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I hinted before about how i had 2 sets of fresh rods at the machine shop to have them modified for floating pins. They also trued up the big end and surfaced it. After that i took them back to check how the rod bolts sized up in them. They installed both the 134-6006 8740 and the 234-6301 PRO2000
The 8740 need 40lbs the PRO2000 take 45lbs per ARP.
They both distorted the rod end over .001. So in reality using .002 over rod bearings when installing ARP rod bolts and having them honed is the proper way to do it.
I will be trying it the cheap way also and checking with a std bearing before i have all of them resized to visually show the difference vs me just telling you. I dont have a dial bore gauge so ill be using plastigauge. Some of you may groan and say get the right tools, but i have quite a few projects going on and would rather leave the rest of the work up to the machine shop. I did have them touch up one rod so ill use the plastigauge on both....and on both sides of the bearing.
Not to get off topic, but at what point would someone need to consider switching to ARP bolts with factory 4th gen rods? I plan on spinning my motor passed 7000
When you say "fresh" rods, do you mean new? New and old rods will likely distort slightly different.
Originally Posted by Ls7colorado
Not to get off topic, but at what point would someone need to consider switching to ARP bolts with factory 4th gen rods? I plan on spinning my motor passed 7000
I would like to see what would happen if the bolts were torqued to LESS than what ARP recommends. i.e. what if they were torqued to 30 or 35? Would you get less distortion with the added benefit of a stronger bolt.
I would like to see what would happen if the bolts were torqued to LESS than what ARP recommends. i.e. what if they were torqued to 30 or 35? Would you get less distortion with the added benefit of a stronger bolt.
What would be the benefit of a stronger bolt without the additional clamp load?
What would be the benefit of a stronger bolt without the additional clamp load?
My understanding was that most rod bolt failures were not related to clamp load directly but related to bolt distortion/stretching at high RPM. This would obviously mess with the clamp load, but it is a result, not the root cause.
What would be the benefit of a stronger bolt without the additional clamp load?
If they were direct replacement bolts meant to be torqued to the same exact torque spec but were guaranteed to stretch less and be nearly unbreakable, wouldn't you still buy them?
People don't typically upgrade rod bolts because they want to tighten them more. They're afraid of stretch or breakage.
They were both rods from used engines that i had machined. So the surfaces were true and round. Then we put the arp bolts in. As expected the PRO2000s did distort a little more in some places. Actual meaurrments are hard to get, but you can tell a difference in the rod hone machine when it hits a "high spot"
Torquing a bolt before its designed clamp load and/or stretch is a very very bad idea. Torquing the bolt is literally what mates the 2 surfaces together and "springs" the bolt inside the hole to hold them together. Using less force would equal spun bearings or any situation of the like.
JUST torquing them is actually the lazy way to do it and provides less actual stretch and load than whay they are designed for. Tightening them in sequence to proper stretch is the best way. You will find that, on nee bolts anyway, torquing to stretch will require more load than what is actually recommended. There are quite a few articles on it.
Normally when you do it you want to "pre-stretch" the bolt in 3 passes. The last pass should give you the desired length.
Everyone doesnt have access to a bolt stretch gauge. The recommended torque gets you in a good range, or if you've measured a few before you can basically get an automatic feel for it.
Doing any less for the sake of saving distortion is completely the wrong way to do it. The bearings are normally the same price, so if you cannot budget the money or time for proper work then its your call whether you want to risk it or not.
At the VERY least id recommend torquing them down then running a stone hone in them to at least help run down any high spots etc. It would definitely help plus any rod would work better with a machined surface vs just putting em back with caked on oil and carbon on them.
There are always what ifs and anecdotes about "well i did it this way and it worked" but everyone wanted to know, so i took the time and found out.
NOTICE THIS SAYS GEN3 RODS. I do not know about a set of gen4 rods, yet. I will try that one in a few months. Also i did not torque the bolts down to the proper stretch. That will happen before the final machining today as that is the proper way. After the bolt has stretched once, it will usually stay sprung in a longer length the next time for installation but dont expect one torque sequence and done either.
Always use some sort of lube under the head of the bolt to get the proper measurements. Not engine oil. Either the arp ultra torque or some other. Again there is an article about that also. Engine oil is better than just direct metal to metal contact, but an engine assy lube etc would be much better.
If you're keeping count, the new rod bolts will have been used at least twice when you go to install them in your engine so take note of that.
My understanding was that most rod bolt failures were not related to clamp load directly but related to bolt distortion/stretching at high RPM. This would obviously mess with the clamp load, but it is a result, not the root cause.
After the bolt is torqued, it will only stretch further if the load trying to pull the rod apart is greater than the clamp load of the bolts trying to hold the rod together. Other than a few exceptions, the only reason a bolt would need to be upgraded is to increase the clamp load through either a higher yield material or a larger size. Once the rod bolt starts to stretch it will either fail due to fatigue, or when the big end distorts so badly that the bearings actually spin in the bore.
Originally Posted by JoeNova
If they were direct replacement bolts meant to be torqued to the same exact torque spec but were guaranteed to stretch less and be nearly unbreakable, wouldn't you still buy them?
People don't typically upgrade rod bolts because they want to tighten them more. They're afraid of stretch or breakage.
If it does not increase the clamp load, then no, I would not see any advantage and probably wouldn’t buy them. If people are buying rod bolts to avoid stretch and breakage, but not increase clamp load, I don’t think those people know how bolts work.
After the bolt is torqued, it will only stretch further if the load trying to pull the rod apart is greater than the clamp load of the bolts trying to hold the rod together. Other than a few exceptions, the only reason a bolt would need to be upgraded is to increase the clamp load through either a higher yield material or a larger size. Once the rod bolt starts to stretch it will either fail due to fatigue, or when the big end distorts so badly that the bearings actually spin in the bore.
If it does not increase the clamp load, then no, I would not see any advantage and probably wouldn’t buy them. If people are buying rod bolts to avoid stretch and breakage, but not increase clamp load, I don’t think those people know how bolts work.
Your 2 paragraphs seem to contradict each other. In the first you talk about the rod bolt stretching due to fatigue. in the 2nd you talk about it being useless to buy rod bolts to avoid stretch and breakage. When a motor is over rev'd does that not add additional force on the bolt holding everything together? Now you replace that bolt with one that has a higher yield strength. Will that not increase the amount of force, i.e. RPM, that the motor can handle?
I'm thinking some people misunderstand how all this works. its not about a "clamp load" that gives you more strength. Let me explain. You install an arp bolt, which is stronger. When you torque it, your not trying to achieve a clamp load per se, you're stretching the bolt. The stretch of the bolt is what keeps it tight and in place. A stronger arp bolt requires more tq to stretch it to the proper length and in doing that, you put more force on the rod causing it to distort out of round because originally it was sized with a weaker bolt with less clamping force. Thats why a arp rod bolt is rumored to cause failures and spun bearings. If you only tq it to factory spec then its not stretched far enough to keep it from loosening......but I've always wondered what would happen if you used loctite......but i'm not gonna chance it!
Not to get off topic, but at what point would someone need to consider switching to ARP bolts with factory 4th gen rods? I plan on spinning my motor passed 7000
FWIW i spin mine 7000 every time i get on it. Stock rods and bolts, not sure if have 3rd or 4th gen rods however. Motor has never been apart. If you have the engine apart, go ahead and put bolts in and have the rods honed. extra insurance. if your not going to have them honed, dont put the bolts in.
Your 2 paragraphs seem to contradict each other. In the first you talk about the rod bolt stretching due to fatigue. in the 2nd you talk about it being useless to buy rod bolts to avoid stretch and breakage. When a motor is over rev'd does that not add additional force on the bolt holding everything together? Now you replace that bolt with one that has a higher yield strength. Will that not increase the amount of force, i.e. RPM, that the motor can handle?
In the first paragraph, I was saying that the stretching causes fatigue, not the other way around.
In the second, I was saying that you don't get the rod bolts to keep from stretching without getting the higher clamp load. The higher clamp load is what keeps a bolt from stretching in the first place.
The higher RPM creates higher loads on the rod bolts trying to pull the rod apart, and it increase with RPM at an exponential rate. Replacing a bolt with a higher yield strength material will allow you to torque the bolt to a higher clamp load. A higher yield material with the same clamp load might help the bolt from stretching a little less, but it's still stretching. Like a paperclip being bent back and forth, it's just a matter of cycles before a bolt breaks.
In the first paragraph, I was saying that the stretching causes fatigue, not the other way around.
In the second, I was saying that you don't get the rod bolts to keep from stretching without getting the higher clamp load. The higher clamp load is what keeps a bolt from stretching in the first place.
The higher RPM creates higher loads on the rod bolts trying to pull the rod apart, and it increase with RPM at an exponential rate. Replacing a bolt with a higher yield strength material will allow you to torque the bolt to a higher clamp load. A higher yield material with the same clamp load might help the bolt from stretching a little less, but it's still stretching. Like a paperclip being bent back and forth, it's just a matter of cycles before a bolt breaks.
This makes my head hurt lol. I'm going to have to noodle it awhile. You replace a bolt with a MUCH stronger bolt but don't torque it harder and the bolt will still stretch almost as much as the original bolt???? Must....compute.....
The clamping force of a bolt is directly proportional to the elastic stretching of the bolt that occurs during tightening -Hooke's Law of Physics. This stretching is relieved following loosening, as long as torque was not applied past the proof load, and which point plastic deformation begins to occur.
Gen 3 rods, stay around 7k. I set my limiter at 6900
Gen 4, does anyone know? Not sure if anyone revs that high. Texas speed did a ton of pulls over 8k with their LS3 camaro they were out setting records in recently. They did end up popping the bottom end due to rpm though, but it was a money shift that took it out.
As for resizing, some people get lucky without doing it, some don't. Been many threads on it. Sometimes russian roulette works out just fine....
They dont like 8k at all. And that was on a minty fresh engine also, not one that already had 5 owners and beat every mustang in town.
The only 2 parts of the bottom end that keep the piston in line are the rod bolts and the piston pin.
Having a heavier piston in stock form basically vs any of the aftermarket as well as a heavier pin in the .945 vs aftermarket .927 then you can imagine the extra load the rod bolts take as they are not only stretched one way and then compressed the other, but the torsional shock load against their travel as each cylinder fires....its so much more than click..click on the torque wrench and done.
If making high performance rod bolts were easy there would be way more companies doing it...hell there would be way more chinese bolts on the market. Even the overseas companies use ARP. That says something. ARP knows well more than you or I on the subject. They have great writeups in their catalogs and on their site also.
02-20-2019, 09:17 PM
Definitive answer on ARP rod bolts on gen3 rods 
7k rpms on a fresh ls6 rebuild with ARP bolts and no resizing and no issues. Oil pressure rocks too. 
