I overtorqued my head bolts, what should I do?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Higgins909, Jun 29, 2026.

  1. Higgins909

    Higgins909 Member

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    It turns out I can’t read a torque wrench and ended up doing 46# instead of the 36# it calls for (iirc). Then I did the 90 and then the 45 angles by eye, with a paint marker.

    I'm wondering how bad I messed up and what the solution is.

    I figured this out when I stretched out one of the Cam Assembly Gold Bolts. Almost broke it off in the head. I’m not worried about that though.

    just the head bolts. Since it’s still apart, should I retorque them or send it and expect the bolts to stretch a bit?

    reading online, some said new bolts and gasket but I didn’t overtorque nearly as much as they did.
     
    #1 Higgins909, Jun 29, 2026
  2. PriusCamper

    PriusCamper Senior Member

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    Well... Torque spec is designed for maximum strength, so they could be weaker, but maybe close enough? If I were you I'd back off them 1/8th turn or less and call it done. I think it problematic loosening them more than that if the bolts got stretched... Of course if you want to be more thorough you could remove one of the bolts and do the test to determine if they've been stretched beyond spec and need to be replaced.
     
    #2 PriusCamper, Jun 29, 2026
  3. rjparker

    rjparker Tu Humilde Sirviente

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    I have seen incorrectly torqued head bolts blow a new gasket in weeks. I would either leave them alone and hope, or pull them off, change the hg and use new head bolts.

    I certainly would not loosen them just a bit. I suppose you could pull it apart, replace the hg and measure each bolt, but I doubt I would do that.

    IMG_1966.jpeg
     
    #3 rjparker, Jun 29, 2026
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  4. PriusCamper

    PriusCamper Senior Member

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    Pretty sure @Mendel Leisk can explain/link to the bolt stretch test...
     
    #4 PriusCamper, Jun 29, 2026
  5. Higgins909

    Higgins909 Member

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    I visually compared the old to the new head bolts and though they had to of been within 0.050" of each other. I was hoping it was a minor over torque and it would "probably" be ok. I was really hoping to not have to buy a 2nd head gasket and set of bolts.

    Edit:I haven't taken anything apart yet. Waiting on my replacement bolts for the cam assembly.
     
    #5 Higgins909, Jun 29, 2026
  6. PTS

    PTS Member

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    In post three it shows the maximum length allowed. It is not about how close they are to each other.
     
    #6 PTS, Jun 29, 2026
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  7. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Last link in my signature is the full engine section. That said, here's the full text of the head bolt check, includes next page with diameter check:
     

    Attached Files:

    #7 Mendel Leisk, Jul 1, 2026
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