Snapped Head Bolt?

Discussion in '2-Stroke Engines' started by KiDD, May 4, 2008.

  1. KiDD

    KiDD Member

    I was torquing the head bolts and I heard a loud snap, not a good thing. How do I go about replacing it? I already have m6 threaded rod.

    I'm afraid to take it apart I just got it!
    Last edited: May 4, 2008

  2. BoltsMissing

    BoltsMissing Active Member

    Do you mean you torqued the bolts with a torque wrench, or guessed ?
    If you used a torque wrench, what setting was it set at ?

    can you post some pics ?
  3. KiDD

    KiDD Member

    I was using a small click stop torque wrench set to 10 lbs.

    I'm pretty sure one of them is broken.
  4. BoltsMissing

    BoltsMissing Active Member

    undo the bolt you think is broken. If it's broken then you have a job to do.
    If it's not broken, then loosen and smear some oil or spray some CRC under the bolt between the alloy of the head and re-tension. Do that to all other bolts one by one.
  5. KiDD

    KiDD Member

    Yup, I call that broken!

    The bad news is that it is broken. Very broken.
    The good news is that it didn't sheer at the base, but near the very top.

    I'm a positive person, so at least this happen to me now instead of later, giving me a chance to upgrade to quality parts. I just want my Happy Times!

    Click for large image.
  6. stude13

    stude13 Active Member

    was it in. lbs or ft. lbs
  7. KiDD

    KiDD Member

    Foot Pounds.... is there a difference?
  8. stude13

    stude13 Active Member

    there are 12 in. lbs in a ft. lb----breaking that bolt is an indication of the quality of the metal in the. go to a hardware store and replace with quality bolts. not only will they break but you cant get true torque specs. because those bolts also stretch.
  9. KiDD

    KiDD Member

    I already have a meter of 6m all thread. I'm just dreading taking apart the engine to get the bolts out! Is there anything I should be careful about when I take it apart as to not damage anything?
  10. KiDD

    KiDD Member

    I just took it all apart and cut some new head bolts and replaced them put the cylinder and the head on.

    Should I have used loctite? and should I have put made a new gasket for it?

    I'm scared to torque it again
    Last edited: May 13, 2008
  11. BoltsMissing

    BoltsMissing Active Member

    Opinions vary....,

    Do a test, get a nut and bolt in some piece of wood with a hole and tighten them up till you get a feel of what the tension is. Try wood, plastic and steel tests and purposely break a few by over tensioning using the tension wrench indicator each tme, taking notes of the tension setting.
    Once you done this test and see bolt actually break, you'll probably never strip another bolt.

    If you are going to use the same head gasket and the engine has never been started, my guess is it should be ok, up the tension slightly, you'll know by then how tight not to go to by doing this simple test.

    Tighten in 3 stages, for example if the final tension setting is 25 ft/lbs, then start at 10, 17, 25.

    Try without loctite first, my guess at this is, the bolts tension up further due to heat expansion so I don't think they'll loosen up and fall off unless you have not tightened them enough.
  12. KiDD

    KiDD Member

    OK so either this rod I bought is of low quality, or my torque wrench (new) is poorly calibrated.

    I snapped another bolt....

    My questions are that since these were torqued down real tight, should I replace these gaskets? I just go to auto part store and buy some gasket material and cut out the shape for the bottom gaskets and for the metal one on the head what do I do? I only ran the engine for a couple of minutes when I first built it but was not running right, then I gapped the spark plug and torqued the head bolts and broke it the first time.
  13. BoltsMissing

    BoltsMissing Active Member

    Puts a new twist to your engine, "Snappy Time"

    Unless you get some more expirience in not snapping the bolts, a truck load of new gaskets won't make any differance !

    Try again using the same gaskets unless the bottom gasket is damaged.
    The metal head gasket you may as well change it after to have succesfully torqued bolts without snapping them.
    Sorry dude, that's the hard trail ya gonna have to go through, some have the "feel" some need to find it.
  14. kgray

    kgray New Member

    loctite EVERYTHING. trust me, the vibrations will make it come loose if you dont... If gas hasn't hit the gasket, it should be fine to reuse, too.
  15. KiDD

    KiDD Member

    the gasket was a little wet

    I put the engine back together and it runs again, but I am having trouble getting power at the top end
  16. BoltsMissing

    BoltsMissing Active Member

    Good to hear it's running.

    If the engine is brand new, then top end may not happen till about after 500 miles or so, on average.
    In the mean time order some new gaskets, ride it around and by the time you have done a few miles your new gaskets would have arrived.
    Also, tension the head bolts a fraction at a time when it cools down. But don't over tighten. You only need to re-tension once or twice and keep a check on things thereafter.

    When the new gaskets arrive and you have done those 500 miles, then do the job again and by that time you ought to things blind folded.
    Good work though, you got through a phase and hope you feel those bolts before they snap.

    Did you keep a note of the tension settings, if so what were they if you don't mind posting ?

    All the Best
  17. KiDD

    KiDD Member

    I was afraid to put the torque wrench to it again so I just tightened it till right before I think it would break....

    It won't run with the choke open, and bogs when I give it some gas
  18. BoltsMissing

    BoltsMissing Active Member


    check the gap on the plug, 0.025"

    check carby and exhasut for tightness.
    correct fuel mix ratio.
  19. KiDD

    KiDD Member

    The instructions that came with the kit said to gap it to .4 to .5 mm so I gapped it to .45ish mm is that too much?
  20. stude13

    stude13 Active Member

    it is always best to replace a head gasket that has been tightened.