head bolt torque?

Discussion in '2-Stroke Engines' started by noble b, Jun 7, 2012.

  1. noble b

    noble b Member

    just replaced the head gasket on my grubee and the bolts are 14mm and i was wondering what is the torque inches on that? i went off some of al.fishermans posts and it says 120 to 175 on 8mm i did 150. but sense these are bigger i want to make sure it is right.

  2. GearNut

    GearNut Active Member

    The head studs are either 6mm or 8mm. That is the diameter of the stud, not the wrench size of the nut. Either way, the 150 should do you good. A 14mm nut on a 6mm stud is not common. A 14mm nut is common on am 8mm stud though.
  3. noble b

    noble b Member

    thanks feel really dumb.
  4. Fabian

    Fabian Well-Known Member

    Don't be so hard on yourself noble_b

    It would instantly make you feel better to have seen some of the obvious mistakes i have made along the way with regards to re-engineering a motor bicycle.
  5. Al.Fisherman

    Al.Fisherman Active Member

    In my research, I found that with cast aluminum, the MAXIMUM torque (for 8mm threads) is 215 INCH INCH # (although I never go that high), and with 6mm threads is INCH 75#. In that case the first time I torque cylinder studs I use 120/50, second time I use slightly a little more torque, about 10% more. These are using Metric 8.8 (USS 5) grade hardware, not the cheap Chinese grade 3. To tell the difference in size of the cylinder studs, if the stud is the same as the engine mount studs they are 6mm, if larger they are 8mm. AS mentioned, don't go by the wrench used on the nuts. So with the 150 INCH # that you used, that's just fine, if they are 8mm. With all that said...I have gone as high as 175 INCH # on 8mm, with NO problem.
  6. Chookawatts

    Chookawatts New Member

    I built a 400 chev a few years ago with cast iron block and heads and the torque settings in the chev are 65lbs, 120 seems a bit high to me! oh well I can only crack the head my studs will never break that's for sure! I made them myself and they are the strongest part of the whole bike
  7. BigBlue

    BigBlue Active Member


    that's 120 inch pounds not 120 foot pounds. 120 inch pounds = 10 foot pounds

    AKA: BigBlue
  8. sp454e

    sp454e Member

    sorry my angels have modified wings and they are fast
  9. Chookawatts

    Chookawatts New Member

    Hi BigBlue

    Now you tell me! My head is torqued down to 50ft lbs it must be like a hand grenade at the moment! I wondered with one of the spring washes peeled out like foil, and I had to replace it. Now my question is: if I loosen it off and re torque it to say 10 ft lbs is it going to leak?
  10. Fabian

    Fabian Well-Known Member

    50ft lbs

    I'm surprised the head gasket hasn't been squashed paper thin.
    I'm even more surprised that the head bolts haven't striped out of the cases.
  11. Fabian

    Fabian Well-Known Member

    Time for a new head gasket and correct tension being applied to the cylinder head.
  12. Skyliner70cc

    Skyliner70cc Active Member

    Its its a stock slant head, chances are it is toast due to warping from the overtorque. I use 20 ft-lbs but with aftermarket studs which I JB weld into the block with an aftermarket head.
  13. BigBlue

    BigBlue Active Member

    As Fabian stated I am also surprised you didn't strip the head studs out of the case. Probably should get a new head gasket and check to make sure you didn't crack or warp the head.

    AKA: BigBlue
  14. Chookawatts

    Chookawatts New Member

    So am I fabian, but when one of the washers peeled off, I knew something was wrong so I stopped torquing the head down, I wont be expecting this engine to last long, as that stress must have done something, I have stainless steel studs and a copper head gasket, so all the stress would have been on the head, barrel and casing, I am sure I'll find out quick enough! I re torqued the head to 10 ft lbs and it started and ran the same as before so only time will tell. the head gasket will have to wait as it was a bit of a pain to make with the tools i had, it doesn't appear to be leaking like it was before.
  15. Fabian

    Fabian Well-Known Member

    I can't say that this is true or not, but, the is a chance the dimensional integrity of the barrel might have been affected by the high torque number.
    Check to see if the crankshaft rotates smoothly (with spark plug removed from cylinder head) through a full 360 degrees.
  16. Fabian

    Fabian Well-Known Member

    At the end of the day, these engines are dirt cheap for the surprising reliability they can give; also replacement parts are cheap enough to purchase that it causes only superficial pain to the wallet.