME DID I REALIZE THERE WAS A PROB WITH THE O-RING AND APPARENTLY NO OTHER MECH HAD REALIZED THE SIT. AFTER INSTALLATION; AN OP TEST WAS COMPLETED BY MYSELF AND ANOTHER MECH WHO HAD ENG RUN AUTH. WE HAD THE LOWER COWL OPEN DURING OPERATIONAL TESTS; THEN AGAIN NO PROB WAS DETECTED. THE FOLLOWING DAY; A PROB AROSE WITH THE GENERATOR; DUE TO IMPROPER INSTALLATION OF THE O-RING; WHICH LED TO THE #2 ENG BEING SHUT DOWN INFLT. THE FLT WAS DIVERTED MAKING AN EMER LNDG. I BELIEVE ALL PROBS COULD HAVE BEEN DISMISSED IF I HAD PAID CLOSER ATTN TO THE REMOVAL AND INSTALLATION PROCS. I SHOULD HAVE CHKED OFF ALL STEPS AS I HAD PERFORMED GENERATOR REMOVAL AND REPLACEMENT AND READ AGAIN THE PROCS AFTER I HAD FINISHED THE JOB; TO MAKE ABSOLUTELY SURE THAT ALL ASPECTS OF THE TASK WERE COVERED FULLY. FOR NOT DOING THIS; I HAVE MANY REGRETS AND HOPE THAT OTHERS MAY LEARN FROM MY MISTAKES AS I HAVE.