Guess as to Origin of Metal Found in Oil Screen

Discussion in 'Maintenance Bay' started by iflyvfr, Jul 26, 2020.

  1. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    The old man used to share a hanger with a buddy who ran a one man/one airplane flight school. When my sister decided to get her ticket, the old man wouldn't let her fly in Mack's airplane because he had seen Mack's A&P working on it.
     
  2. Kenny Phillips

    Kenny Phillips En-Route

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    Looks more like baked-on oil than anodizing.
     
  3. MuseChaser

    MuseChaser Pattern Altitude

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    Could it be something that might have fallen off the mechanic's workbench/table/area into the oil screen once it was removed from the plane, or dislodged from elsewhere in the engine bay and fell into the screen AS it was being removed... maybe not anything from within this engine at all? Stranger things have been known to happen, especially in a busy shop with lots of projects going on at once.
     
  4. iflyvfr

    iflyvfr Pattern Altitude

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    I'm going to call him tomorrow or stop by this weekend to see where it came from. I'm betting a piston but am not willing to put money on it. Just interesting, scary, and educational all at once.
     
  5. JAWS

    JAWS Cleared for Takeoff

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    Drain the oil and run a boroscope through the case.
     
  6. NordicDave

    NordicDave Pattern Altitude

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    :yeahthat::yeahthat::yeahthat:

    Then dismount the engine and send it off for tear down & analysis by a quality engine shop.
     
  7. weilke

    weilke Touchdown! Greaser! PoA Supporter

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    Or if you have time, take it apart yourself, find the donor site. Then find a new case, send off the good bits for NDT and machining. Then find a 'P' mechanic who can put it all back together and sign off the repair.
     
  8. painless

    painless Pre-takeoff checklist

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    :yeahthat::yeahthat:

    Or just replace the engine with an O 320.
     
  9. weilke

    weilke Touchdown! Greaser! PoA Supporter

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    Or that. I dont know where prices for the older 172s are, but doing that could easily put that plane into a bracket where you can never sell it anywhere close to what you have into it. Otoh, the cost to a teardown & repair when all you have to pay for are the send-out services and the labor to your assembler may make that repair of an older 172 economically viable.
     
  10. NordicDave

    NordicDave Pattern Altitude

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    That's an interesting idea.
     
  11. Dan Thomas

    Dan Thomas Final Approach

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    If it's just a chunk off the bottom of a piston that was clumsily installed in the cylinder, with the oil ring catching on the edge of the bore and some guy thumping on it with his rubber hammer and cracking it, there might be nothing else wrong at all with the engine. A new piston with the old rings might fix it all up. The chunk of piston could have fallen into the sump and stayed there and caused no other damage.
     
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  12. Dan Thomas

    Dan Thomas Final Approach

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    No. An intere$ting idea.
     
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  13. NordicDave

    NordicDave Pattern Altitude

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    LOL!
     
  14. NordicDave

    NordicDave Pattern Altitude

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    All seriousness that a pretty good idea except for putting old rings on a new piston. The rings must be gaped to the piston and they also wear together.

    If it were my plane I'd pull cylinders until I found the offending piston. In fact I'd pull the whole top end off for easy borescope inspection for damage and assess if the damaged piston and cylinder could be replaced to solve the problem. Also thoroughly cleaning the oil pan for debris is advised.
     
  15. Dan Thomas

    Dan Thomas Final Approach

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    Rings are gapped to the cylinder.
     
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  16. NordicDave

    NordicDave Pattern Altitude

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    Yes.

    I have not worked on an O-300, but there are similarities with the larger bore Continentals. The cylinder barrel needs to be measured for service limit concentrically and inspected for wear. Ring gaps are measured on the piston while in the bore at a set location. TCM usually specifies an 1/2-1" from the top.

    If it were mine, and a cylinder needed repair I'd send an offending Cylinder out for overhaul or IRAN as warranted.
     
    Last edited: Jul 29, 2020
  17. mondtster

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    The end gaps are not measured on the piston. You put the rings in the bore at the specified location and check what the gaps are.

    I would not be the least bit scared of reusing piston rings that are in good condition. I wouldn’t even bother to check end gap. In many (All?) engine manufacturing shops the rI guess end gap is never even checked. In the engine test lab in which I work there have been zero gaps checked and we put thousands of pistons in cylinders every year.

    All that said, if installing new piston rings in an aircraft cylinder they MUST be checked. I have no idea how many engines I’ve assembled now but I have never run across a new aircraft engine piston ring that didn’t need to be filed.
     
  18. NordicDave

    NordicDave Pattern Altitude

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    Yes, and need to correct myself from previous post. Got distracted multitasking. There is no feeler gauge I’m aware of to measure ring gap on the piston in the bore. The ring is measured within the top 1/2”-1” of the bore and placed on the piston to check for fit.
     
  19. mondtster

    mondtster En-Route

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    How to check the end gaps is something that should be done via the overhaul manual for the specific engine (I'm sure you know this and will agree). Some aircraft engine cylinders have choked bores and some are straight. In a choked bore the instructions generally are to set ring end gap in the straight portion of the bore and check it in the choked section, at the top of its travel, to insure that the minimum clearance requirements are met. With the straight bores it obviously doesn't matter where the ring is placed to check/set the clearance. :)
     
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  20. imwithtuxedo

    imwithtuxedo Pre-takeoff checklist

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    That is simply accumulated carbon deposits. Fly it for 10 hrs and recheck the screen.





    ps: don't do this ^^^^^^^
     
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  21. Daleandee

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    My brother was working at an Oldsmobile dealership and said one of the things other mechanics liked to do when someone was installing an engine they had rebuilt was to wait till they went to lunch and then set something like another oil pickup tube on the workbench among the parts. You had to be sure you put everything back together correctly or you'd end up pulling the engine back out to get the pan off and see if you had really put the oil pickup on the engine. Sounds really funny till it happens to you ... :D
     
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  22. MuseChaser

    MuseChaser Pattern Altitude

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    I liked the scene in "Ford vs Ferrari" when Matt Damon as Caroll Shelby tossed a nut (or bolt?.?..don't remember) into the Ferrari pit.....
     
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  23. Dan Thomas

    Dan Thomas Final Approach

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    There IS a spec for ring-to-land clearance, but it would take a battered old piston to exceed the spec.
     
  24. iflyvfr

    iflyvfr Pattern Altitude

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    I used speed tape and some new rings, currently flying off the hours using mineral...:D
     
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