Pease Clarify, Head Stud Turque specs etc...

Discussion in '2-Stroke Engines' started by TINKERER, Mar 2, 2009.


    TINKERER Member

    Yes I did a search, and I cannot find a clear answer.

    1. What type torque wrench should be used in/lb or ft/lb?, and what would be the most practical wrench to buy if you wanted to use it for other applications?.
    2. What is the proper techique for torqing the head studs?
    3. What are the torque specs for the common HT engines in in/lb and ft/lb?, if the specs vary based on displacement please list them.
    4. If the head studs should be upgraded what should be used? and what nuts/washers should be used?
    5. It sounds like stripping head studs is very common, I hope it does not happen to me. so maybe this should be a sticky or added to the first time checklist.

  2. bluegoatwoods

    bluegoatwoods Well-Known Member

    I torqued mine to 12 ft/lbs. I think I got that figure from a thread here. Or else it was on my vendor's installation instructions.

    I did it in three steps; first I finger-tightened them. Then I took them down to (about) 6 ft/lbs. (it was probably five) I tightened one, then the one opposite. Then I moved to the next one and it's opposite. I repeated the process to 12 ft/lbs.

    I used a cheap, ratcheting, 3/8 in. drive torque wrench from Harbor Freight that I bought maybe 5 yrs ago. I suppose the biggest worry with these is accuracy. And maybe that really matters when you're dealing with 5 or 12 ft/lbs, as opposed to, say, 85 ft/lbs. But my head seems to be screwed on right. (insert joke can't pass up an opening like this......)

    by the way, the engine in question is a 49cc, happy time. I don't know if the "80" cc needs the same torque, but I'm willing to guess that it's so.
  3. BoltsMissing

    BoltsMissing Active Member

    When you tension the head bolts, be sure to back-off a bit first so it "cracks" undoing, then a slight turn more loose, then tension.

    If it cracks while tensioning, it might snap, yet it might not. It's a 50/50 risk, so best to slacken then tighten.
  4. Mountainman

    Mountainman Active Member

    HF -- accuracy should not be off that much

    it seems that the low price Harbor Freight should work fine
    accuracy should not be off that much -- if any

    for good quality -- Sears Craftsman -- of course
    but -- how often will it really be used ?

    ride the motor bike
  5. Mountainman

    Mountainman Active Member

    Bolt's got me thinking about something here

    Bolt's got me thinking
    with the quality of some of these -- if I may say Bolt's ((bolt's))
    it may be a good idea to loosen the bolt's
    and apply a small amount of oil to threads
    running the nut up and down a few times

    now smooth running nut -- making for a smooth torque down

    ride the motor bike
  6. arceeguy

    arceeguy Active Member

    I use a Harbor Freight 1/4" torque wrench to torque the head nuts, and I replace the acorn nuts with standard 8mm metric nuts w/lockwashers. The 12-15 lb/ft required is on the bottom end of the 3/8" torque wrenches, so I questioned the accuracy and purchased the 1/4" drive unit and a 1/4-3/8" adapter for the socket. I torque the nuts in a crisscross pattern in stages. (8/10/12/15) And I recommend that they be checked every 50 miles or so.

    Before I install any engine, I remove the jug and studs, flush the stud holes with solvent and blow them out with compressed air. Then I apply red loctite and thread the studs until they bottom out. Then I re-install the jug and torque down the head. After a 10 mile "break-in" run, I re-torque and consider the bike ready for sale.
  7. seca40

    seca40 New Member

    In my opinion it may be better not to leave the stud bottomed out in the hole. Dis similar metals will expand different amounts when heated. Leave room for the studs to expand if need be. A quarter turn is standard practice. I torque my head to 10 pounds. So far so good.

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  8. arceeguy

    arceeguy Active Member

    Good point!

    I guess I will back off 1/4 turn from now on.

    The aluminum engine case should expand more than the steel stud, but I'm not sure if that's better or worse than if the stud expands more.

    On an encouraging note though, I have sold many engine kits and haven't had one case of the studs pulling from the crankcase.
  9. Pablo

    Pablo Motored Bikes Sponsor

    1)Low range ft-lbs works fine
    2) As others say criss-cross, sneaking up on the recommended torque.
    3) 10-12 for the 6mm studs. 13-15 for 8mm, 14-16 for the 8mmX1.00.
    4) I say upgrade for $9.95 w/all washers and nuts:
    Head Stud Kits
    5) Mostly happens due to the lousy cap nuts.
  10. MikeJ

    MikeJ Member

    Hi Everyone -

    New guy and new purchaser here. A question about head nut torque, please... I was checking the new 66cc Nantong engine, fresh from factory (unpainted model). The head nuts are 10mm. I used my own moment-arm and weight system as a calibrated torque socket wrench: A rachet handle with light copper pipe extending horizontally outward. I have read that headnut torque should be 12 ft-lbs (8 pounds at 1.5 feet). But I measure the headbolts and I don't even think I am getting 6 ft-lbs of torque resistance. I tightened each headbolt nut about 10 degrees and stopped. I am not getting the resistance I am expecting. I have to wonder if the studs are stretching, the head gasket is compressing, or the crankcase threads are stripping. What has been your experience when tightening down headbolt nuts?

    Thanks for all replies,
  11. Pablo

    Pablo Motored Bikes Sponsor

    Wow - if they are 10mm, that means the thread size is 6mm. Are you still using the acorn nuts?
  12. MikeJ

    MikeJ Member

    Yes, the engine did come with 6 mm studs. I tightened them down in criss-cross sequence. Before I got to 10 ft-lbs, one of the factory-supplied studs snapped clean off, near the top. I removed them all from the engine and threw them into the trash. Tried some hardware store substitutes, grade 8.8; one of them snapped near the base. Pulled them all out; will use elsewhere. Ordered Grade 10 studs from USABikeMotors. Will install them tomorrow. I do NOT expect them to break at 10 ft-lbs. Unless someone can justify why 12 ft-lbs is needed on 6 mm studs, that is where their torque will stay. (Tomorrow is Tuesday. I should be riding by the weekend with new shift kit!)

  13. MikeJ

    MikeJ Member

    By the way, the engine arrived with pass-through nuts that require a 10 mm wrench. I will use those. I throw all acorn nuts away as well and use pass-through nuts.

  14. solitus3989

    solitus3989 Member

    All i had was a weird torque wrench.

    Yes; 12 ft-lbs = 144 inch-lbs.