Author Topic: Rod torque- all most blew it  (Read 1388 times)

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gregaba

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Rod torque- all most blew it
« on: June 01, 2022, 01:04:04 PM »
Finished my mock up on my 428 last week and was starting my assembly day before yesterday.
I bought Scat H beam rods with cap screws to use with accu tech piston'e.
I torqued 7 rods to the factory 40-45 ft lbs spec. Lost two of the rod retainer clips so stoped the assembly while I wait for the replacement's to arrive.
While thinking about it last night I was concerned with the stock torque spec not being right for the cap screw bolt's.
I went ahead and dug though all my instructions and found the Scat rod info sheet and fount I need to torque them to 63 ft/lb's.
So I guess the lesson is to read the instruction's.
Greg

Falcon67

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Re: Rod torque- all most blew it
« Reply #1 on: June 01, 2022, 01:52:22 PM »
Buy and use a rod bolt stretch gauge.  My H beam ARP2000 bolts required 78 ft/lbs to get the .006 spec.  Not the 60 something listed in the docs

351crules

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Re: Rod torque- all most blew it
« Reply #2 on: June 01, 2022, 03:24:36 PM »
i dont understand the need to stretch rod bolts. no other bolts are ,so what makes rods so special

jayb

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Re: Rod torque- all most blew it
« Reply #3 on: June 01, 2022, 03:54:55 PM »
Torquing a bolt is always designed to stretch it.  For a lot of bolts, it is not possible to measure the stretch (e.g. head bolts, main cap bolts, etc.), so a torque specification is all you can go by.  But since you can measure the stretch of a rod bolt with a gauge, it is always best to go that route.  I have seen the same issues as Chris, where in some cases the correct stretch requires more torque than the manufacturer specifies.  But for years I never used a rod bolt stretch gauge, and never had a bolt related failure just using the torque specs that the manufacturer provided.  So I don't think I'd get too worked up if the rod bolts were just torqued to spec, without measuring stretch.  Probably not going to be an issue.
Jay Brown
- 1969 Mach 1, Drag Week 2005 Winner NA/BB, 511" FE (10.60s @ 129); Drag Week 2007 Runner-Up PA/BB, 490" Supercharged FE (9.35 @ 151)
- 1964 Ford Galaxie, Drag Week 2009 Winner Modified NA (9.50s @ 143), 585" SOHC
- 1969 Shelby Clone, Drag Week 2015 Winner Modified NA (Average 8.98 @ 149), 585" SOHC

   

RustyCrankshaft

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Re: Rod torque- all most blew it
« Reply #4 on: June 01, 2022, 05:07:35 PM »
i dont understand the need to stretch rod bolts. no other bolts are ,so what makes rods so special

Every bolt is stretched - that is what actually retains the bolt. Rod bolts are just one of the few applications where it's easy to measure the actual stretch. Measured torque is the next best thing when you can't measure stretch directly. Since most bolts are made to one of a couple different industry standards, the engineering has been ballparked so we know that on a particular grade and size bolt that XX torque will = a certain stretch.

Some of the larger MTU engines I've worked on the main studs are "torqued" by using a hydrualic cylinder to stretch it and the "nut" is just spun down to the saddle by hand and the cylinder released. The first time you do one it's a bit unnerving watching a stud that bit visibly stretch! There are other engines that employ a similar process for certain fasteners. Also not uncommon in certain crane applications as well.

You don't need to measure stretch directly on rod bolts, it's just more accurate.

cammerfe

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Re: Rod torque- all most blew it
« Reply #5 on: June 01, 2022, 09:46:57 PM »
Well said, RC. Why not do the best job you're capable of?

KS

mike7570

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Re: Rod torque- all most blew it
« Reply #6 on: June 01, 2022, 11:40:55 PM »
Torquing a bolt is always designed to stretch it.  For a lot of bolts, it is not possible to measure the stretch (e.g. head bolts, main cap bolts, etc.), so a torque specification is all you can go by.  But since you can measure the stretch of a rod bolt with a gauge, it is always best to go that route.  I have seen the same issues as Chris, where in some cases the correct stretch requires more torque than the manufacturer specifies.  But for years I never used a rod bolt stretch gauge, and never had a bolt related failure just using the torque specs that the manufacturer provided.  So I don't think I'd get too worked up if the rod bolts were just torqued to spec, without measuring stretch.  Probably not going to be an issue.

When you can’t measure stretch some engines require a minimum number and then you add torque angle. Kind of hard to do in the engine compartment of a 2000 V6 Camaro where most of the engine is under the cowl and you need to get to a specific angle without repositioning the wrench. btdt.

Falcon67

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Re: Rod torque- all most blew it
« Reply #7 on: June 02, 2022, 09:17:20 AM »
Quote
But for years I never used a rod bolt stretch gauge, and never had a bolt related failure just using the torque specs that the manufacturer provided.  So I don't think I'd get too worked up if the rod bolts were just torqued to spec, without measuring stretch.  Probably not going to be an issue.

Agree here - same.  Lotsa rod bolts done with a regular torque wrench.  I'll just say that once I looked harder at the specs on upgrade parts and tried the stretch gauge, it was kind of an eye opener LOL.  Agree that in all likelihood, following the mfg torque specs will be good. I beat hell out of my stuff, so I try to do anything I can to be more accurate during assembly.

pbf777

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Re: Rod torque- all most blew it
« Reply #8 on: June 02, 2022, 11:30:19 AM »
     Just a note:  Yes, rod bolt stretch is the goal of the torquing process; and measuring the stretch directly is often considered more accurate in establishing the goal, if solely as is removes the bulk of the variables of the turning friction from the observation.  But in using the bolt-stretch method, also note that often the manufactures will state: "but don't exceed a turning torque value of............"   :-\

     The problem here is that we're looking so hard at the theoretical 'ideal' process, that we are at times surpassing the manufactures ability to control the consistency of the product, and each process being discussed has it's own unique advantages (and disadvantages!  :o ) to acquiring the end result. 

     Therefore, I find that I will often utilize both processes, on the single fastener, and at times balancing each to a, as I believe, best compromise.   8)

     Scott.

gdaddy01

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Re: Rod torque- all most blew it
« Reply #9 on: June 02, 2022, 09:20:45 PM »
no one uses the elbow popping method ?

BattlestarGalactic

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Re: Rod torque- all most blew it
« Reply #10 on: June 03, 2022, 01:47:13 PM »
From back when all we had was the old beam style torque wrench to measuring the bolts to within a few thousandths.  We've come a long way for sure.

When I check stretch, you can usually find a happy torque value to pull them down and get it close.  That is kinda my way to verify there isn't a bolt that is out of spec(bad manufacturing, heat treat, etc).  Usually it's about 5+ lb/ft more then what the old book calls for but that usually depends on how accurate the wrench is and the lube, etc.  So I just pull most of them right to that number, confirm stretch and go to the next one.

I watch a video of a guy working on a bit Cat engine.  They torque the main caps to XXX lb/ft and then take it 1/2 turn(or so).  Since it's hard to find a torque wrench to go that far and even harder to pull something like that while laying on the ground they figured a basic torque to yield way.  I did the rear springs on my Mack years back and had to pull the U bolts to like 600 lb/ft.  What a bear that was.  Had to borrow a buddies BIG torque wrench, then had to try to support it off the ground so I could reach out and pull it, and pull it, and pull it......ugh.
Larry

Stangman

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Re: Rod torque- all most blew it
« Reply #11 on: June 03, 2022, 03:11:29 PM »
Larry get yourself a torque multiplier. You get 600 ft lbs and it feels like 50 lbs. At our age it’s like cheating.

galaxiex

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Re: Rod torque- all most blew it
« Reply #12 on: June 04, 2022, 08:43:29 AM »
no one uses the elbow popping method ?

No....


I have a calibrated wrist.  ;)   ;D   ;D   ;D
Every 20 minute job is 1 broken bolt away from becoming a 3 day ordeal.

gdaddy01

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Re: Rod torque- all most blew it
« Reply #13 on: June 04, 2022, 02:59:57 PM »
must be the new improved version.

BattlestarGalactic

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Re: Rod torque- all most blew it
« Reply #14 on: June 06, 2022, 05:03:39 PM »
Larry get yourself a torque multiplier. You get 600 ft lbs and it feels like 50 lbs. At our age it’s like cheating.

It was like 15 yrs ago and basically a one time deal so a buddy just lent me the big wrench.  I was a bit younger and dumber then too....LOL.
Larry