C172 INCURS ON ACTIVE RWY AT SBA.

Narrative

I WAS ACTING AS PIC OF A FRIEND'S C172XP; WITH HER AS THE PNF. OUR TAXI INSTRUCTIONS FOR TKOF WERE TO TAXI ON RWY 33R; HOLD SHORT OF RWY 25; WITH TKOF TO BE FROM THAT INTXN ON RWY 25. AFTER RUN-UP; I TAXIED TO THE HOLD SHORT LINE AT RWY 25. THE ACFT HAD JUST HAD THE MASTER CYLINDER FOR THE BRAKES REPLACED; AND THE OWNER (THEN PNF) WAS SUGGESTING VARIOUS TESTS OF THE BRAKES; ASKING QUESTIONS ABOUT THE BRAKING AS WE TAXIED; AND IN GENERAL; WAS BEING A DISTR AS I APCHED THE HOLD SHORT LINE. AS I CAME TO A STOP; THE NOSE OF THE PLANE CROSSED OVER THE HOLD SHORT LINE BY ABOUT 2 FT; WITH THE NOSEWHEEL RESTING JUST OVER THE LINE. THE GND CTLR ASKED IF I WAS OVER THE LINE; I ADMITTED WE WERE; AND WAS TOLD TO DO A 360 DEG ON THE RWY AND THEN STOP BEHIND THE LINE. I COMPLIED; AND WAS THEN CLRED FOR THE INTXN TKOF. THERE WAS NO CONFLICTING TFC; AND NO ONE WAS ENDANGERED AT ANY TIME. THE PRINCIPLE CAUSE OF THE INCURSION WAS MY BECOMING DISTRACTED BY THE PNF; AND ALLOWING MYSELF TO GET 'BEHIND THE AIRPLANE.' OTHER MINOR CONTRIBUTING FACTORS WERE THE SLIGHTLY DIFFERENT FEEL OF THE BRAKES AFTER MAINT; THE UNUSUAL TAXI INSTRUCTIONS USING THE XING RWY; AND THE FADED PAINT OF THE HOLD SHORT LINE ACROSS RWY 33R.