trik396

ARP head stud concerns

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I have installed many studs in mains and heads on gassers in the past. I've read almost every thread here in reguards to torquing head studs down. And it seems every one I read is incorrect, at least to ARP's specs. First this is right off of ARP's site.

1. The friction factor changes from one application to the next. That is, the friction is at its highest value when the fastener is first tightened. Each additional time the fastener is torqued and loosened, this value gets smaller. Eventually the friction levels out and becomes constant for all following repetitions. Therefore, new fasteners should be tightened and loosened through several cycles before applying final torque. The number of times depends on the lubricant. For all situations where ARP lubricants are used, five cycles are required before final torquing.

2. The lubricant used is the main factor in determining friction, and therefore, the torque for a particular installation. Motor oil is a commonly used lubricant because of it’s ready availability. If less friction is desired in order to install the fasteners with less torque, special low friction lubricants are available. With special lubes, the required torque can be reduced as much as 20 to 30 percent. It is important to keep in mind that the reverse is also true. If the torque value has been specified for a particular fastener on the basis of low friction lube, installing the fastener with motor oil will result in insufficient preload; the torque has to be increased to compensate for the extra friction caused by the motor oil

Going to the fastener torque recommendations I find that the correct torque for a 12mm stud is as follows.
Using 30wt motor oil - 122ft./lbs

Using ARP's moly lube - 96ft./lbs

I think if the guys here and elsewhere that are using the 122ft/lb number AND using ARP's moly are really over tightening the fastener to a point of possible weakening the stud.
Can anyone here point me to a study that shows in our Cummins application that the studs should be torqued to 122ft./lbs using the moly lube? This is placing something around 30% more pre-load than ARP recommends for this fastener. I would think they should know the correct strength of their product.
If I am wrong, please do not hesitate to correct me. I will be studding the head soon.

Thanks
Tony
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judge88

not saying your wrong but every truck ive done gets 127 ft lbs with moly lube. 30wt oil on the block side. 4-5 retourques. 80 lbs of boost, 50% methenol,lots of nos. drag racing/sledpulling almost every weekend. never one problem doing it this way.

trik396

I appreciate the info. What concerns me is at those torque values, are you stressing the parts more than neccesary? Also, is this actually weakening the clamping process. In other words, shouldn't/wouldn't it be stronger to keep the specs at what ARP says? Where did the 120+ ft./lb with moly spec come from? Seems like it could've been a mistake because that's the spec for motor oil, but everyone is just running with it. See what I mean?

Obviously it is strong enough, at those high levels of torque, but can it be better at the lower level?

trik396

I just got off the phone with ARP. I talked to a very well informed technician named AL. He said the specs I was refering to were "generic" and do not apply to our Cummins.

The correct torque is 125ft/lbs with moly lube. He strongly recommends to install the studs finger tight only in the block using motor oil or moly. NEVER LOCTITE. Using loctite can totally screw up your torque measurements among other things. He suggests doing one stud at a time from center out. Once all are torqued to max, go back and loosen one at a time and go back to 125ft./lbs. Do this three times and you are done.

I stand corrected and I'm very glad I decided to call ARP directly.

judge88 you are correct and I'll likely use your 127 number just in case my wrench is a little on the light side. Thanks.

judge88

good luck to you with the install. hope it goes smooth.make sure the stud is not bottomed out also. i go 1 full turn back out once its tight before i start to tourque.

trik396

Will do... thanks....

95ram

Didn't Don M test ARP's up to some where around 180+ ft/pd before any distortion occured.

judge88

i believe your correct 95 ram.

trik396

That's interesting. Did he post about this in the past?

wap

So your tellin me that you finger tighten them, put the nuts on and torque em to 125, loosen and retorque 3 times and that is it?

No need to heat cycle then retorque?

trik396

Some guys are going to tell you that you need to retorque after a few heat cycles. According to ARP, once the studs have taken "set" after the third or so re-torque, they will not stretch anymore, so there is no need to do anything else. Would it hurt to retorque after a heat cycle... I don't think so.
Problem is you get so many different answers, that's why I went to the source.
Do some reading on ARP's site... good info.

wap

Well thanks for doing my research for me.

I will do it per ARPs instructions, then later down the road when I do injectors I will likely retorque them. Like you said it cant hurt and it would give me some piece of mind.

This info really helped me out, thanks again for posting it.

Jetpilot

Retorques are necessary when running o-rings to ensure proper seating of the ring. We do exactly what ARP said above when not doing o-rings. Use ARP moly lube torque to 125# and do several retorques.

Doug

kantdrive55

One of our customers followed the generic 95ftlbs from arp and first full 55psi pass, he was redoing the head gasket job. Here we heat cycle them twice and retorque twice to 125ftlbs and have had no problems at all.

lmills

Retorques are somewhat of a pain, but far less time consuming than a headgasket LOL