torquing down head bolts on 66cc hlp


Local time
11:36 AM
Jun 22, 2008
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
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?
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.
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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.
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)
I JB weld the bottom of my studs. I have never broken a stud but have had one strip out of the bottom.
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.
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.