ARP head stud torque?
 

Hi guys, the time finally came; I have all my parts together, ready to finish the motor, BUT, I don't know what specs I should torque the ARP head stud nuts! Anyone know????
Thanks

Check http://www.arp-bolts.com/pages/tech/images/fasttorq.pdf

Thanks Chris, now how do I find out what size and tensile strength are they???
Thanks!

Hmmm Good question...

Didn't you get an instruction sheet with the studs? my rod bolts came with a small 4x5 sheet of paper with the proper torque values...

Probably going to have to wait untill Mon to call them.

Here's the part I left out earlier... I lost that paper!!! I put it in a safe place so I won't lose it, and I forgot where the safe place is!!
I'll call them Monday. Thanks Chris!

i have a lot of those 'safe' places. are the heads of the bolts marked?

So, here's the scoop; the studs are 10mm with a tensile strength of 220,000 psi. According to the chart, the nuts should be torqued at 53 lb/ft, BUT when I called ARP, I was told it was a good thing I called since the chart should'nt be used for precise torque spec figures, but more for a general guideline. The proper torque for 10mm ARP head stud nuts for our engines is 38 lb/ft.

Did they tell you why you should use the lower torque value? I'm curious. I conjecture the reason is the differential thermal expansion (between room temperature and operating temperature) between the aluminum in the barrels and heads and the steel in the studs adds tension to the studs. Aluminum expands at about twice the rate of steel. Cheers, Jim

I had a bit of a confusing situation when I installed Raceware rod bolts.. I was looking to measure bolt stretch to get accurate tightning.. I called Raceware when the lb.ft. numbers didn't even come close to the stretch.. now he tells that the numbers should be OK for the smaller 3.2 bolts but not the larger 2.7 rod bolts..and to keep going till I get the proper stretch.. which was about 75lb.ft./go figure.. this happened over 40k miles ago

Always go by stretch.

If you can measure it accurately - most people don't have a stretch measurement gauge accurate enough. For RaceWare and ARP, *ALWAYS* follow their specific instructions for torque and installation...

-Wayne

I talked to Raceware once about the bolt stretch vs torque. I was having trouble measuring bolt stretch so I asked him about using the torque angle method instead. He said something to the effect that using the T.A. method was fine and lots of engine builders use it. They just include the bolt stretch in case you want to use that method.
-Chris

the issue in my 2.7, so Raceware said, is that the torque # was OK on the smaller 3.2 rod bolts. and the larger 2.7 rod bolts would not stretch at the given torque numbers.. so he said to tighten till given stretch was achived/whatever

Are you sure you used the right stretch numbers?

It seems awfully weird that the stretch wouldn't be right at their recommended torque... Do you use their assembly lube? Did you torque a couple times to "break in" the threads?

All of these things could result in requireing higher torque numbers...

I also noticed that on my ARP rod bolts the torque number on the sheet was much higher than they recommended for actual porsche installation. My stretch measured less than they recommended, but I was using a caliper,not a stretch guage and just did it for edgamucation.

I had Raceware on the phone as this was happening.. The guy confirmed that this would happen..and said the larger 2.7 rod bolts needed more torque to get the stretch than the smaller 3.2 rod bolts..

this was going on in a shop w/a pro because I didn't have the proper tool.. even though the pro didn't touch anything.. [he didn't want any responsibility].. so, I was consulting w/the pro to confirm I was doing everything correct.. and he was watching everything I was doing like a hawk.. even thou my history has a bunch of Chevy rebuilds in it.. I didn't want to screw this up. and the pro wanted me to have a great rebuild..

That's my story.. not saying it's religion.. only saying what happened to me.. this happened over 40k miles ago.. and after the first 1,500 miles of break-in, the car did a 15k mile cross country and a brutal DE after that.. I was still testing my rebuild.. trying to get it to blow up.. after all that I was relaxed.. so the 2nd cross country, a few months ago, was stress free/whatever.

Stretch is the ONLY way to measure how tight a bolt is. On carillo rods, using 1/4 inch bolts, the 912 engine, the stretch is spec at 0.006 inches. The first time it took 18 foot lbs to get this stretch, the second time it took 16 foot lbs and the third time 14 foot lbs. The threads were being burnished each time, making the torque less. Stretch is the most accurate way as torque will depend on thread condition, lubrication, and whatever. Torque values can vary over 100% for the same tightness, stretch values do not.

No question.. it's hard book education

All of this talk about stretch is good theory, however, in practice you can torque the bolts to the factory specs (factory bolts, not aftermarket bolts), and they will work perfectly fine. I have never heard of a non 3.2/3.3 bolt failing because the bolts failed...

-Wayne

Yes all the talk about stretch is good theory. Stretch is the most accurate way to measure tension. The torque required is derived by the bolt manufacturer, based on material properties, area of the section, the coefficient of fiction between the fasteners, etc.

I was on a job a few years ago where elongation and tension were the only criteria specified for the bolts (bolts were through bolts for cable clamps on a suspension bridge).

The method to tension the bolts involved using hydraulic jacks to apply tension, then running the bolts down hand tight. Then a measurement using a micrometer was taken and compared with the original length of the bolt. If it was out of spec the process was repeated.

torque gives a good approximation of the tension required. steel is actually a "plastic" material. There is a range of tension that a bolt will work in below where it yields. Torque figures are typically conservative.

BTW Ive been building 911 engines for about 20 yrs, I always use a torque wrench.:D

We used to use torque wrenches all the time at Hughes when I built Communications Satellites for the Government. We always used torque wrenches - even flexible extensions!

-Wayne