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Torquing ARP headstuds

 
 
 
 
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Old 10-16-2009, 08:40 AM
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Default Torquing ARP headstuds

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 itís 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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Old 10-16-2009, 10:06 AM
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I too have read many threads on torqueing head studs and when I did mine I followed the ARP directions that come with the stud kits.

here is what the direction sheet says that comes with the ARP 12mm stud kit (non 625)

PRELOAD ( TORQUE) RECOMMENDATIONS

Following the manufacturers recommended torque sequence, cycle the head studs three times ( tighten, then loosen) to the torque specification of 125 ft lbs with ARP Moly Assembly Lubricant before tightening the studs a fourth and final time to 125 ft lbs.

Tighten the 8mm bolts to 22 ft lbs with ARP Molly Assembly Lubricant.

The ARP 625's are the same just torqued to 145.
 
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Old 10-16-2009, 12:40 PM
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I just installed a set of ARP studs a couple days ago an like what 94 12valve said that is what the directions said an is about like what i did and it seems to work good so far. When i torqued mine though i started 25 and went in the sequence of torquing the head. Then i went over it again an again until none of the nuts turned an then bumped up to 50, did the same thing, then 75 an then 100. After that i went to 125, loosened them up retorqued them to 125. An again a couple more times, before the final torque i let the truck idle to operating temp. an then let it cool off an did a final torque.
 

Last edited by stillbad; 10-16-2009 at 12:49 PM.
 
 
 
 
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