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Old 04-13-2013, 08:23 PM
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Rod Bolt Stretch

So I am geeting conflicting reports about proper rod bolt torque. SBC ARP 3/8 bolts. Some saying 45lbs some 55 or more, provided you get .006 stretch. My question: If I use a rod bolt measureing tool, do you remove it each time and then add 5 pounds more torque and remeasure? How accurate is torque as to stretch?

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Old 04-13-2013, 09:24 PM
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Up to 50 ft lb on ARP.
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Old 04-14-2013, 06:31 AM
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The real way to do rod bolts is by stretch. You leave the gauge on the bolt, and using a box wrench, you slowly pull up on the bolt while constantly checking the stretch on the bolt
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Old 04-15-2013, 08:58 AM
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Unless they're the "Wave-Lok" or other "special" rod biolt, ARP says 50 lb. ft,., tightening and loosening twice before final torque. use ARP lubne...

FWIW

Jim
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Old 04-15-2013, 09:41 AM
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Properly torqued rod bolts will be within .0005" of the exact bolt stretch specification 99% of the time. If that is not close enough, use a stretch gauge.

Proper procedure:
Use the lube specified by the bolt manufacturer and an accurate torque wrench.
Bolt torque is a measure of friction.
Bolt stretch is a measure of tensile strength.

Bolt torque:
Torque the nuts twice - This polishes the threads on the nuts, bolts and the bearing surfaces between the nut and the cap.

Final torque the nuts to specification with a feeler gauge between the rods.
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Old 04-15-2013, 02:47 PM
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Quote:
Originally Posted by Richiehd View Post
So I am geeting conflicting reports about proper rod bolt torque. SBC ARP 3/8 bolts. Some saying 45lbs some 55 or more, provided you get .006 stretch. My question: If I use a rod bolt measureing tool, do you remove it each time and then add 5 pounds more torque and remeasure? How accurate is torque as to stretch?
Torque is used as a secondary way of measuring fastener stretch. It really is measuring the friction between the threads as well as that of the bolt head or nut where rotating contact is made with the surface of the object being clamped by the fastener.

There are tests perfromed by the manufacturer where the amount of torque is measured against the desired amount of stretch. The variable conditions of thread quality, contamination within the threads and heads, and the lubricant used in and under these friction points are documented. Simply put a typical OEM will specify undamaged and clean threads and points of contact from a bolt head or nut lubricated with fresh engine of a specific grade nets .000X amount of stretch for XX or XXX inch or foot pounds of torque. One can see the possibilites of arriving at a torque reading that does not result in sufficient stretch or produces excessive amounts of stretch. The latter often being the use of an unspecified lubricant. With ARP you need to check their specifications as often the torque they quote is with their proprietary lubricant where using something else will render the incorrect stretch for the indicated torque.

This quickly becomes a book size disscussion so I'll refer you to the link below for a 3 part story.

MEASURING CONNECTING ROD BOLT STRETCH (Part 1) Precision Engine

Bogie
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Old 04-15-2013, 03:31 PM
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Well Im really old!!! LOL The bolts I used for stretch torqueing always had a specific torque lets say 90 foot lb. and then an extra 1/2 turn or 3/4 turn added to reach a desired stretch Or Preload as we used to call it! We never stretched them then pulled them out to measured them and then re torqued them LOL!! I never heard of that? But over the years I guess things have changed But I still get into stretch torque areas of assemblys and its stipulated never to use the bolts twice!!!

Once a bolt was stretch torqued, a bolt or stud, we didn't use them a second time! They were already stretched! Once a stretch torque was achieved with a bolt if you keep stretch torqueing it more then once it can lead to failure! If ARP studs or bolts only have a specific torque you torque them at that. If they give you a specific torque and say add a 1/2 turn do that! Other then that I don't know what to add except call the manufacturer of your bolts and ask a tech! Dont ask opinions on here and try to choose what to follow by whoes opinion you think is right on something like this!! They have a tech line at ARP! There are no varying opinions on how every one thinks its done (even mine) that may be right or wrong!! There is only one answer and that is from the manufacturers specs! ONE ANSWER AND ONLY ONE there are no other ways to do it right!!!!! Thats just my opinion LOL

Jester

man my spelling check isn't working so excuse any errors please LOL
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Old 04-15-2013, 08:04 PM
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Had to leave when I last posted just got back from a 400 mile drive and just read oldbogies post Its dead on target

Jester
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