I have a set of Eagle h-beam rods for an LS.. They have the ARP bolt on them.. What is the recommended stretch for tightning down the bolts?

Im not sure on the size but a 7/16" 12point wrench is what fits them.. Anyone know?

I checked the part number on Eagles site and they said that they were 3/8" ARP 2000 bolts if that helps..

 

The bolts are 5/16 ARP 2000. The socket size is a 12pt 7/16. Torque is 28 ft lbs. Stretch is 0.0048-0.0052" as specified from ARP.

 

From 0.0055 to 0.0059 max.

 

Here is the problem.. If I torque it to 43 foot pounds like eagle says for the bolts, then its .0040 on the stretch gauge.. Stretching it to .0055-.0059 makes the torque over 70 foot pounds.. Which is correct, and/or what am I doing wrong?

 

the stretching method is the most accurate method compare to torque wrench. Torque wrench is only used if you don't have the stretch gauge. Eagle recommend's using the stretch gauge. I have one GSR motor fully built w/ Eagle rods same as yours and I stretch them to: 0.0057 to 0.0059. Hope this help.

 

Torque isn't really as accurate an indicator of how much pre-load you are putting on a fastener assembly as people think unless the fastener is assembled under the exact same conditions that the engineers used when they determined the torque/stretch specification. Rod bolts are usually assembled with a small amount of engine oil or other light oil on the threads. The fact that you have to apply more torque than specified to get the proper stretch tells me either the threads are deformed in the bolt or nut or there is not enough/improper lubrication on the threads. You want to strech (pre-load) a bolt just under it's elastic limit or yield point. The elastic limit is that point at which the bolt will not return to it's original length when the tension is released from it (the nut unscrewed in other words). Just under the elastic limit is the point at which the fastener is most fatigue resistant - especially important for rod bolts which are subjected to cyclical loads which may lead to fatigue failure. Rod bolts see some of the highest loads in the engine, especially at high RPM. You could say they are the most important fasteners in the engine.

In your case, check with ARP to see what they recommend lubricating the threads with. All threads in the engine should be lubricated in one way or another. Visually inspect the threads on the bolts and in the nuts. Install them by hand with a little oil on the threads and make sure you can spin them down all the way without any stiff points along the way. If you find that the threads are deformed do not use a tap or die to cut the threads on the bolt or in the nut, you will seriously weaken it. The threads on the bolt are rolled on, not cut, which compresses the metal and makes it fatigue resistant. It you cut the threads with a tap it leaves patches of uncompressed metal in the areas it cut which are points of stress and are the points where the bolt will fail - if it does. There are special taps which do not cut the threads, they are for chasing threads only. If you can't find or don't feel like buying one, leave the threads alone. Like V-SPEC 1 said, use the stretch guage, if you have it, it is the only proper way to set the fastener pre-load. You should be happy you have one available to you. Most bolts on the engine you can't reach both ends of the bolt to measure stretch. That is why it is important to always make sure threads are clean and lubricated with the fastener manufacturer specified lubricant.

A pretty good book on fasteners is <u>Carroll Smiths Nuts, Bolts, Fasteners and Plumbing Handbook</u> by Carroll Smith. It's invalueable for learning (and as a reference to keep in the garage) about bolts, nuts, rivets, snap-locs, and other fasteners plus plumbing of coolant, brake, oil and other lines and is only $15 from Amazon.

-Scott Tucker