torquing down head bolts on 66cc hlp

Discussion in '2-Stroke Engines' started by pedalpower, Jul 31, 2008.

  1. pedalpower

    pedalpower Member

    So, I was torquing down the nuts on the stock head studs and had the wrench set on 14 ft/lbs. one of the stock studs just sheared. I replaced them with new allthread (8.8) but I guess the new gaskets are just seating and so it feels like I'm turning the wrench more than the stock bolts or even the new studs will take.

    Any sharing of similar experience with this is appreciated. I'm just afraid of trying to go to recommended 17 ft/lbs and risk stripping the bottom threads and trashing the engine.

    the studs have been securely seating in the bottom threads by locking 2 bolts together and turning into the thread until the bolts themselves started turning (a couple drops of blue loctite were added).

    tanks. jon

  2. NunyaBidness

    NunyaBidness Member

    hey Jon
    don't worry too much if you do strip the threads, they can be fixed fairly easily.
  3. pedalpower

    pedalpower Member

    thanks. i would prefer not to strip anything and I probably won't so I'll probably just do a initial warm up and let it cool and then retorque. I'm glad the first thing i did after getting my engine was go to to get a nice supply of m6 8.8.

    so, if I strip i have to retap to 1/4" or m8 or can I stay with m6 somehow?
  4. iron_monkey

    iron_monkey Guest

    I normally dont tighten the headstuds using alot of force , especially in my kit where the nuts and stud are one peice. I dont want to strip the threads on the block; or worse shear the stud in the block.
    I dont even use a conventional wrench, only a nut turner that only uses the twisting force of your arms to turn the nut - not sure of the exact name of this tool.

    I hope Loctite should be able to keep them from loosening.
    Last edited by a moderator: Aug 2, 2008
  5. pedalpower

    pedalpower Member

    thanks. when I replaced my studs I made them a little longer 475" instead of 4.5". I also installed a washer that is slightly smaller than the stocker-this creates a stepped effect and stops the lock washer from causing the larger washer to "pool" into the space around the stud in the head. It is a much more stable seat and I immediately felt the bolt tighten up and not continue to give as the turning caused the washer to bend.

    I also have enough space to add a second bolt and lock it against the stock bolt and loctite it and make a sharpie mark on the top of the bolt that will let me know if there has been any obvious movement.

    I've been doing most of the work with a 10mm open/closed wrench. I don't know what a nut turner would be unless it is like a screwdriver with a socket on the end of it.
  6. BoltsMissing

    BoltsMissing Active Member

    If you feel compelled to re-torque the head bolts on a brand new first start HT after initial warm-up,( or head gasket re-placement) it might pay to back off the nut first to avoid the "crack" snapping the long head stud.
    If there are quality spring washers in place on top of a quality flat washer under the quality nut, I don't think you need to add another "lock" nut cos heat and expansion tightens it further, but a dab of locktight ought to secure it well enough.
    Just an opinion, worth $0.02 cents ( tax free)
  7. Skyliner70cc

    Skyliner70cc Active Member

    I JB weld the bottom of my studs. I have never broken a stud but have had one strip out of the bottom.
  8. mountain80

    mountain80 Member

    I went with grade 10.8 allthread and used hardened nuts and flat washer with a copper washer against the head like a lot of motorcycles use. Retorqued it once to 16 ft/lb and it has never loosened again.
  9. smitty

    smitty Guest

    I sheared a head stud at the crank case while re-torquing the head bolts on my HT. Three of them did fine and the fourth sheared. I managed to drill it and remove it using an an Allen wrench ground to a square taper on the short end, and hammered into the stud. I bought stainless steel all thread to replace the studs. I decided that the stud sheared because the nut was not lubricated at the factory, and had frozen on the stud. I suggest using an anti seize compound on the threads before assembly.
  10. BoltsMissing

    BoltsMissing Active Member

    Perfect, appears problemo is solved, copper washers. Thanks.
  11. Skyliner70cc

    Skyliner70cc Active Member

    FYI, if you use antiseize on the top thread of the stud that holds the head, you cannot use the normal torque value. You should lower your torque value by about 50% or you risk shearing another stud.
  12. mralaska

    mralaska Member

    I have seen copper washers used when they are needed to help seal but I was not aware of any properties that would give a more reliable bed than steel to seat on unless the bed itself was warped and the washer needed to settle or something, but even steel should bed down under pressure. My flat washers seemed to be sitting flush on the mounts but I did not get a light in there to properly investigate.

    That being said, I have been having touble getting my head bolts to torque and was unable to find copper washers after reading this post so I drilled out some pre-1982 U.S. pennies (95% copper) and fabricated my own washers which may have helped a little but I cannot be sure. I am still wondering if I should order some regular copper washers.

    I replaced my head bolts using 246 loctite with m6x1 8.8 allthread from along with washers and nuts but still I get that sickening 'keeps on turning' feeling when I tighten the head bolts. After replacing the flats with the thick copper washers I made out of the pennies, I finally got the wrench to click at 120 in. lb but further tightening was just too scary. I have seen recomendations range from 90 in lb to 17 ft lb. At this point I am inclined to stick with 120 in lb which is the lowest setting on my wrench, or I might just use my calibrated arm to go to 8 or 9 ft lb next time I have the head off.

    I would be interested in whether other people have had similar problems as mine. When I cinch down the head bolts at all it never seems to seat and feels like I am pulling the threads right out of the crank case. I have considered JB Welding the bolts in also but I do not know how I would ensure getting good coverage or even if I would be able to get the bolt hole clean enough for a proper bond.
  13. mountain80

    mountain80 Member

    16 ftlb is for 8mm studs. 9ftlbs is for 6mm studs, I looked up some torque specs for metric bolts in one of my motorcycle repair manuals.
  14. Skyliner70cc

    Skyliner70cc Active Member

    I JB weld all my studs. Very easy to do. Use brake cleaning spray to clean out the threads on the block and on the stud. Once evaporated mix JB weld and coat the threads on the studs and screw in as normally.

    I don't torque with a torque wrench. I just tighten 'em up as much as I can and loctite the nuts with red loctite. I also use locknuts, lock washers, and a wave washer on my headstuds. I haven't had a loose head in a long while.
    Last edited: Sep 2, 2008
  15. mralaska

    mralaska Member

    Thanks guys, and sorry for hopping into this thread with my questions but it seem relevant even though I have 6m studs and it appears most of the larger engines have 8m studs. I have left the copper pennies in there for now just cuz I think they're cool and I'm lazy but 9 ft lb is only one notch below the minimum setting on my torque wrench so I retorqued to 108 in lb and they clicked into place without any problem.

    I am thinking (hoping) that the sickening feeling I had was not stressing the threads but rather twisting the class 8.8 (grade 5) studs where a class 10.9 (grade 8) stud might have sheared or pulled the threads out. If things work as is I will quit messing with them but it is nice knowing I have a backup plan if the loctite I currently have in there proves inadequate and I do need to replace the studs into a more solid thread base.

    Attached Files:

  16. willie634

    willie634 New Member

    Well i just scrapped my engine.

    I was. Trying to torque the studs in at 15ft pounds so they would stay put when i double bolt top.

    In doing so the crankcase metal bent inwards right against the crankshaft. Now engine will not turn at all.

    Next time i will double bolt the stud around 20 ft pounds befor installing, that way i am using a regular bolt that can only loosen at one place and not two. Also the stud will not bottom out.

    I would like to find m8 1.25 x 100mm hardened bolts instead, but havnt sourced them yet. The double bolt ideal should work the same though.

    I like the copper idea, with lock washer. Although some canadian pennies are not copper all the way through.

  17. crassius

    crassius Well-Known Member

    bummer, I'm a repair shop and have done 100s of motors over the years and not once had a problem torquing to 12# or less - I suspect that anyone needing strange solutions for head leakage is overlooking some other cause for that problem
  18. willie634

    willie634 New Member

    I was experimenting with double nut method.

    I tightened first nut at 13 then second at 12. Except the stud still came loose when opening. So i figurred i would torque stud at 15 so it stays put. But was too much.

    By switching to a bolt instead of nut and stud, there is only one point that can loosen and not two. I think i am over the double nut. But double nut may work well if you can secure stud in place, but i need mine removable for access.

    So my next attemp will be solid bolt (that doesnt bottom out) with copper washer and lock washer at 12'/lbs. Sound good?
  19. butre

    butre Well-Known Member

    you don't torque the studs at all, you torque the nuts. the studs should be hand tight and then backed off a quarter turn.

    if you timesert the case and use stainless studs you can put about 20 foot pounds on the nuts using that method
    willie634 likes this.
  20. crassius

    crassius Well-Known Member

    not sure why the concern over whether studs come out when you try to loosen nuts - one rarely needs to loosen them and it doesn't seem to matter if the stud comes up