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Rod Bolt Stretch Guage

Engine Building Fundamentals

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Hi Folks,

Bought some eagle rods for my Honda H22 engine. The instruction said "Warning: If any other lubricant is used, the bolt stretched method must be used due to different visocsity".

So using the supplied ARP lube am I supposed to just torque to the recommend torque specs 43ft lb? Or should I still stretched the bolt to 0.0055"- 0.0059"?

I started to use the stretch method with supplied ARP lube (Applied on thread and bolt head) and is at 50ft lb torque and is getting 0.004" stretched. Stopped here as I should make sure I'm doing it correctly first.

hello I have never had a rod bolt do that they normally stretch approx the correct amount just under or on the recommended torque setting i would be double-checking the specs on the bolts. are they new bolts? the second video atached shows what you should do if you have the issue you have with your bolts

here is a couple of inks to checking rod bolts



Contacted Eagle Rods today and they say I can use ARP lube and stretch it to recommend stretch, but they recommend to just torque it to the torque spec of 43ft lb listed.

Um, seems Eagle are telling you to use two different methods that you've already found to be in conflict. Did they specify anywhere what the bolts are supposed to be made of, their grade of ARP?

[edit] I have been doing some checking, and there seems to be the "OEM" ARP bolts, and specially made ARP bolts for Eagle - the latter have EAGLE etched on the head. For the former, I'd use the ARP stretch spec' and for the latter the EAGLE torque figure, after burnishing.

The stretch to torque relationship is going to vary with the steel alloy the bolts are made from, and there can be several ARP alloys used for the same connecting rod. There will be some markings on the head giving the alloy the bolt is made from and this is critical, because it may be possible to over, or under, tighten them if the wrong value is used.

Have a read of these and see if it helps

https://arpinstructions.com/generaltorque.html - you will note that, even over just these three grades of bolts, the spec' torque varies by a great deal.



To summarise,

From Eagle - "Hardware: 3/8 ARP 2000 Bolts" but they also say "The first step is to identify which bolts you have. Eagle rods are offered with a variety of different bolts. Each of which has a different torque requirement. Proper bolt torque is paramount to rod strength and life. Eagle does not use "off the shelf" ARP bolts. Eagle has ARP custom make bolts to our specifications. DO NOT use torque specs for off-the-shelf ARP bolts. Here is a diagram of some important bolt identifying features."- source http://www.eaglerod.com/index.php?option=com_content&task=view&id=24&Itemid=25

From ARP - "ARP2000®: ARP2000 is an alloy steel that can be safely heat treated to a higher level, producing a greater strength material than 8740. While 8740 and ARP2000 share similar characteristics – ARP2000 is capable of achieving a clamp load at 220,000 psi. ARP2000 is used widely in short track and drag racing as an up-grade from 8740 chrome moly in both steel and aluminum rods. Stress corrosion and hydrogen embrittlement are typically not a problem, providing care is taken during installation.

From their (ARP) torque chart - "55" lbs.ft.

Not something I have experience of, but I understand failure is more likely from under torqueing.

Some recommend, with new bolts and/or connecting rods, to tighten and loosen them to 75-80% of nominal torque three times to help burnish the threads and give a more consistent torque/stretch figure before the final tighten with fresh lube - you could try that.

Reporting Back..

Got an email back from Eagle. They say I can use either the 43ft lb torque method or stretch. Torque will be different on whatever method i used.

Decided to go with stretch method using ARP lube and getting anywhere from 54ft lb to 57 ft lb to get correct stretch. Also, doing what Gord said helped a lot by torquing and loosen several times to burnish the new bolt thread.

So all in all, burnishing the threads helped a lot and with using the stretch method my torques specs were closer to ARP 55ft lb than Eagles 43ft lb.


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