Pulled rocker assemb stud

[Paul914]

I've got a 74 2.0 that yanked a stud (rocker assembly) out of the head the other day .. it left a pretty good sized hole on the one that was pulled out (intake side #3), and little bit of a wobble on the other stud (outer/ex #3 cyl). I pulled the engine and brought the head to the machine shop to be cleaned up, and have some heli-coils put in the stripped out holes (and valve job while I'm at it). The thing is, I'm not real sure what caused it, and I hate to go through this whole process again in a few weeks/months. The only thing I can think of is that I did't torque the 11mm nuts properly when I last had the assembly off (I must confess, I never use a torque wrench for those things - just go by feel). That was probably a few months back when I change p/r tube seals. Other than that, can anyone think of any possible causes for such a thing?? I've always gone "by feel" (tighten down pretty good w/6" ratchet) on those nuts/studs in the past (on several other cars) and never had any probs - any insight would be apprec .. thanks!

-Paul