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Thread: Piston replacement

  1. #1
    51-pa22's Avatar
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    Default Piston replacement

    I’m spit balling here so please help me understand something
    The thought is to change pistons from say 8.5:1 to 9.0:1 using AC 23-27 as guidance
    From section 6
    “6. ENGINE PARTS. You may install substitute/alternate engine parts for a part that is approved as original equipment or a PMA part for the engine installed on your aircraft in the following instance:
    a. The substitute/alternate part is PMA approved for a certificated engine,even if that engine is not the model approved for use on your aircraft model, and
    b. If the part is identical to (used on multiple engine models) the part for your engine model, or is listed as an approved substitute part by the engine manufacturer, then you may install the alternate part, and document the installation with only a logbook entry.
    Approval: This is a minor alteration and you may document it by a logbook entry. The logbook entry must reference the manufacturer's identification and industry specification for the original and replacement part.”
    Since Lycoming made O-320 engines from 7.00:1, 8.50:1 to 9.00:1 all things being equal could one use AC23-27 as approval to change out O-320-A1A (Wide Deck) 8.50:1 pistons to 9.00:1 pistons from the O-320-H1AD?
    Since Lycoming uses these PMAed 9:1 pistons in multiple certified engines and functions exactly as the original pistons with minor exceptions such as using 100LL fuel vs 91/96 avgas
    Last edited by 51-pa22; 07-28-2020 at 10:06 PM.

  2. #2
    Administrator Steve Pierce's Avatar
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    Default Re: Piston replacement

    Wasn't an H1AD and completly different engine/cylinders?

  3. #3
    51-pa22's Avatar
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    Default Re: Piston replacement

    Yes it is a different engine. As the section says...
    a. The substitute/alternate part is PMA approved for a certificated engine,even if that engine is not the model approved for use on your aircraft model, ...

    If it is a PMAed piston that will fit and operate
    And ...it is used on multiple engine models...

    You donít think it will pass the smell test as a way to 9:1 compression

  4. #4
    Administrator Steve Pierce's Avatar
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    Default Re: Piston replacement

    It is a modification of compression ratio. What data are you using to do the modification?

  5. #5
    Tailwind_Fan's Avatar
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    Default Re: Piston replacement

    I think the rub is in the section b ... identical, or approved substitute by the manufacturer.... ???

    I just purchased an O-320 E2A which is nominally a 7:1 compression ratio 150 hp motor, but it had an STC used to allow installation of 8:1 compression ratio pistons making it a nominally 160 hp motor. This was denoted by an additional tag added to the data plate.
    Last edited by Tailwind_Fan; 08-03-2020 at 04:10 PM.

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