Timing chain tension

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Austin Longenecker, Apr 9, 2025.

  1. Austin Longenecker

    Austin Longenecker Member

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    Unfortunately, it is my turn to replace my head gasket. I've been working with an experienced mechanic who pointed out that the timing chain is loose. Not to the point of jumping a sproket, but upon a visual inspection, the timing chain does have some sag at the top. I'm wondering if it's better to replace the chain or to simply adjust the tensioner to keep the chain tight. I guess my real question is, has anybody ever had the timing chain in their Prius fail?

    2010 Prius, 250K miles.

    Posted via the PriusChat mobile app.
     
    #1 Austin Longenecker, Apr 9, 2025
  2. BiomedO1

    BiomedO1 Senior Member

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    Timing chain failures are rare; but they do happen. I believe the tensioner is self-adjusting; wouldn't recommend shimming it or something. The chain needs to be measured to see if it's still within tolerances. To quote Clint Eastwood; "Are you feeling lucky?".:love:

    FWIW; Since it's apart; I'd clean out the EGR, replace the valve stem seals, water pump, and thermostat too; so that all your hard work doesn't go to waste by short-cutting the job.

    Just my 2-cents......
     
    #2 BiomedO1, Apr 9, 2025
    CR94 likes this.
  3. CR94

    CR94 Senior Member

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    Did you check the tensioner? If it's free and functioning properly, and the guides are ok, I don't see how the chain could be loose unless it's badly worn ("stretched").
     
    #3 CR94, Apr 10, 2025
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    Last link in my signature is Repair Manual engine section, has timing chain specs. (On a phone turn it landscape to see signatures)
     
    #4 Mendel Leisk, Apr 10, 2025
  5. ASRDogman

    ASRDogman Senior Member

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    There's sag at the top, between the two sprockets, because you put in on incorrectly.
    You'll have to put the #1 piston at tdc, remove the timing chain and install it correctly.

     
    #5 ASRDogman, Apr 10, 2025
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    Good video on the chain install:

     
    #6 Mendel Leisk, Apr 10, 2025
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