I bottomed seated the rocker shaft by alternately tightening bolts so it was all the way at the bottom. When I torqued the first bolt there was resistance, but it would not stop spinning. It now looks like I stripped the threads in the head. Why did this happen? I cleaned the bolt holes with compressed air and lightly oiled the bolts. This was the used head from ebay so maybe it was already stripped. Does anyone know the bolt thread size? From what I can find, it may be 3/8. Im going to get a helicoil/thread fix insert. This will work, right?

 

Something is really wrong with my head. Note that this is a used one I ordered off of ebay. The rocker shaft went in fine on the other head.

The two middle rocker shaft holes in the head had to be heli-coiled. When I torqued one of the bolts with the helicoil in, the new tapped threads in the head that the coil inserts into got stripped. I can insert a another coil further down, but I'm afraid the same thing will happen again. How critical is the torque on the rocker arms? I might just torque it to 20 foot pounds with some loctite. Maybe I can put a stud in?

I don't think there is anything wrong with the torque wrench. I used two different ones and both stripped the threads. Plus the torque wrench didnt strip the holes in the other thread.

I'm fairly certain I did the drill, tap and helicoil process correctly because I did a practice run on my bad head and it tightened fine. I also tried tightening as much as I could and snapped the bolt instead of breaking the helicoil.

I noticed the holes for the head bolts on this head were slightly ovular. Maybe it overheated really bad and the aluminum is soft?

 

Toss the head it is shot, some one screwed it up bad.