Proper head torque and crappy metallurgy

Discussion in '2-Stroke Engines' started by gearhead222, Jan 23, 2010.

  1. gearhead222

    gearhead222 Member

    Dear Fellow Bikers-Have about 60 miles on my Grubbee 2 stroke and cleaned and regapped the fouled plug today. Decided to check the head torque, as I had it at 10 foot pounds. Decided to go to 12 and "pop!" goes one of the head studs. I had an extra head gasket and stronger head studs from a reputable vendor, so I replaced all of the studs and head gasket. CAREFULLY torqued to 5 and then 7 foot pounds-at 8 foot pound "POP!" goes a better quality stud. What the %$#@^&$%*(#)@@&$#)@) is wrong with this metallurgy?? One of the replacement head nuts even crapped out on me! In pure disgust, I replaced that stud with one of my original head studs, reused the gasket and torqued the head to 5 foot pounds just for ****s and giggles. Amazingly, she actually works. How long I don't know. What are your people's experiences and recommendations with head torque on these bikes? Do you start out at 8 foot pounds and increase to 10 foot pounds later? I cannot even envision applying the recommended 12 foot pounds on the stock hardware. I heard from one person that if it is not leaking, then to stay with the minimum torque that worked. I consider myself mechanically inclined, and this really ****es me off!:shout::snobby::icon_cry:-Gearhead

  2. Skyliner70cc

    Skyliner70cc Active Member

    I purchase allthread from fastenal cut to size for my replacement headstuds. I then JB weld them into the block and torque the ^&*()& out of them (at least 20 ft-lbs) and loctite the nuts with no problems ever. I set it and forget it :)
  3. gearhead222

    gearhead222 Member

    Is this with a Grubbee 48 cc or larger engine? Have heard of people JB welding the studs into the case and am wondering why-Thanx again!:)
  4. Skyliner70cc

    Skyliner70cc Active Member

    Cuz the case is weak and if you torque down on the head bolts or remove them repeatedly to do engine work, you'll strip the threads on the block. JB welding them also prevents them from rotating out from vibration.
  5. gearhead222

    gearhead222 Member

    Gotcha! Did you order the Fastenal 6.00 x 1.00 mm all thread online?Did you have to remove the jug to JB weld the studs?How much JB weld did you use per stud? Would like to install the new studs with JB Weld by slightly lifting up on the jug, so that I don't need to remove the intake or exhaust connections-is this possible?Lastly, what kind of fasteners did you use on the top end? Just one flat and one lock wasjer per stud? Thanx again!:)-Gearhead
  6. machiasmort

    machiasmort Active Member

    On my HT motor with stripped head bolt (stock from BGF), I used 1/4x20 threaded rod, retapped the hole, and jb welded.
  7. chopperjoe

    chopperjoe New Member


    One thing i learned when building my Harley, is dont buy bolts from Ace hardware even though i used stainless steel bolts, they would not go to torque, not even close. I ended up going to Menards, and found much better quality fasteners. Ace sells the cheapest **** they can buy, I found the same problem with hardware store cold steel bolts, they break off at the head at about 3/4 torque. This is on going, i still find myself going to Ace because their close, and then I kick myself In the *** again. I will never drink again either.

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  8. gearhead222

    gearhead222 Member

    Thanx guys! Will be buying the Fastenal rod + quality locking/flat washers from the local nut and bolt store, plus quality nuts! Will also JB weld these babies!-Gearhead
  9. Pablo

    Pablo Motored Bikes Sponsor

    12 ft-lbs seems very high for stock 6mm......10 maybe...but some broke at 8? wow.
  10. Al.Fisherman

    Al.Fisherman Active Member

    After I built my first bike I had a head gasket blow (stretched stock 8mm stud). This was before I changed studs on my son's bike as he was anxious to ride. Out of the next 4 builds, I wouldn't even mount the engine before changing out all the studs. I purchase from a bolt specialty store much like Fastenal. I drop a drop or two of RED loctite INTO the case hole, (piston separated from case) then thread the stud in (double nut, bottom out and back off a quarter of a turn and let set, no torque). I use 120 to 160 inch pounds to start (10 to 15'#) on 8mm studs and can end up with as much as 204 inch pounds (17'#) down the road if needed, and 60 inch pounds (5 foot pounds) for 6mm studs. Using red locktite, should they be needed removing at some time all studs are easily to reach, heated and removed. NOT one failure as of yet, not one. Do not let the exhaust system be supported by the exhaust studs alone, support the pipe well.
  11. MikeJ

    MikeJ Member

    My experience: I snapped one cheap 6 mm stud from China and stripped the block hole of another stud, both when tightening down to the "recommended" 12 ft-lbs of torque. The block became useless.

    I then drilled and tapped the block for 5/16 x 24 by 4 inch long #8 bolts from Ace Hardware. Tightened all four bolts (with washers) to about 9 ft-lbs of torque. Aluminum expands with heat at twice the rate of steel bolts, so as the engine heats, the sealing pressures on the gaskets actually increase. Did not use Loctite.

    That was almost 1,000 miles ago. Have had no problems with this arrangement. Placed some gasket seal around the base of the cheap sparkplug, as it leaked during compression and combustion. That surprised me; but there is no evidence of leaking anywhere anymore. So now, it is "Keep your hands off of what works!"

  12. gearhead222

    gearhead222 Member

    Dohhh annd double dohhhh!!!!Just discovered that my 6mm studs should not have more than 8 foot pounds of torque! What was I thinking??????Still going to chase the holes and JB weld the new studs in place. Is recommended torque sequence 3, 5 and then 8 foot pounds? Thanx again and Dohhhhh!!!!!!
  13. jimraysr

    jimraysr Member

    Stainless Steel head studs and nuts.

    I thought I would mention that, although 316 or 304 stainless steel is great for many applications, it is not as strong as carbon steel.

    An other thing about stainless steel is it gauls to itself. An anti-sieze lube on the threads will prevent this. I am talking about SS nuts on SS studs. Aluminum also gauls, but I have seen very few aluminum on aluminum threaded applications.

    I haven't had head stud problems on the 2 stroke, but did have stud thread problems with the in frame mount for the Honda. I finally tapped them larger and course threads to give deeper contact between the aluminum blocks and the carbon steel studs. Used locktight so that only the nuts will be used. That way as mentioned above the aluminum thread will not be worn from assembly and dis-assembly.

  14. Skyliner70cc

    Skyliner70cc Active Member

    JB Weld: I clean the block and threads and coat the threads of the replacement studs lightly. Been doing this for a long while.
  15. GearNut

    GearNut Active Member

    Another trick to keep stainless steel from corroding in aluminum blocks ( caused by electrolysis due to dis-similar metals, like in a battery ) is to dip the stud or bolt in milk of magnesia before threading it in. Yes, the blue bottle found at most drug stores. The magnesuim content will act as a sacrificial element, virtually stopping the corrosion process. This must be taken into consideration as the aluminum will be the looser, and over a suprisingly short amount of time, you will have a hole with no threads and a stud or bolt falling out.
  16. gearhead222

    gearhead222 Member

    A buddy of mine recommended cutting 4 longitudinal lines in a 6.00 x 1.00 mm stud and chasing a slightly buggered hole using an evaporating solvent. I understand that all studs should easily hand tighten in the holes and this one stud will not:( I would still like to use JB Weld-should I bottom out the holes with the JB Weld applied in the threads? Was going to torque 2, 4, 6 and then 8 foot pounds on the head. Lastly, I am wondering how to properly support the exhaust pipe, as there's no room for a ring clamp. Would wire suffice?Where should I wrap it? Again, thanx for any help:)-Gearhead
  17. Al.Fisherman

    Al.Fisherman Active Member

    There has to be a way of supporting the exhaust...just has to somehow.

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  18. AussieSteve

    AussieSteve Active Member

    I agree with Ron. I was going to post suggesting a photo of your setup, but got side-tracked. (My shift kit arrived in the post.)

    ... Steve
  19. gearhead222

    gearhead222 Member

    Dear Fellow Members-Don't know if this is a first in the annals of motorized biking, but I CAREFULLY retorqued all of the acorn nuts from 5 to 6 to 7 to 8 foot pounds and took her for a 25 minute cruise, after installing some aluminum strap to support the exhaust. I used Al. Fishermans idea and it works great! If I recheck the head torque, it will be at 5 foot pounds-just don't want to risk breaking more studs! I DID order replacement studs and 2 head gaskets, but will be going with this until I have problems. Any comments or opinions? VERY sloppy of me-too tired and working at night-never again!-Gearhead
  20. Mogyver69

    Mogyver69 New Member

    I thought Id mention the most important issue here is a good quality torque wrench. I ve removed heads several times over the yrs, eather to turn the head on a angeled head that doesnt fit the frame or to look at the piston wash etc... Each time Ive re torqued the heads usally big 8mm 70/80cc engines. Start with hand tightening each cylinder bolt and then using your torque wrench start small 60 inch pounds and then 120 inch pounds.... 1 ft pound equals 12 inch pounds so if you need 10 foot pounds 10 x 12 = 120 inch pounds . I like to use a small 1/4 inch torque wrench that measures very small increments. Its more accurate for smaller bolt torqueing. I've never stripped a bolt in one of these engines.... My torque wrench is a Matco $250 dollar tool then again...