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  1. #1
    Cadet
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    Default stripped threads on head bolt model 470 mercruiser

    Hello Guys,

    I have a 1984 3.7 mercruiser. I stripped the threads from block while torqueing the head (new gasket). So I drilled
    and tapped a new heli coil into the block. I had asked a local machinest if I should install 2 sets of the coil into the threaded hole but he said it wasn't needed. I torqued the head down in 3 stages to 130 ft. lbs.(found the info on that on this web site).
    The re-worked threads held and felt just like the rest. Started the engine and warmed it up to operating temp. A few days later I took the valve cover off to re-torque and that same bolt didn't hold. It's at 90
    ft. lbs. and I can turn it just enough to tell its not getting tighter. Will this hold up for a season? If not how can it be
    repaired again. Also is there a way to repair this without removing the head. The stripped bolt is on exaust side and the
    first one toward front of engine. Thanks for your advice.

    Paul

  2. #2
    Commander RogersJetboat454's Avatar
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    Default Re: stripped threads on head bolt model 470 mercruiser

    With out the proper, even clamping force, it's a crap shoot if the gasket will hold. You have an open deck engine, with a head of dissimilar metal working against you too (expansion rates are different).

    As far as repairing it with out pulling the head, I just don't see it happening.
    1976 Rogers Custom Boats 18' "Bonneville" W/ Chevy 454/ Berkeley 12JC

    Care Taker of 1976 Glastron V-184 Crestflight W/ Volvo 170B/280 I.O.
    & 1969 Starcraft W/ 1956 Evinrude 7.5hp Fleetwin.

  3. #3
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    Default Re: stripped threads on head bolt model 470 mercruiser

    How do I get the heli coil threads out and should I use 2 sets of heli coil threads this time?

  4. #4
    Commander RogersJetboat454's Avatar
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    Default Re: stripped threads on head bolt model 470 mercruiser

    Quote Originally Posted by jones,pj View Post
    How do I get the heli coil threads out and should I use 2 sets of heli coil threads this time?
    Point 1;
    If you can get to the tip of the coil, you may be able to pry it up with a pick or very small slotted screw driver. Once you do, grab a hold of the raised section with some needle-nose pliers (vice grip version would work best if you have room for them), and carefully pull the insert out.

    Point 2;
    If the heli-coil your using isn't long enough, get a longer heli-coil. They come in all different lengths.
    1976 Rogers Custom Boats 18' "Bonneville" W/ Chevy 454/ Berkeley 12JC

    Care Taker of 1976 Glastron V-184 Crestflight W/ Volvo 170B/280 I.O.
    & 1969 Starcraft W/ 1956 Evinrude 7.5hp Fleetwin.

  5. #5
    Cadet
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    Default Re: stripped threads on head bolt model 470 mercruiser

    Thank you for the info!

    Paul

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