Narrative:

I am an airframe power plant mechanic operating a maintenance facility. After a sudden stoppage of 2 'O 320' engines a customer brought the disassembled engines to my shop for repair. The customer had disassembled the engines in an effort to reduce cost. I agreed to reassemble the engines with all parts; supplies and inspection cost being paid directly by the customer. All parts used were verified as being svcable lycoming type parts. Ipm; service bulletins and ohm were used. Near completion of the engines it was discovered that these engines were 'O 320 A3B' and not 'O 320 B3B.' this meant that the wrong pistons with wrist pins had been used. When asked; the customer indicated he had or would have the stc for this upgrade. Upon completion of the engines; the customer (not satisfied with a logbook entry) tore one out of the log and I replaced it with a more agreeable entry. I was concerned about the stc or any approval for the 8.5:1 pistons and upon not receiving any confirmation on the approval; I felt I must have answers prior to the aircraft flying with those modified engines. It was confirmed by company engine services that svcable pistons and pins were purchased by the customer and were not part of the original engine. I decided to research the effects these pistons and pins would have an 'O 320 A3B' engines. The only differences noted were the piston; pin and the use of straight bore cylinders on the 'O 320 A3B.' still my advice to the customer was and is to replace the pistons and pins with the lower compression pistons as little advantage would be noted in comparison to the paperwork and time needed to approve this modification. It is now policy to thoroughly examine the engine logbook prior to any assembly. This is to verify that the engine designation is not compromised by incorrect modification. Although it is believed this modification would not cause a safety issue; as of this date this modification has not been approved by any agency.

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Original NASA ASRS Text

Title: A PA23-150 ACFT WITH O-320-A3B ENGINES HAD CYLINDER PISTONS AND WRIST PINS INSTALLED THAT WERE FOR O-320-B3B TYPE ENGINES.

Narrative: I AM AN AIRFRAME PWR PLANT MECH OPERATING A MAINT FACILITY. AFTER A SUDDEN STOPPAGE OF 2 'O 320' ENGS A CUSTOMER BROUGHT THE DISASSEMBLED ENGS TO MY SHOP FOR REPAIR. THE CUSTOMER HAD DISASSEMBLED THE ENGS IN AN EFFORT TO REDUCE COST. I AGREED TO REASSEMBLE THE ENGS WITH ALL PARTS; SUPPLIES AND INSPECTION COST BEING PAID DIRECTLY BY THE CUSTOMER. ALL PARTS USED WERE VERIFIED AS BEING SVCABLE LYCOMING TYPE PARTS. IPM; SVC BULLETINS AND OHM WERE USED. NEAR COMPLETION OF THE ENGS IT WAS DISCOVERED THAT THESE ENGS WERE 'O 320 A3B' AND NOT 'O 320 B3B.' THIS MEANT THAT THE WRONG PISTONS WITH WRIST PINS HAD BEEN USED. WHEN ASKED; THE CUSTOMER INDICATED HE HAD OR WOULD HAVE THE STC FOR THIS UPGRADE. UPON COMPLETION OF THE ENGS; THE CUSTOMER (NOT SATISFIED WITH A LOGBOOK ENTRY) TORE ONE OUT OF THE LOG AND I REPLACED IT WITH A MORE AGREEABLE ENTRY. I WAS CONCERNED ABOUT THE STC OR ANY APPROVAL FOR THE 8.5:1 PISTONS AND UPON NOT RECEIVING ANY CONFIRMATION ON THE APPROVAL; I FELT I MUST HAVE ANSWERS PRIOR TO THE ACFT FLYING WITH THOSE MODIFIED ENGS. IT WAS CONFIRMED BY COMPANY ENG SVCS THAT SVCABLE PISTONS AND PINS WERE PURCHASED BY THE CUSTOMER AND WERE NOT PART OF THE ORIGINAL ENG. I DECIDED TO RESEARCH THE EFFECTS THESE PISTONS AND PINS WOULD HAVE AN 'O 320 A3B' ENGS. THE ONLY DIFFERENCES NOTED WERE THE PISTON; PIN AND THE USE OF STRAIGHT BORE CYLINDERS ON THE 'O 320 A3B.' STILL MY ADVICE TO THE CUSTOMER WAS AND IS TO REPLACE THE PISTONS AND PINS WITH THE LOWER COMPRESSION PISTONS AS LITTLE ADVANTAGE WOULD BE NOTED IN COMPARISON TO THE PAPERWORK AND TIME NEEDED TO APPROVE THIS MODIFICATION. IT IS NOW POLICY TO THOROUGHLY EXAMINE THE ENG LOGBOOK PRIOR TO ANY ASSEMBLY. THIS IS TO VERIFY THAT THE ENG DESIGNATION IS NOT COMPROMISED BY INCORRECT MODIFICATION. ALTHOUGH IT IS BELIEVED THIS MODIFICATION WOULD NOT CAUSE A SAFETY ISSUE; AS OF THIS DATE THIS MODIFICATION HAS NOT BEEN APPROVED BY ANY AGENCY.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.