stretch gauge - how to??

[YTNUKLR]

I never whole-heartedly trust a torque wrench, spec. or not, on rod bolts. There are too many variables, including t-wrench calibration, non-static or static torque, variable friction of the fastener, etc. I double check with two different calibrated (beam & click type) t-wrenches on any fastener that matters at all. But, I use stretch for the rod bolts.

The best (in my opinion, only) way to torque 911 rod bolts is with a stretch gauge. Obviously, OEM rod bolts are junk after you torque them once. ARP bolts are fine to re-use until you measure .001" stretch (untorqued) permanent elongation. That's one gradation line on your dial indicator.

ARP makes a decent stretch gauge, and a micrometer will also work.

Do you have all 12 original bolt lengths, as well as all 12 torqued/stretched bolt lengths? If you don't, I don't see how you could know what amount each bolt stretched. The rod bolts are a really bad place to guess, or get "kind of" correct. I say that with your best interest in mind.

[snowman]

I agree. Consider the cost of an entire engine, vs the cost of a new set of rod bolts, then answer your own question.

Stretch, even on a cheep guage from Tiwan or manchow, is much more accurate than any torque wrench for tightening rod bolts, even Snap-off. Torque is up to 50%off, even with the best wrenches. If your uncomfortable with the stretch guage, then use a micrometer and small incremental turns of he nut. Just remember, that if even one of these bolts, snaps, your engine snaps. Its not hard, I do it all the time, for every engine and if I have trouble, I do it over.

Edited - Z-man.

[armandodiaz]

new update, I loosened and tightened the nuts again (fourth time) and carefully measured the bolts. This time I put a square magnet against the rod cap so I can press my guage against it to keep it straight and square.
When I measured them loose they were all Exactly 2.960
I left them alone for a couple of hours to let the metal settle (just being anal). Then I decided to tighten them in stages. Stage 1: 26lb. Stage 2: 36lb. Stage 3 50lb.
I measured the bolts again and ALL read 2.968.
Remember spec is .011 so now I'm .003 under stretched. Which is better than overstretched. The last readings with the .002 over must have been because the guage was not square.

I'm going to loosen them 1 last time but this time I'm picking up a "real" guage(not made in China) from my brother. He's also taking my torque wrenches to get checked out at his job. They have a device where they are suppose to regularly check their torque wrenches. I'm also going to take the rod caps off clean all the lube off the bolts and apply new lube.

So the new question is when I torque them down to I settle with the .008 stretch or should I try and tighten them more? I'm going to pose this question to their tech support.

[YTNUKLR]

Tighten them to ARP stretch specification, about .011" or .012" (don't have the info sheet w/ me here).

[patkeefe]

Armando:
When you talk to tech support, speak to Mike. He is the man at ARP regarding this stuff. You cannot equate torque values with stretch; too many variables. If you overstretch the bolts, you will effectively turn them into $400+ worth of junk. Best to be on the lower end of stretch.
Pat
Pat

[snowman]

Your will find the torque will drop each time you tighten the bolts, to achieve the same stretch. Again go by the stretch, NEVER the torque. Do some research on the subject and you will find that torque is a lousy method, highly inaccurate, no matter how well the wrench is calibrated. How inaccurate? Up to 50%!!!! Stretch works even if you use peanut butter for lube.