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Old 01-21-2021, 09:08 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Originally Posted by avrojockey View Post
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?
I would call Divco. They are the experts and likely to provide some guidance. I am not sure if case fretting or stud / bore wear could cause a leak here, but guessing they can if no oring is installed and I am just not sure if they are used on all or some cases. I would not expect fretting or bore wear to cause leakage if o-rings are used (no way for the oil to get out). I am pretty sure that I read that the o-rings channels are not universal, but shops like Divco will put them in when they re-work a case. I just can't recall the details; It may have been the locking sleeves that I am thinking of that help to prevent fretting and not o-rings. A bad o-ring certainly could cause leakage, but doubt they would go bad, even in 20 years. My big concern here is a case crack, that definately could cause this if the crack lead to the stud bore and expect many web cracks would, as that is one of the weak points in the web. Divco can share their experiences in this regard.

If you confirm that you have o-rings, I would be thinking case crack as the culprit.

Before going down this path, I would be absolutely sure that is where the oil is originating. If that is where it is coming from, DO NOT address this with loctite or other sealant, as a pretty likely cause is a significant case crack and that is not a problem you want to just cover up with sealant, at least not without expert guidance. That being said, the case can go a long time with some types of cracks. Divco told me it is not common to get a 540 case in for re-work that does not have at least one crack in the webbing. However, not all webbing cracks are equal when it comes to structural integrity.
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Last edited by lr172 : 01-21-2021 at 09:26 AM.
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