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Brando
 
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Overtorqued rod bolt

What if I overtorqued two rod bolts? Rod turns fine bit I worry the bolt will break now. It's pretty bad too, like probably 40lb feet.
Old 10-27-2010, 08:37 AM
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Brando
 
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Maybe even more now that I think about it. I should probably replace Hugh?
Old 10-27-2010, 08:38 AM
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Throw those away and replace them with new ones.
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Old 10-27-2010, 08:54 AM
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Thanks, done.
Old 10-27-2010, 08:55 AM
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If the bolts are over torqued would you need to replace the bearing when the rod bolt and nut is replaced?
Old 10-31-2010, 09:22 AM
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Quote:
Originally Posted by Florida 911 View Post
If the bolts are over torqued would you need to replace the bearing when the rod bolt and nut is replaced?
no
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Old 11-04-2010, 04:14 PM
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The safest thing to do is to buy a new set. However, if that is a bit inconvenient, and you think it might be worth further investigation, the bolt manufacturer will know what material your bolts are made of and can tell you if you exceeded the Yield Strength, but you have to know how much you torqued them to. And it sounds like you might not??

Most bolting applications specify a bolt loading of 60% of yield. Rod bolts might be a bit higher. The main thing you want to know is if you exceeded 100% yield. If you did or you are not sure, then get a new set. How did the problem happen?

Also, just a tip, the most accurate and consistent way to determine the loading on the bolt is to measure elongation. I don't know if it's possible with your application, though.
Old 11-05-2010, 06:20 AM
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Quote:
Originally Posted by AlfonsoR View Post
The safest thing to do is to buy a new set. However, if that is a bit inconvenient, and you think it might be worth further investigation, the bolt manufacturer will know what material your bolts are made of and can tell you if you exceeded the Yield Strength, but you have to know how much you torqued them to. And it sounds like you might not??

Most bolting applications specify a bolt loading of 60% of yield. Rod bolts might be a bit higher. The main thing you want to know is if you exceeded 100% yield. If you did or you are not sure, then get a new set. How did the problem happen?

Also, just a tip, the most accurate and consistent way to determine the loading on the bolt is to measure elongation. I don't know if it's possible with your application, though.
Porsche Kamax rod bolts are torque-to-yield bolts so you would exceed the yield point even with the factory prescribed torque.
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Old 11-05-2010, 07:11 AM
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The resaon it happened was due to unfamilierity with the wrench..or any torque wrench for that matter as it's been some time since rebuilding or using one. So....
Anyway, I bought a new couple bolts.
Old 11-05-2010, 07:50 AM
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Porsche Kamax rod bolts are torque-to-yield bolts so you would exceed the yield point even with the factory prescribed torque.
That might be what they tell you, but I doubt that it's true. If you exceed the Yield strength of the bolt, it will fail fairly quickly. Also keep in mind that the loading you put on the bolt by torqueing it is a purely static condition. The bolt still has to have sufficient strength to with stand all the dynamic loading conditions. At 6000+ RPM, you have a lot of loading going on, don't you think?

I'll qualify my statement too in that, I'm not an expert engine builder, but I do know a little bit about materials and bolting.

From a bolt supplier's perspective, it serves my business to tell people that the bolts are one time use because: 1) I get to sell more bolts and 2) less liability. I'm being a bit cynical there. The truth is, calculating fatigue loads and cycles is difficult enough in a controlled environment. In an a real world application where the supplier has no idea if the engine has been over-reved or had a miss-fire at high RPM, it really only makes sense to replace the rod bolts. There is no convenient and practical way to determine the remaining life of a bolt, with respect to it's physical properties, after it's been used and subjected to static and dynamic loading conditions. The customer has to spend a few more dollars to insure the cost of the rebuild, but it's money well spent for both sides.
Old 11-05-2010, 08:20 AM
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Quote:
Originally Posted by AlfonsoR View Post
That might be what they tell you, but I doubt that it's true. If you exceed the Yield strength of the bolt, it will fail fairly quickly. Also keep in mind that the loading you put on the bolt by torqueing it is a purely static condition. The bolt still has to have sufficient strength to with stand all the dynamic loading conditions. At 6000+ RPM, you have a lot of loading going on, don't you think?

I'll qualify my statement too in that, I'm not an expert engine builder, but I do know a little bit about materials and bolting.

From a bolt supplier's perspective, it serves my business to tell people that the bolts are one time use because: 1) I get to sell more bolts and 2) less liability. I'm being a bit cynical there. The truth is, calculating fatigue loads and cycles is difficult enough in a controlled environment. In an a real world application where the supplier has no idea if the engine has been over-reved or had a miss-fire at high RPM, it really only makes sense to replace the rod bolts. There is no convenient and practical way to determine the remaining life of a bolt, with respect to it's physical properties, after it's been used and subjected to static and dynamic loading conditions. The customer has to spend a few more dollars to insure the cost of the rebuild, but it's money well spent for both sides.
I'm not an expert engine builder either, but we do have the benefit of the KAMAX drawing of the rod bolt and the factory's admonition that the bolts may only be used once. As Jim Sims explains elsewhere: Another Rod bolt question-why new The shape of the stress/strain curve of the factory bolts is such that you DO stretch them beyond the point of plastic deformation, then you know you have achieved the correct clamping load that will prevent the fastener from loosening.

There is a convenient and practical way to determine whether the fastener has been stretched beyond the yield point: measure it. Some race engine builders keep a log of each of the twelve rod bolts, and they know the precise length prior to installation, and the neck diameter of the bolt. It's easy to measure with a micrometer. If the bolt is loaded beyond the failure point you can expect permanent elongation and necking down, at which point the bolt is junk and discarded. ARP says this albeit with different words on their website and in their product literature-- ARP-bolts.com | ARP - World-leading Fastener Technology

I guess you may be talking about the ULTIMATE yield point where the damn thing fails entirely. . .
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Old 11-09-2010, 05:36 PM
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