HMM I WONDER IF SOMEONE PUT A 2.3 ROTOR IN, AND A 2.6 IMPELLER IN THE BLOCK, THE PINS YOU ARE REFERING TO ARE LOCATING PINS TO LOCATE THE FRT OF THE PMP HOUSING TO THE BLOCK, HOWEVER BEHIND THE SEAL THERE IS A RETURN HOLE AND SMALL PASSAGE CAST IN THE HOUSING THAT WILL LINE UP WITH A RETURN HOLE IN THE BLOCK, MAKE CERTAIN THIS PASSAGE IS NOT BLOCKED , OR IT WILL IMMEDIATELY BLOW THE SEAL RIGHT OUT OF THE BORE. PULL THE OIL PUMP OFF AND HOLD IT UP SIDE DOWN, WITH THE ROTOR POINTING UP, THE ROTOR SHOULD BE FLUSH AGAINST THE PMP BODY, NOW LAY THE IMPELLER FROM THE BLOCK OVER THE ROTOR AND IT SHOULD BE THE EXACT SAME HEIGHT AS THE ROTOR, WITH IN JUST A FEW THOUSANDS OF AN INCH ,INSTALLED CORRCTLY WITH THE CORRECT PARTS THE ROTOR WILL GO INTO THE BLOCK AND GO INTO THE PILOT HOLE JUST CLEARING THE BACK OF THE BORE , 5MM IS A LOT OF CLEARANCE . ONE OTHER THING MAKE CERTAIN THE ROLL PIN THAT GOES THRU THE ROTOR AND DRIVE SHAFT ISN,T BROKEN OR MISSING ,I HAVE NEVER SEEN THIS HAPPEN BUT ONE TIME IN A LOT OF YEARS BUT YOU NEVER KNOW . JERRY