Stretching ARP Rod Bolts. Weak Bolt?!?!?!
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From: Fort Lauderdale, FL
Stretching ARP Rod Bolts. Weak Bolt?!?!?! Wile I was torquing my ARP rod bolts using a stretch gauge. I noticed that most of the bolts were whiten .0002 of an inch of each other in length. + or - a few thousandths. BUT, one bolt was about .0007 shorter than the others, and when torqued to ARP's spec of 55Ftbs. Unlike the others that were under stretched with a 55FtLb setting. The shorter bolt was over torqued by about .0008. I dropped the wrench to 40FtLbs and again it was over stretched. The bolts are new, and were installed by the machine shop. I will be calling ARP and the shop on Monday. Curious if anyone has any info on what may be the issue? I am %99 sure the bolt may be defective and have stopped assembly until I get some definite answers. No room for catastrophic engine failure.
Thanks in advance
Thanks in advance
in our race motors the bolt torque can vary 10 to 15ft lbs in some cases to get the same strech of .007
Like you said most of the bolts are usually within a few thousandths at static length, ive never had one that much shorter.
Like you said most of the bolts are usually within a few thousandths at static length, ive never had one that much shorter.
Last edited by i6overboard; Jan 24, 2012 at 10:27 PM.
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Thank you for the replys. The ARP stretch gauge that I have measures in increments of .0005. The .0001 increments were my guesstimate's judging how far the needle moved in between the .0005 lines. All but 2 of the bolts required the gauge to be adjusted back to zero.
After doing some more reading I found out that the bolts should have been measured before their initial torquing. Knowing that the shop didn't do that or use the stretch method during the reconditioning process. I didn't feel it was necessary for me to bother breaking out my mic to measure them since they have already been stretched. Looking back, I should have.
I am worried that the bolt in question may have been a defect out of the box or the shop over torqued it during the honing of the rods big end. Will that bolt be ok to run? Should I change the rod bolts so I can gather a before and after measurement? Can I change the bolts at home without any significantly pricey tools? Will the big end of the rod need to be re-honed after the new bolts are installed?
Any questions or comments are welcomed. I would like to get this engine spot on. Thanks for the reply's so far.
After doing some more reading I found out that the bolts should have been measured before their initial torquing. Knowing that the shop didn't do that or use the stretch method during the reconditioning process. I didn't feel it was necessary for me to bother breaking out my mic to measure them since they have already been stretched. Looking back, I should have.
I am worried that the bolt in question may have been a defect out of the box or the shop over torqued it during the honing of the rods big end. Will that bolt be ok to run? Should I change the rod bolts so I can gather a before and after measurement? Can I change the bolts at home without any significantly pricey tools? Will the big end of the rod need to be re-honed after the new bolts are installed?
Any questions or comments are welcomed. I would like to get this engine spot on. Thanks for the reply's so far.
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I have also read that the rod bolts should be set to the same clamping force that they were honed at. If the shop, torqued them to 55FtLbs and honed the big end. Which by my findings say 55FtLbs is under stretched. And I take them to their correct stretch limit. Will the big end now be out of round enough to cause a problem?
ok now im really confused. im pretty sure your thinking about the wrong decimal place... your talking about stretching the bolts alittle less than a tenth of what arp recommends for most of their bolts at 55 ftlbs of torque. http://arp-bolts.com/pages/technical_torque_us.shtml if you can precisely measure a tenth of a thousandth repeatedly with a mechanically and human ran measuring device then i commend you, and the 2 years i spent using a cnc machine that barely did that was a waste lol! not trying to be a *** but if your lookin for help and i just want to make sure the numbers are right... also i think that your not looking for the same total length after stretch between all of the bolts. your lookin for each bolt measured before stretch and after stretch and looking for that .0050 - .0055 added length after stretch (or whatever your specs are) but if you gain the .0050 by torquing the bolt 10 ftlbs thats when you have a problem id say. someone correct me if im wrong tho, im also building my bottom end with arp bolts too so if im wrong i need to know...
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From: Fort Lauderdale, FL
ok now im really confused. im pretty sure your thinking about the wrong decimal place... your talking about stretching the bolts alittle less than a tenth of what arp recommends for most of their bolts at 55 ftlbs of torque. http://arp-bolts.com/pages/technical_torque_us.shtml if you can precisely measure a tenth of a thousandth repeatedly with a mechanically and human ran measuring device then i commend you, and the 2 years i spent using a cnc machine that barely did that was a waste lol! not trying to be a *** but if your lookin for help and i just want to make sure the numbers are right... also i think that your not looking for the same total length after stretch between all of the bolts. your lookin for each bolt measured before stretch and after stretch and looking for that .0050 - .0055 added length after stretch (or whatever your specs are) but if you gain the .0050 by torquing the bolt 10 ftlbs thats when you have a problem id say. someone correct me if im wrong tho, im also building my bottom end with arp bolts too so if im wrong i need to know...
I am pretty sure my numbers are right. I stretched them all to .0055. The numbers I am posting above are variations between the bolts. Not the actual number I stretched the bolts too.
I am using ARP 100-9942 Stretch gauge. http://www.summitracing.com/parts/ARP-100-9942/ It measures in increments of .0005. Works pretty well IMO. Numbers are spot on each time around. First time I have ever used the tool.
I did the same procedure you described except I made sure to wipe off each end of the gauge and bolt before measuring. ARP's recommendation of stretch is for my rod bolt kit is .0055-.0060"
I also didn't torque the bolts to 10FtLbs. I change the setting on the torque wrench to 40 FtLbs from 55FtLbs. (15FtLbs ess than ARP's spec) and the bolt in question was still stretched too far. Which leads me to believe its a weak bolt.
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I was with BlownEarDrums when we were tightening the rod bolts. Just to clarify, 89gmcs, we measured the stretch of each individual bolt (we zero'ed the gauge with every new rod bolt).
When we torqued the rod bolts to 55 ft. lbs., each bolt (minus the one bolt in question) was within .0005, according to the ARP stretch gauge - which tells me that the measurements appeared to be correct, since we were in the ballpark of the stretch figure given by ARP after we torqued it to the specified ARP number.
The questionable bolt simply would overstretch, even when we turned down the torque rating on the torque wrench. We made sure to let the bolt rest and tapped it with a rubber mallet to help it settle between each measurement.
All the other bolts were perfectly fine and we were able to stretch them to the specified .0055 from the ARP spec sheet.
Another point of clarification - each shorter line on the stretch gauge measures .0005, while the larger line in between measures .0010, correct? The picture posted by Blown from Summit should allow you to see those lines. If thats the case, then we measured correctly.
Thanks for the input thus far - both of us are new to this, but are fairly competent when it comes to things dealing with mechanical assembly.
When we torqued the rod bolts to 55 ft. lbs., each bolt (minus the one bolt in question) was within .0005, according to the ARP stretch gauge - which tells me that the measurements appeared to be correct, since we were in the ballpark of the stretch figure given by ARP after we torqued it to the specified ARP number.
The questionable bolt simply would overstretch, even when we turned down the torque rating on the torque wrench. We made sure to let the bolt rest and tapped it with a rubber mallet to help it settle between each measurement.
All the other bolts were perfectly fine and we were able to stretch them to the specified .0055 from the ARP spec sheet.
Another point of clarification - each shorter line on the stretch gauge measures .0005, while the larger line in between measures .0010, correct? The picture posted by Blown from Summit should allow you to see those lines. If thats the case, then we measured correctly.
Thanks for the input thus far - both of us are new to this, but are fairly competent when it comes to things dealing with mechanical assembly.
Last edited by BadBlackZee; Dec 27, 2011 at 09:32 AM. Reason: sp
ok this sounds alot better. i thought you stretched them a total of .0007 but it was over stretched by that, and also 15 ftlbs low of the 55 ftlbs torque. id worry that the bolt is weak. dont take my word for it solely tho. anything from arp when you called? if ya havent called them yet might aswell give it a shot maybe they will send ya a new bolt rather than having to buy a whole set?
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Just got off the phone with ARP and my machine shop. ARP says DO NOT run that problem bolt. Press it out and install 2 new bolts and nuts onto the problem rod. Machine shop says I'm crazy for using the stretch method and I must have tightened it too far. They only use torque wrenches, even in their 4000hp race car. I have no clue anymore. I'll be ordering new parts by this weekend.
Funny thing is, if I haven't torqued hundreds of bolts before I wouldn't have felt/noticed the torque wrench act up on the problem bolt. And if I hadn't used the stretch gauge I would have not seen just how bad this new bolt is. Pretty wild I caught a potentially catastrophic engine failure before it had a chance to rear its ugly head. If I were to let the shop build the bottom end they most likely not have caught the issue.
Moral of the story. Trust NO ONE. Do everything yourself!
Funny thing is, if I haven't torqued hundreds of bolts before I wouldn't have felt/noticed the torque wrench act up on the problem bolt. And if I hadn't used the stretch gauge I would have not seen just how bad this new bolt is. Pretty wild I caught a potentially catastrophic engine failure before it had a chance to rear its ugly head. If I were to let the shop build the bottom end they most likely not have caught the issue.
Moral of the story. Trust NO ONE. Do everything yourself!
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From: Katy, TX
no kidding! In my industry we are now being required to use precision bolt stretch techniques to achieve a required preload on our products. For most things, you can get away with using a torque wrench only, but measuring stretch is WAY more accurate for knowing your preload in the fastener.
ordering... Just got off the phone with ARP and my machine shop. ARP says DO NOT run that problem bolt. Press it out and install 2 new bolts and nuts onto the problem rod. Machine shop says I'm crazy for using the stretch method and I must have tightened it too far. They only use torque wrenches, even in their 4000hp race car. I have no clue anymore. I'll be ordering new parts by this weekend.
Funny thing is, if I haven't torqued hundreds of bolts before I wouldn't have felt/noticed the torque wrench act up on the problem bolt. And if I hadn't used the stretch gauge I would have not seen just how bad this new bolt is. Pretty wild I caught a potentially catastrophic engine failure before it had a chance to rear its ugly head. If I were to let the shop build the bottom end they most likely not have caught the issue.
Moral of the story. Trust NO ONE. Do everything yourself!
Funny thing is, if I haven't torqued hundreds of bolts before I wouldn't have felt/noticed the torque wrench act up on the problem bolt. And if I hadn't used the stretch gauge I would have not seen just how bad this new bolt is. Pretty wild I caught a potentially catastrophic engine failure before it had a chance to rear its ugly head. If I were to let the shop build the bottom end they most likely not have caught the issue.
Moral of the story. Trust NO ONE. Do everything yourself!
