How critical is rod bolt torque?
Thread Starter
Senior Member since 1492
Joined: Aug 2000
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
How critical is rod bolt torque?
I read on another forum about a guy who over torqued his 3/8 rod bolts to 60-65! Rec 50ftlb. Are the rod bolts trash now?
When I do mine should I buy a new torque wrench to assure accuracy? My wrench is about 20yrs old!
Thanks
Len
When I do mine should I buy a new torque wrench to assure accuracy? My wrench is about 20yrs old!
Thanks
Len
Le Mans Master
Joined: Feb 1999
Posts: 5,877
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From: Park Ridge IL
Re: How critical is rod bolt torque? (1970 Stingray)
Arguably the most critical fastener in an engine. Rob bolts can lead to potentially catastrophic engine failure if they are significantly either over- or under-torqued. Overtorquing can stretch the fastener beyond it's point of elasticity and cannot return back to it's original dimension. Undertorquing will not provide enough preload(stretch) on the fastener.
I'd recommend using a rod bolt stretch gauge if you have one. Using a torque wrench allows you to approximate the amount of bolt stretch, but this will allow you to directly measure it. The appropriate range is provided with the rod bolts, usually .0004" - .0006".
According to ARP, the suggested torque is 20% below it's maximum, which means those rod bolts you are referring to are trashed. As for your torque wrench, your machine shop can probably help you out in either testing or correcting it's calibration. If it was taken care of - never used to remove a fastener, always returned to '0' when not in use, and not abused, there's no reason it might not still be accurate. Only a calibration can test for sure though.
I'd recommend using a rod bolt stretch gauge if you have one. Using a torque wrench allows you to approximate the amount of bolt stretch, but this will allow you to directly measure it. The appropriate range is provided with the rod bolts, usually .0004" - .0006".
According to ARP, the suggested torque is 20% below it's maximum, which means those rod bolts you are referring to are trashed. As for your torque wrench, your machine shop can probably help you out in either testing or correcting it's calibration. If it was taken care of - never used to remove a fastener, always returned to '0' when not in use, and not abused, there's no reason it might not still be accurate. Only a calibration can test for sure though.
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,870
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From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Re: How critical is rod bolt torque? (Monty)
Thanks Monty. Now I'll know to pay careful attention when I do mine.
I'll be using a beam type torque wrench that I've had for about 20 years. Should I get a new one or can this one be calibrated? I don't think I've ever dropped it and take pretty good care of my tools.
Thanks
Len
I'll be using a beam type torque wrench that I've had for about 20 years. Should I get a new one or can this one be calibrated? I don't think I've ever dropped it and take pretty good care of my tools.
Thanks
Len
Le Mans Master
Joined: Feb 1999
Posts: 5,877
Likes: 1
From: Park Ridge IL
Re: How critical is rod bolt torque? (1970 Stingray)
A beam torque wrench is better than nothing, but a quality "click" type torque wrench is more accurate when properly used. I don't know if the beam type can be calibrated, other than insuring the pointer is at "0" before torque is applied.
If you're not going to be building engines very often, I'd just rent or borrow a "click" type wrench. The beam type is good enough for most other fasteners on a car - a few lbs of torque variation usually aren't as critical.
If you're not going to be building engines very often, I'd just rent or borrow a "click" type wrench. The beam type is good enough for most other fasteners on a car - a few lbs of torque variation usually aren't as critical.
Safety Car
Joined: Mar 2002
Posts: 3,780
Likes: 442
From: Southwest MI
Re: How critical is rod bolt torque? (Monty)
I agree with Monty 100%..... rods, and their bolting, are critical (most stressed area of the engine)....... If you plan on taking it over 6000 I'd get the best ARP's (Pro series, only a few $ more) and torque them per the instructions (you don't torque them as tight as weaker bolts)...... also have your rods reconditioned by someone into hi-performance, and I'd recommend a little polishing, it's easy/cheap. Whatever you do, don't go to a hacker, many rods end up weaker than before they were worked.
[Modified by 66427-450, 7:40 AM 12/27/2002]
[Modified by 66427-450, 7:40 AM 12/27/2002]
Racer
Joined: Aug 2002
Posts: 289
Likes: 0
From: Albuquerque NM
Re: How critical is rod bolt torque? (66427-450)
ls6 rods torque to 63 lbs no more than 70lbs....If you use the GM boron Bolts just do them to .009" stretch...(maybe 74lbs). I was under the impression that the idea was preload the rod to attain good bearing crush. shed some light here. :)
Thread Starter
Senior Member since 1492
Joined: Aug 2000
Posts: 87,870
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Re: How critical is rod bolt torque? (wallyknoch)
Thanks for the info guys. I'lll be using ARP bolts, they're brand new and I just read their recommendations. Torque the bolt to 50ftlb, then loosen, repeat x 3.
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Le Mans Master
Joined: Mar 1999
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From: delmont pa
Cruise-In I Veteran
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Re: How critical is rod bolt torque? (1970 Stingray)
always use a rod bolt stretch gauge because torque reading depend on the lube,feel and surface finish. you can then just use a box end wrench to do the rod bolts. :chevy
Safety Car
Joined: Mar 2002
Posts: 3,780
Likes: 442
From: Southwest MI
Re: How critical is rod bolt torque? (clem zahrobsky)
always use a rod bolt stretch gauge because torque reading depend on the lube,feel and surface finish. you can then just use a box end wrench to do the rod bolts. :chevy
:seeya
[Modified by 66427-450, 2:29 PM 12/29/2002]