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Old 01-20-2021, 12:44 PM
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avrojockey avrojockey is offline
Join Date: Aug 2019
Location: Appleton, WI
Posts: 352

Originally Posted by lr172 View Post
Was your case sent in during the overhaul? If so, they typically machine down the case to address the fretting. If orings are not used on the through studs, case fretting would allow oil to migrate into the stud clearance area, if present, and work out the case end. This is getting to an area where you need some expertise to determine how concerned you should be.

Thanks Larry...starting to understand now how oil can be migrating that way. On further review of record, the case was not sent out but locally cleaned, inspected dimensionally (I have all those dimensions - journals, clearances, bore alignments, etc) and NDT with dye penetrant, alodined and painted. The only things sent out (Aircraft Specialties, Tulsa) for inspection were major steel parts...crank, cam, tappets, all hardware, and accessory case gears and shafts. The cam and some tappets were later rejected and replaced.

There is no record of case being reworked for o-rings, and this is the only recorded overhaul of this case in 1993.

A case crack would make total sense but with fretting this is what I'm trying to understand..if fretting is the cause of this leak on a properly torqued case, then why would cases be modified to have a o-ring in the first place? Seems that is just putting a band-aid on the situation much as added Loctite 290 would be.

Thanks for all the help...Who would you recommend as far a professional advise, other than the A&P that does my condition inspection? Is there a particular engine shop I can talk to?
Tim Holmes
Appleton, WI
RV-9A N904DC
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