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ARP bolt sanity check

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ARP bolt sanity check

Postby apprentice1 » Thu Oct 25, 2012 3:11 am

I read through old threads on torque/stretching ARP rod bolts... so here's the story. ARP 2000 bolts 7/16" 1.6" long. Torque spec 70 ft lbs, .0062 max stretch. Scat Rods. Using ARP lube, cycling bolts to torque 4 times to burnish...bolts would stretch around .0002-.0005" farther by 4th pull. Bolts were stretching anywhere from .0037-.0047" at 70 ft lbs (Using arp stretch guage). Removed bolts, applied more arp lube to friction points, torqued to 70ft lbs, and then applied enough force to stretch to .006" (didn't actually check necessary torque). The 2 bolts that only stretched .0037" initially took a ridiculous amount of torque to stretch to .006" I split a snap-on 3/8" drive socket and had to get a longer ratchet to get enough leverage. I'm thinking i was well over 100ft lbs to get those two bolts to stretch. Obviousely something wasn't right, so i removed the bolts to see if they had yielded, but they returned to within .0002" of their original length. I cleaned the rod/ cap, and bolts to inspect, but everything looks good and the bolts can be run in smoothly by finger. Re-assembled with fresh application of lube and it pretty much took the same force to stretch them back to .006" the second time. So...do I replace the bolts just because they seem to be too strong, even when they're "behaving properly" besides the excessive torque? Suggestions? I didn't check too see how out of round the rod went from that torque... Thanks guys
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Re: ARP bolt sanity check

Postby apprentice1 » Thu Oct 25, 2012 3:13 am

Where the underside of the bolt head and rod rub the metal was galling a bit...I sanded the underside of the bolt head smooth before stretching to .006" the second time.

The torque wrench was calibrated recently.
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Re: ARP bolt sanity check

Postby barnym17 » Thu Oct 25, 2012 5:00 am

I would check the rods for out of round condition at the proper stretch,if they were tourqed at 70 and sized and you have to pull way past that for proper stretch they may be distorted.
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Re: ARP bolt sanity check

Postby dfree383 » Thu Oct 25, 2012 5:07 am

won't hurt to check your torque wrench calibration from time to time too.
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Re: ARP bolt sanity check

Postby k-star » Thu Oct 25, 2012 6:01 am

I see that all the time, nothing really out of sorts there. Go by the stretch gage and don't worry much about the required torque.

I did some testing in my shop with maybe 8 or 10 different rods/bolt configurations, and the only way to really get the bolts correct is with a stretch gage. There are way to many factors that can change the required torque.


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Re: ARP bolt sanity check

Postby PeterGunn » Thu Oct 25, 2012 6:04 am

I've ran across tough rod bolts before also. Try cycling them a few more times, always adding thread lube every pull (under the head and on the threads)...just be careful because the torque needed to get to the proper stretch can drop quick.
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Re: ARP bolt sanity check

Postby apprentice1 » Thu Oct 25, 2012 9:49 am

Ok thanks for the replies!
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Re: ARP bolt sanity check

Postby Runit » Thu Oct 25, 2012 10:08 am

Years ago when I first dealt with Carrillos and SPS bolts I had difficulty getting consistent bolt stretch. The lube Carrillo supplied at the time would allow much more stretch if you torgued the freshly lubed bolt to the final value in one uninterupted motion. If you stoped at an intermieadate torque and then continued the bolts didn't stretch as much. If I remember correctly, on a 3/8s bolt the difference was as much as.0025". Jack Sparks he did some testing that confirmed my findings. He subsequently changed the wording on the literature that came with the rods. He also changed the bolt lube some time after that. I've never used torque only since then.
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Re: ARP bolt sanity check

Postby fast_crew » Thu Oct 25, 2012 10:21 am

Ran into the same thing last week torquing a set of ARP 625 3/8's bolts in a set of Dyers, Oil at 55lbs was about .003" ARP lube 55lbs, .0035, 60lbs .0038. Contacted Dyers they use CMD #3 EPL., 57lbs achieved .0055 The CMD appears to be a much better EPL.
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Re: ARP bolt sanity check

Postby In-Tech » Thu Oct 25, 2012 10:54 am

CMD rocks. ARP and other bolt manufacturers don't, It makes me worry about stretch anymore :cry:
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Re: ARP bolt sanity check

Postby Milan.. » Thu Oct 25, 2012 10:55 am

Been through that many times , just had a set of 8740 7/16 rod bolts in Eagle rods. Lubed and re-lubed(with ARP lube) , they need #85 to make .006
I feel lots of people torque , then assume stretch will be correct ... Thanks Milan
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Re: ARP bolt sanity check

Postby cnsperf » Thu Oct 25, 2012 7:05 pm

Could someone post a link or a source for the CMD#3 lube please. Thanks in advance.
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Re: ARP bolt sanity check

Postby 540 RAT » Thu Oct 25, 2012 7:34 pm

apprentice1 wrote:I read through old threads on torque/stretching ARP rod bolts... so here's the story. ARP 2000 bolts 7/16" 1.6" long. Torque spec 70 ft lbs, .0062 max stretch. Scat Rods. Using ARP lube, cycling bolts to torque 4 times to burnish...bolts would stretch around .0002-.0005" farther by 4th pull. Bolts were stretching anywhere from .0037-.0047" at 70 ft lbs (Using arp stretch guage). Removed bolts, applied more arp lube to friction points, torqued to 70ft lbs, and then applied enough force to stretch to .006" (didn't actually check necessary torque). The 2 bolts that only stretched .0037" initially took a ridiculous amount of torque to stretch to .006" I split a snap-on 3/8" drive socket and had to get a longer ratchet to get enough leverage. I'm thinking i was well over 100ft lbs to get those two bolts to stretch. Obviousely something wasn't right, so i removed the bolts to see if they had yielded, but they returned to within .0002" of their original length. I cleaned the rod/ cap, and bolts to inspect, but everything looks good and the bolts can be run in smoothly by finger. Re-assembled with fresh application of lube and it pretty much took the same force to stretch them back to .006" the second time. So...do I replace the bolts just because they seem to be too strong, even when they're "behaving properly" besides the excessive torque? Suggestions? I didn't check too see how out of round the rod went from that torque... Thanks guys


As for the your bolts, the fact that they didn't go quite all the way back to their original length, tells you that they've just started to go past their elastic limit and have just slightly started to yeild. Personally, I would not run them, because rod bolts are too critical. You want them to still be in their elastic range.

I ran into your exact same problem with those exact same bolts. The big concern was weakening the threads in the rods, and perhaps even pulling them out during torquing or later while running, as well as exceeding the elastic limits of the bolts. After numerous times cycling them and trying to reach the recommended stretch, I finally talked to ARP Engineering as well as the Rod Manufacturer, to see what they recommended, since they know their products better than anyone else.

Long story short, they ultimately said to torque the bolts to 75 ftlbs, walk away and forget about trying to achieve that last small amount of called for stretch. Rod bolts were installed with only a torque wrench for decades without issue, before anyone ever created bolt stretch gauges. Just sayin'.......
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Re: ARP bolt sanity check

Postby 63bobby » Thu Oct 25, 2012 8:17 pm

Reading this post gets me woried just finished up a 383 sbc build with a scat assembly said on rod box dont excide .0046 strech . So I purchased a arp strech guage . And they only went to 0025-003 at 63 lbs . put the torge quage down and
slowly went to .004 . I kept checking with guage . check all the bolt witha 1/2 snap on wrench and some bolts went to 90 pounds and some 70 . Well I ran the motor and broke it in . 50 miles around town 3 full runs shifting at 6000 rpm . No lose of oil pressure . nothing losen up yet . But I built a jeep 12 years ago ,and the motor had arp bolts and the engine shop said just torque 3 time with lube . Didnt even think about strech . motor is still running . who thought of this head ache!!
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Re: ARP bolt sanity check

Postby needforspeed66gt » Thu Oct 25, 2012 10:04 pm

Par for the course with the ARP hardware in the cheap offshore rods, spec says .0046" stretch, torque at 64ft/lb, but in reality when you measure what it takes you'll be in the 85-90 range to get the stretch on the fastener right....you gotta wonder if the Chinese steel is compressing under the clamp load rather than the bolt stretching, doesn't happen with the high dollar rods.
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