this seems like an obvious question if I understood the limitations of torque-to-yield bolts... but I don't.
Frank has hopefully saved me some misery by pointing out that 72 ft lbs (from orig. shop manual) is not enough torque for my head bolts. My question is this:


Is it okay to just do another 8 lbs of torque (to 80 ft lb) in the correct tightening sequence on the bolts I have now?


Or, once they've been "stretched" do I run the risk of popping them? Should I just install a new bolt set? Cost is no biggie, but I wondered if doing that runs the risk of oil/crud falling into the bolt hole -- requiring another cleanout, more work etc. By the weekend, I will most likely only have about 100 miles on the vehicle since buttoning it up if this info makes any difference?


Another request is anyone's opinion on the bolts themselves:


I went with Mitsubishi head gaskets to avoid any problems, but picked up a set of Fel-Pro bolts thinking a bolt was a bolt. Any opinions on this? Should I replace with Mitsu parts as long as I'm tearing into the engine??


As always, thanks for the info and advice!

Bryan

with the ome parts on a head job, its my understanding that retorquing isnt neccessary. i dont think it would be a problem to just torque the bolts already in the heads the extra 8ft.lbs. to the proper torque and call it good. but i would be worried about removing the bolts and replacing them without doing the head gaskets as well. when i did my head job, i measured all my bolts and reused them because they werent stretched.

The head bolts on your motor are not torque to yield so adding a bit more clamping load is not a problem.

TTY bolts typically have a very different tightening procedure where you turn them a number of degrees. Their strength is carefully controlled so that the clamping force is limited by them yielding. Once they have yielded the next yield point is not as predictable so to get a controlled clamping force you need to replace them after each usage.

The 3.0 bolts are the older style; use a torque wrench type. For these bolts its friction and thread pitch that control the clamping force at a given torque. Since the friction is a very large part of the equation (85% ++) and the actual force thatÆs left over is what gets used to provide clamping a small change in friction makes a big difference in clamping force.

ThatÆs why attention to the threads is important.

The Fellpro bolts should be fine.

Kevin

I've been told by MMC mechanics that head bolts on the 3.0L are not TTY bolts and that they routinely re-use them once if the engine didn't badly overheat. I don't know about the FelPro bolts, but they should be fine.

Although I used new head bolts on my rebuild, out of curiosity I measured the old ones against the OE new replacements. No stretch had occurred in the old ones. OE new head bolt length is 4.010" (as measured on the ones I have left over), but IIRC I think I ground mine to 3.998". If you ever try that, you have to grind VERY slowly so you don't lose the temper and the threads have to be wire-wheel brushed (maybe even chased) and cleaned so there's no drag. If you have enough clamping range there's no need to ever grind the bolt length - and preferable that you don't.

In your case, just torque the remaining 8 lb-ft in the same circular pattern as before, beginning with one of the center area bolts and going clockwise around the heads. I think I'd do it in 2 steps - 75 and 80 so you break the initial tension on the first pass and set the final torque on the second pass. Don't wait too long to re-torque or the lubricating value of the oil residue on the threads and under the bolt head may be lacking.

Frank