A PIPER 31-350 DURING A ROUTINE INSPECTION WAS FOUND TO HAVE BULGING UPPER WING SKIN INBOARD OF ENG NACELLE; DETERIORATED UP STOP BUMPERS AND A CRACKED WHEEL WELL WING RIB STATION 49.

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DURING ROUTINE INSPECTION; FOUND VISUAL BULGING OF SKIN ON UPPER WING'S INBD OF ENG NECELLE; UPON FURTHER INSPECTION FOUND; RUBBER UP STOP MTS STARTING TO DRY ROT. AT A SMALL CRACK ON ADJACENT WITH WELL RIB AT WING STA #49.0. AT THIS TIME; ACFT OWNER WAS GOING TO DO AN S.T.C. THAT WOULD CHANGE THE TOTAL GROSS WT OF THE AIRCRAFT AND ORDERED THE KIT FROM ABC WING MODIFICATION CO XXX; US. UPON READING THEIR MATERIALS I CALLED THEM AND SPOKE TO ONE OF THEIR MECHANICS; HE EXPLAINED TO ME HOW TO REPAIR THE SKIN AND FRAME/RIB AND THAT THE REPAIR WAS OF A MINOR REPAIR AND LOG BOOK SIGN OFF ONLY. THIS IS WHAT I DID. I REPLACED THE RUBBER MTS AND DID A GEAR EXTENSION; EVERYTHING CHKED AND NORMAL AND I SIGNED IT OFF. AT THE NEXT ROUTINE INSPECTION MTC FOUND A CRACK AT THE END OF THE DOUBLER REPAIR I INSTALLED. UPON MY INSPECTION I REALIZED THE HYD-MULE WAS NOT GIVING ME THE HYD PRESSURE; THAT THE ENGS GIVE. ALLOWING THE GEAR RETRACTION TO COME UP VERY SMOOTHLY AND LOCKING. AFTER THINKING OF THIS; IT MAY BE OF A MAJOR REPAIR AND REQUIRE FIELD APPROVAL. I BELIEVE THE HYD-MULE USED IN THIS SIT DOES NOT PRODUCE ENOUGH PRESSURE TO DO THE JOB PROPERLY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAUSE OF THE UPPER WING SKIN BULGING AND THE RIB CRACK WAS BELIEVED TO BE ROTTED UP STOP RUBBER GEAR BUMPERS. THE RPTR SAID THE UP STOP BUMPERS WERE A .250 INCH THICK RUBBER PAD ABOUT 4 INCHES LONG AND HAD COMPLETELY DETERIORATED ALLOWING THE LNDG GEAR ON RETRACTION TO STRIKE THE UPPER WING SKIN. THE RPTR STATED THE PADS WERE REPLACED AND THE RIB CRACK AND UPPER WING SKIN WAS REPAIRED. THE RPTR STATED THE LNDG GEAR WAS OPERATED WITH A HANGAR HYD-MULE AND CHKED NORMALLY. THE RPTR STATED A LATER ROUTINE INSPECTION REVEALED THE REPAIRED RIB WAS AGAIN FOUND CRACKED. THE RPTR STATED TO THE BEST OF HIS KNOWLEDGE NO AIRWORTHINESS DIRECTIVE EXISTS ON THIS WHEEL WELL RIB CRACK SIT. THE RPTR SAID THE ADJUSTMENT AND INSPECTION OF THE OP OF THE LNDG GEAR MAY NOT HAVE BEEN ACCURATE SINCE THE HANGAR HYD-MULE DOES NOT SUPPLY THE HIGHER PRESSURE OF AN ENG DRIVEN HYD PUMP.