Quote:
Originally Posted by icey756
To me i would rather have it over tight then not tight enough.
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And that is where you've gone grievously wrong. Trust me, 99.999% of the time, the engineers who wrote the book (and in some cases helped design the parts/engine/car/whatever) know a LOT more than you.
Heads warp or crack from this kind of mentality... So do rims and brake components; Fuel systems develop cracks, leak and start fires. I don't care if you strip a bolt that's holding in your stereo, but if you're putting 50lbs on a caliper glide bolt which is spec'd for 27 just because you think it's a good idea then you're asking for a fool's end.... I REALLY hope you took greater care when reinstalling your fuel components and lines.
I asked about the lube because different types of lube perform differently. Torquing head bolts to 90ft lbs when using regular 30 weight oil is close to torquing to only 75ft lbs using moly (because moly is a much more efficient lubricant). The torque isn't really the pressure you're aiming for, what you're aiming for is the axial load or clamping force (radial stresses are another concern). Torque offers a simpler way of getting a fastener to within a desired load range. As long the factors involved are as consistent as possible the load on each fastener is more likely to be uniform with those neighboring it and thus less likely to cause undo and uneven stress. One of the biggest factors is friction: threads, cap and washers and lubricants used. Some fasteners actually are hollow so you can measure just how much it has stretched as it is tightened and calculate the clamping force that's been reached... Naturally there are other requirements which render them an impractical solution for your average job. There is a crazy amount of physics behind things as simple as a bolt; I can't say I really understand all of it myself.
Just so you and anyone else reading understands how big of a difference this really is; If assembled dry at 90ft lbs you've got about 11500 lbs of force on each bolt (this doesn't even include the radial stresses). It's supposed to have only around 9500 lbs.
Allowing for variances in each fastener, the threads and other point of friction these numbers will vary a bit from one bolt to the next and with the molybdenum lubricant it's significantly higher. So does 2000 POUNDS of pressure past the bolts rated ability still make you feel better? You couldn't get me to jump out of a plane with a parachute that's rated for even one ounce less than I weight...
Chasing threads (with a thread chase sometimes called a "cleaning chase") is when you use a thread chase to redefine/restore the threads; It's not just about cleaning but it does that too. Lacking a chase you may use a tap but it's not the best as it always removes additional material and can easily ruin good threads and weaken the overall assembly if not started with care. Think of a thread chase as a gentle and slightly rounded tap.
At this point I would probably take more of a "fuck it" attitude... It's not a customer's car, right? If the head hasn't been retorqued yet I might go ahead and back off each fastener 1/4 turn and then one more 1/4 turn. From there I'd measure each with a beam torque wrench, in order, until the tightest one was identified. Torque the others (again in order) until they all meet that one and then give it one more pass and tighten each just 4 or 5 ft lbs to try to ensure uniformity. Run it for a few heat cycles (drive it for a week) and torque a final time to make sure they're all even (back them 1/8 turn or so and then torque back to whatever level you settled on). If you've already re-torqued the bolts and put several hundred miles on it I wouldn't really try much beyond backing them off 1/4 turn (if even that).
Did you have the block resurfaced? If not did you measure it and make sure it is straight?