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Thread: Installing CHT Probe Under Intake Flange Bolt

  1. #11

    Join Date
    Feb 2019
    Location
    Chandler, AZ
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    52

    Default Re: Installing CHT Probe Under Intake Flange Bolt

    Quote Originally Posted by Xengineguy View Post
    Build a stepped washer with one flat side to prevent it from turning. The id step protects the thermocouple
    from crush. Torque it down as normal.
    I've never used stepped washers. How would this work exactly? Wouldn't the thermocouple start spinning as soon as there is friction contact between it and the step washer?

  2. #12
    Senior Member PapuaPilot's Avatar
    Join Date
    Nov 2013
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    Nampa, Idaho
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    1,227

    Default Re: Installing CHT Probe Under Intake Flange Bolt

    Quote Originally Posted by AMK53 View Post
    I've never used stepped washers. How would this work exactly? Wouldn't the thermocouple start spinning as soon as there is friction contact between it and the step washer?
    I think it would get loose eventually and spin, which leads to a fluctuating reading on the gauge. I would do as others have suggested and get it sandwiched between washers using a high temp self locking nut. Check it for looseness each inspection and tighten if needed.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  3. #13

    Join Date
    Aug 2013
    Location
    Angola In
    Posts
    89

    Default Re: Installing CHT Probe Under Intake Flange Bolt

    Quote Originally Posted by AMK53 View Post
    I've never used stepped washers. How would this work exactly? Wouldn't the thermocouple start spinning as soon as there is friction contact between it and the step washer?
    Wish I could draw what I’m talking about. Think of a standard washer with the outer od large enough to
    cover the probe, plus some. Grind a flat on the od of the washer so you need to index it on installation.
    The flat keeps it from turning.
    Now think of the same washer with a step that fits the ID of the probe, thick enough to not quite extend all the way through. When you torque the probe down the probe tightens, then the step contacts the surface to protect the probe from over crush. Hope this make sense

  4. #14

    Join Date
    Feb 2019
    Location
    Chandler, AZ
    Posts
    52

    Default Re: Installing CHT Probe Under Intake Flange Bolt

    Thanks for all the advice. It looks like using a clipped oversized washer did the trick. It prevented the probe from being spun about its center axis and it stayed intact.

    CHT Probe Completed.jpg

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