measuring rod bolt stretch & preload

grumpyvette

Administrator
Staff member
http://arp-bolts.mobi/p/tech.php?page=3

http://arp-bolts.mobi/p/tech.php?page=2

http://www.hotrod.com/how-to/engine/116 ... etch-tool/

http://arp-bolts.com/

http://www.harborfreight.com/1-inch-tra ... r-623.html

http://garage.grumpysperformance.com/index.php?threads/precision-measuring-tools.1390/#post-44530

read the factory shop manual or connecting rod manufacturers info VERY carefully...FT LBS AND NM ARE NOT THE SAME
http://www.kylesconverter.com/torque/newton-meters-to-foot--pounds-force

IF you do some careful shopping you'll find that decent connecting rods are available at semi reasonable prices, I would insist on 7/16" ARP rod bolts and 4340 forged steel, and suggest SCAT, as a lower cost but good value connecting rod source




bustedvl.jpg

you'll
need accurate precision measuring tools

http://garage.grumpysperformance.com/index.php?threads/precision-measuring-tools.1390/
18512.jpg

http://www.amazon.com/T%C3%BCrlen-Indic ... +indicator
dialtr.png

BTW IF YOUR SEMI SKILLED AT FABRICATION, AND HAVE THE SKILL AND PATIENCE,
a $3 C clamp and a $15-$45 dial indicator some set screws and some time on a drill press and a few taps ETC.,( AFTER THINKING IT THRU CAREFULLY OF COURSE) can make you a fully functional rod bolt stretch gauge for peanuts, rather than spending the $60-to-$260 a factory produced stretch gauge commonly costs

17225a.jpg


AS AN EXAMPLE
867125aa.jpg

DIYRodBoltStretchGauge11087565341.jpg

http://www.slidewright.com/kuu-3-way-cl ... 7Aodkh0Amg
http://www.summitracing.com/parts/arp-1 ... /overview/ $248
http://www.summitracing.com/parts/arp-1 ... /overview/ $186
yes you can find non-name brand rod bolt stretch gauges from about $50-$80

StretchGauges2.jpg

555-80591.jpg

ARP-boltssd.jpg

http://www.jegs.com/i/JEGS-Performance- ... Id=1130494
StretchPreload.gif

tqvsstr1.JPG

ARP rod bolts are set up to use a stretch gauge with both ends of the bolt pre-machined for the gauge the bolt packaging from ARP,comes with the correct length the bolts are supposed to reach under the correct pre-load tension, in the instructions OR its available on their web site
youll need a good quality torque wrench
torquewrench.png

and a torque angle gauge

41M70Tl7tKL.jpg

rodboltyg.jpg



rodboltyg1.jpg

ctrp_0901_19_z+limited_late_model+race_engine_build.jpg

most guys are familiar with use of a torque wrench to tighten rod bolts to the correct preload, but while this gets you very close its not as precise as a rod bolt stretch gauge,
ctrp_0901_18_z+limited_late_model+race_engine_build.jpg

23-0261RCUlr.jpg

116_0609_rod06_z.jpg

116_0609_rod01_z.jpg
 
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ITS mandatory that YOU as an engine builder be aware that theres a few machine shops that are run by scam artists willing , even happy to cheat the less informed customers, and the decepion and cost cutting saves them considerable money while basically providing you with a very inferior product at an inflated price.
IMPORTED parts from over seas being substituted for much more expensive, well known brand name components, DOES HAPPEN!
It helps your engine's potential durability tremendously, if you take the time and effort to verify that you have, and that if you have a machine shop do all or part of your engine assembly that they, actually had the quality components, you paid for installed in your engine, Ive had several machine shops try to pass off and install really crappy quality components in engines while charging top dollar for brand name parts.
now I'm sure that easily 70% -90% of the guys never bother to check what they got back from the machine shop for accurate machine work or that simple things like the bolts, studs and bearings , rings and gaskets the machine shop used during the engine assembly were actually the parts you paid for, but I know for a fact that less than honest shops don,t bat an eye over making a few bucks extra with this bait and switch B,S.
Ive seen connecting rods, main caps, studs rockers push rods pistons, piston rings, cranks and several other components being billed as name brand components and lesser quality parts actually installed!
there was a machine shop in Hollywood florida , that for decades was well known for this deceptive practice

ctrp_0901_18_z+limited_late_model+race_engine_build.jpg

example
fakearp1.png

fakearp2.png

fakearp3.png



RULE#1 if your not sure about some aspect of engine assembly or clearancing,

STOP!.. do your research, ask questions and get info from a couple reliable sources before proceeding further
check your factory shop manual for torque specs or contact the connecting rod manufacturer,


https://racetoolsdirect.com/product...MI-cu3zOzv3gIVi4nICh1iVgDKEAQYASABEgJ2AvD_BwE
PFM66788-600x400.jpg

https://www.amazon.com/JEGS-80591-B...159417&sr=8-3&keywords=rod+bolt+stretch+gauge

(my choice in a rod bolt stretch gauge)
41Tgz5IYJ6L.jpg

https://www.summitracing.com/parts/pow-pow101300/overview/
POW-POW101300.jpg

http://www.eaglerod.com/mosmodule/bolt_torque.html

What Do I Torque the Bolts To?
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.
boltdiagram.jpg

The following chart shows the head of the bolt, the dimensions, and the proper torque spec. Be careful! the heads of some bolts look similar and some even have the same markings. DO NOT identify the bolt by the head alone. Verify dimensions also! If the head of your bolts do not match one of the pictures below - you do not have Eagle rods! Please consult the manufacturer of your rods for proper torque specs. Their torque spec is most likely different than ours! Always use ARP moly lube on the threads and under the head of the bolt when torquing!
871500head.jpg

material
socket
size
under
head
length
thread
size
torque
8740
7/16"
1.500"
3/8"
40 ftlbs
871600head.jpg

material
socket
size
under
head
length
thread
size
torque
8740
7/16"
1.600"
7/16"
63 ftlbs
871700head.jpg

material
socket
size
under
head
length
thread
size
torque
8740
7/16"
1.750"
7/16"
63 ftlbs
871800head.jpg

material
socket
size
under
head
length
thread
size
torque
8740
7/16"
1.800"
7/16"
63 ftlbs
201400head.jpg

material
socket
size
under
head
length
thread
size
torque
2000
3/8"
1.500"
5/16"
28 ftlbs
201500head.jpg

material
socket
size
under
head
length
thread
size
torque
2000
7/16"
1.500"
3/8"
43 ftlbs
201600head.jpg

material
socket
size
under
head
length
thread
size
torque
2000
7/16"
1.600"
7/16"
75 ftlbs
201800head.jpg

material
socket
size
under
head
length
thread
size
torque
2000
7/16"
1.800"
7/16"
75 ftlbs
191600head.jpg

material
socket
size
under
head
length
thread
size
torque
L-19
1/2"
1.600"
7/16"
79 ftlbs
191700head.jpg

material
socket
size
under
head
length
thread
size
torque
L-19
1/2"
1.750"
7/16"
79 ftlbs
ca1400head.jpg

material
socket
size
under
head
length
thread
size
torque
CA 625+
3/8"
1.500"
5/16"
32 ftlbs
 
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Holy Crap Grumpy.
China Imitation ARP Rod Bolts.

How Low can you Get ?
 
I have been holding off buying a Premium Rod Bolt Stretch Guage.
Need for My Pontiac V8 Crower Race Connecting Rods of mine.
Guys on Y.B. Racing forum recommends only JEGS OR ARP PREMIUM PRO ROD BOLT STRETCH GUAGES.

I Like the Homemade Rod Bolt stretch guage made from a C-clamp.
Nifty Idea.
 
I agree rod bolt stretch is extremely important but have only measured with a micrometer.

Not the most convenient method, but still workable.

Thanks
Randy
 
23-0261RCUlr.jpg


My Crower connecting rod bolt stretch gauge looks like this Dyers.
But I did not get a Starrtet Dial indicator with it !
Ultra Nice.
 
torque wrench vs rod bolt stretch gauge accuracy
I post these links hoping that most of the linked info is read and the related info is used or at least considered by the few guys who wish to become rather skilled and knowledgeable, in engine assembly.
no one has mastered all the skills and going back over even rather common assembly skills and looking for tips on how to improve existing procedures seldom hurts.
as time progresses, theres always on-going documented testing, and in many cases the old established way of doing things has proven to be less than ideal as newer and more detailed testing proves.
I well remember the advice in the later 1960s to keep end gaps on upper piston rings in the .004-.005 per inch of bore diameter, and secondary compression rings , to a tighter .04 max per inch of bore diam, as they experience less heat related expansion, the gaps could be tighter, well testing over the last 40-50 years has proven that approach to be less than idea, a looser .005-.006 second compression ring end gap is now been rather conclusively proven to work a bit better as it tends to lower and trapped combustion pressure, that could reduce the top rings bore seal.
strechgy.jpg


most engines using nearly stock rod designs with arp rod bolts don,t seem to suffer a bit using a torque wrench, if you use the correct tech and lubes
arp-ultra-torque-fastener-assembly-lubricant
if as previously mentioned, the rods bolts are tightened and loosened three successive times and torqued to the recommended
torque suggested
yes I generally use a rod bolt stretch gauge on anything built for serious performance,
but as the chart above illustrates the difference in the results is not huge in most cases.
btw most ARP rod bolts use 12 point nuts, so a 12 point deep socket
ctrp_0901_19_z+limited_late_model+race_engine_build.jpg



https://www.xtremediesel.com/arp-ul...MIiN_xkvT05QIVCY6zCh2Z2Af3EAQYAiABEgJnNfD_BwE


100_9910_ARP_web_updated_600x600.jpg

116_0609_rod01_z.jpg


https://www.enginelabs.com/engine-t...easuring-rod-bolt-stretch-vs-torque-with-arp/

https://www.hotrod.com/articles/using-rod-bolt-stretch-tool/

http://garage.grumpysperformance.co...ng-rod-bolt-stretch-preload.11050/#post-85102

http://www.performanceenginetech.com/connecting-rod-bolts-stretch-vs-torque/


stretch-gage.jpg

Connecting Rod Bolts – Stretch vs. Torque
Today I’d like to discuss the proper method for performance connecting rod bolt installation. There are a few ways to tighten connecting rod bolts, including the basic torque method, the stretch method, and the torque to yield method. Without a doubt, bolt stretch is the only truly accurate way to establish proper bolt preload. To better understand why, we need to look at how a bolt works.

Understanding Stretch
A bolt functions similar to a spring, in that it needs to be stretched beyond it’s static length in order to apply a clamping force. In the case of a connecting rod bolt, the clamping force must exceed the tensile load imparted by the attached components during high rpm operation. This is accomplished through a combination of bolt material selection and stretch dimension.


A common method for determining ideal stretch, is by incrementally increasing the amount of stretch until the bolt becomes permanently elongated. This dimension is termed yield, and a typical target stretch range is then determined to be 75-80 % of yield, with the min/max provided to the end user at +/- 5 % of this target. As an example:

  • Yield = .007″ stretch
  • Target stretch is 75-80 % of yield = .0052″ – .0056″
  • +/- 5 % of target = Min/Max of .0049″ – .0059″ (recommended stretch range)
Yield varies, and is affected by a variety of factors, such as material, bolt length, under-head register length, and shank diameter.

Proper Use of Torque
As explained above, what we really want to do is install the rod bolt at a near optimal percentage of yield in order to apply as much clamping force as possible without putting the integrity of the bolt at risk. Using a torque wrench to tighten the rod bolts in your high performance engine is a risky proposition, unless you are willing to invest some effort into quantifying the readings.

Torque in regards to bolt tightening is just the amount of force required to overcome incremental increases in friction. Torque readings (friction) are affected by thread quality, composition of lubricant, and surface finish of the bolt spot-face machined on the cap of the rod. Beyond the friction variables, not all torque wrenches – or users for that matter, are created equal.

I have used nearly every type of torque wrench available, and have a very high quality calibration unit at my disposal. The only torque wrenches that are consistently correct throughout the scale of readings, are high quality dial type. The ever-popular “clicker” type wrenches rarely apply the torque that the user has dialed in, and the higher the torque, the more it’s off. With that being said, they will torque consistently, just not the proper amount of torque.

Torque vs. Stretch
Now that we understand that the stretch value is what needs to be achieved, it’s necessary to verify what amount of torque on the wrench being used is going to stretch the bolt within spec. All rod manufacturers provide an information sheet that will list the recommended torque spec and bolt stretch range. Here’s the process I use to match my torque wrench reading the proper stretch value:

  • Install the cap on the rod with the manufacturers recommended lube on the bolts.
  • Carefully draw the cap into the rod using a nut-driver alternating from side to side in order to keep everything square until the cap & bolts are properly seated.
  • Loosen one bolt just enough to be sure there is no load on it.
  • Install the bolt stretch gauge on the loose bolt.
  • Set the dial to “0” – remove and re-install gauge to verify it still reads “0”
  • Remove the gauge.
  • Finger tighten the loose, just measured bolt.
  • Torque the opposing bolt to 25 ft. lbs. – this assures it has a small amount of preload on it.
  • Torque the measured bolt to the manufacturer’s recommended value.
  • Install the stretch gauge, and see what the bolt stretched to.
  • If the bolt isn’t within specs, loosen and adjust torque up or down until you reach the desired stretch.
  • If the bolt is stretched within the specified range, loosen the opposing bolt and repeat the measure/torque/verify procedure.
  • Repeat these steps to 4 bolts to assure that the same torque reading provides the same amount of stretch.
At this point you should be able to use the torque wrench reading determined in the outlined process to torque the rest of the bolts, or continue to stretch each bolt individually. I should also be clear that you must zero the dial on the stretch gauge for each bolt. The center dimples used for the gauge are not a critical dimension, and will vary from bolt to bolt.

That’s all for today. I hope I’ve cleared up any of the mystery surrounding proper rod bolt installation for you. As always, I look forward to your feedback, questions, or comments. You can comment directly to this or any other article on the site or send me an e-mail. Please invite your friends to join us, and thanks for visiting …..




https://www.enginelabs.com/engine-t...easuring-rod-bolt-stretch-vs-torque-with-arp/

http://www.performanceenginetech.com/connecting-rod-bolts-stretch-vs-torque/


http://garage.grumpysperformance.com/index.php?threads/unforgiven-project.15214/page-53

https://arp-bolts.mobi/p/tech.php?page=3

http://garage.grumpysperformance.co...ng-and-basic-piston-ring-info-youll-need.509/

http://garage.grumpysperformance.com/index.php?threads/what-con-rods-would-you-buy.942/

https://www.hotrod.com/articles/using-rod-bolt-stretch-tool/

http://www.superchevy.com/how-to/engines-drivetrain/49258-rod-bolt-torquing-stretch-info/


https://ecatalog.mitutoyo.com/Spindle-Attachment-Tip-C1129.aspx

 
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my internet connection was out for about 24 hours yesterday due to a lightning storm, damaging the local telephone networks.
so I took the time to go over to a friend's shop and B.S. , drink coffee,
and help him finish assembling his BBC engine.
he was at the point of assembling his rotating assembly.
watching him use the stretch gauge was both mildly entertaining and frustrating,
I found he had no idea how to set the rod bolt length with the Allen key on the lower
rod bolt.
he had previously pre-assembled the rotating assembly,
to check all the clearances so that was done correctly.
yes you can assemble an engine using just a torque wrench and plasti-gauge and get reasonably good results,
but to be precise and get max durability and clamp values,
use of a stretch gauge on rod bolts is recommended


related threads and sub linked info

yodam.jpg


http://garage.grumpysperformance.co...lling-the-steel-crank-shaft.16345/#post-99022

http://garage.grumpysperformance.com/index.php?threads/a-few-basic-precision-tools.16344/#post-99006

http://garage.grumpysperformance.co...-about-your-potential-dream-bbc-combos.14607/


http://garage.grumpysperformance.com/index.php?threads/a-few-questions-on-bearings.14466/#post-75272


https://www.bar-tek-tuning.com/arp-rod-bolts-installation

https://www.adperformance.com/index.php?main_page=product_info&cPath=304&products_id=904

http://garage.grumpysperformance.co...tion-of-crank-durring-short-blk-assembly.852/




Scat Rod Bolt Torque Specifications

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ROD TORQUE SPECs

IMPORTANT INSTALLATION INSTRUCTIONS

1. Disassemble rods and thoroughly clean (including bolt and beam threads) to remove rust preventative.
2.
Apply ARP Molylube to the threads and under the head of each bolt.
3.
Install rods by bringing cap and beam into alignment. Tap into place before installing bolts (DO NOT USE BOLTS TO PULL CAPS INTO POSITION) Each rod is numbered and MUST be assembled with the same number on cap and beam.
4.
Sequentially torque bolts to specified torque NOT TO EXCEED maximum specification for stretch.
DESCRIPTION


RECOMMENDED
TORQUE
NOT TO EXCEEDSTRETCH



5/16" x 1.500" ARP 2000 cap screw 26 ft./lb w/ARP moly (.0056" stretch)
3/8" x 1.600" ARP 8740 cap screw 45 ft./lb w/ARP moly (.0047" stretch)
3/8" x 1.600" ARP 2000 cap screw 50 ft./lb w/ARP moly (.0058" stretch)
3/8" ARP 8740 Wave Loc bolt & nut
50 ft./lb w/ARP moly

(.0063" stretch)
7/16" x 1.400" ARP 8740 cap screw 64 ft./lb w/ARP moly (.0046" stretch)
7/16" x 1.500" SCAT 2001 cap screw 63 ft./lb w/ARP moly (.0050" stretch)
7/16" x 1.600" ARP 8740 cap screw
63 ft./lb w/ARP moly

(.0050" stretch)
7/16" x 1.600" ARP 2000 cap screw 70 ft./lb w/ARP moly (.0062" stretch)
7/16" x 1.800" ARP 8740 cap screw 63 ft./lb w/ARP moly (.0060" stretch)
7/16" x 1.800" SCAT 2001 cap screw
63 ft./lb w/ARP moly

(.0060" stretch)


watch the videos
he had a proform stretch gauge
https://www.summitracing.com/parts/sca-26700716/make/chevrolet
sca-25700_w.jpg

s-l640.jpg

similar to the one above,
I watched him as he was using a long box end wrench and the stretch gauge
and a digital torque wrench to get the bolts very close to the correct preload,
and then verified the bolt stretch with a stretch gauges and a long box end wrench

https://www.enginelabs.com/engine-t...easuring-rod-bolt-stretch-vs-torque-with-arp/
555-80591.pdf

ctrp_0901_19_z+limited_late_model+race_engine_build.jpg

we brought the rod bolts up to the suggested torque readings

https://www.jegs.com/installationinstructions/500/555/555-80591.pdf
https://hotrodenginetech.com/how-to-tighten-stretch-a-rod-bolt/


ARP%20ADVANTAGES%20OF%20WAVE-LOC%20ROD%20BOLTS.GIF

materials-chart.jpg

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ctrp_0901_18_z+limited_late_model+race_engine_build.jpg


Aftermarket Connecting Rod Manufacturers
Rod Manufacturer Tech Support # Website
Argo
+61 (02) 4934 7099 (Australia) argorace.com.au
Arrow Precision +44 (0) 1455 234200 arrowprecision.com
Bill Miller +1 (775) 887-1299 bmeltd.com
Brian Crower +1 (619) 749-9018 briancrower.com
CAT +1 (626) 330-1999 catpep.com
Callies +1 (419) 435-2711 callies.com
Crower +1 (619) 661-6477 crower.com
Dyers +1 (815) 657-9970 dyersrods.com
Eagle +1 (662) 796-7373 eaglerod.com
EARP Machine +1 (928) 428-3835
GRP +1 (303) 935-7565 grpconrods.com
Howards Cams +1 (920) 233-5228 howardscams.com
K1 Technologies +1 (440) 497-3100 k1technologies.com
Lunati +1 (662) 892-1500 lunatipower.com
Manley +1 (732) 905-3366 manleyperformance.com
Molnar Technologies +1 (616) 940-4640
Ohio Crankshaft +1 (937) 548-7113 ohiocrank.com
Oliver +1 (616) 451-8333 oliver-rods.com
Pauter Machine +1 (619) 422-5384 pauter.com
RPM +1 (562) 926-9188 rpmmachine.com
R&R Machine +1 (941) 621-8143 rrconnectingrods.com
Saenz +1 (305) 717-3422 saenzgroup.net
Scat +1 (310) 370-5501 scatcrankshafts.com
Swanson +1 (574) 858-9406 spmtitaniumrods.com
Wagler Competition Products +1 (812) 636-0391 email Wagler
Wossner +1 (865) 862-5264 wossneronline.com
ZRP Europe +30 2108251640 zrp-rods.com
 
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http://garage.grumpysperformance.com/index.php?threads/rod-bolts-rpm-vs-stress.341/

http://garage.grumpysperformance.co...onnecting-rod-rod-length-too-stroke-info.510/


https://www.hotrod.com/articles/using-rod-bolt-stretch-tool/

.https://www.cpgnation.com/how-to-measure-bolt-stretch-for-proper-torque/




main-caps.png

Stretching Exercise
What Is Rod Bolt Stretch and Why Do You Need to Do It?
Jeff Smithwriter
Jun 3, 2004

For decades, engine-builders have been tightening rod bolts with a torque wrench and getting away with it. But in today's high-performance world where we push engines to make a ton more power and spin at higher engine speeds, merely tightening rod bolts with a torque wrench is no longer the best way. In order to know why rod bolt stretch is a more accurate way to install a bolt, we have to get into a little bit of fastener basics.


P12CHARTS.jpg






Bolt Basics A fastener works like a coil spring. As you tighten a bolt, it will stretch and generate a clamp load. The key to proper tightening of a fastener is to torque it until just slightly less than the bolt's elastic limit. A bolt will stretch slightly as it is tightened. If you tighten the bolt too much, it will stretch beyond its elastic limit. If you measure a bolt's overall length before you overtighten it, then again when you release the preload, the bolt will be slightly longer. This is similar to overstretching a coil spring. It does not return to its tightly packed position because the steel has been stretched and over-yielded. This is the bolt's yield point, where it is permanently deformed. It's the point just before it comes apart. The bolt's ultimate tensile strength is the maximum stress imparted on the bolt before it breaks.










This applies to all fasteners, but it's especially critical with rod bolts because they're the most highly stressed fasteners in an internal combustion engine. With every revolution, the crankshaft yanks on the piston and rod assembly to pull it away from top dead center (TDC). The rod journal pulls on the rod cap, which tries to stretch the rod bolts. This stress becomes greater as engine speed increases since this load increases geometrically with rpm and forces the rod out of round, bending and fatiguing the bolt.



The key to keeping the rod cap on the rod is the amount of load created with the rod bolts. If the load created by the bolts is greater than the tension created by the crankshaft rod journal trying to pry the cap off the rod, then the engine will stay together. If the bolt is not properly preloaded (understretched) then the high-rpm tension is enough to stretch the rod bolts a very tiny amount with each revolution. This high-speed cycling of the bolt is similar to bending a paper clip back and forth until it breaks. That's obviously something you want to avoid.

Torque vs. Stretch The torque spec applied to any particular fastener is merely an estimate of the twisting force required to achieve the correct amount of preload or clamp load. Many times this is the only way to apply fastener load because the bolt threads into a blind hole like in the cylinder block. One advantage to the rod bolt is that both ends of the bolt can be accessed. This allows you to use a rod bolt stretch gauge. This is a specialty tool sold through companies like ARP that will accurately measure the amount of bolt stretch.




The procedure is actually quite simple. Once the connecting rod and cap are installed on the crank, start a nut on the rod bolt, slip on the appropriate-size box-end wrench, and then install the stretch gauge. All ARP connecting rod bolts have a small dimple placed on both ends of the bolt that accurately position the rod bolt gauge pins on the bolt. Next, zero the gauge on the relaxed bolt. Then you carefully tighten the rod bolt until the gauge reads the appropriate stretch amount. For example, a standard 11/32-inch ARP small-block Chevy specs out at 0.0063 inch.

ARP generally sets the stretch figure at 75 percent of the bolt's yield or elastic limit. This creates the most load with still plenty of safe "headroom" between the stretch figure and the bolt's limit. One advantage to measuring bolt stretch is that this figure is unaffected by whatever lubrication you place on the threads. This is not the case when using a torque wrench.

Stretch vs. Lube When you tighten a rod bolt nut using a torque wrench set to a specific spec, the wrench is measuring a resistance to movement. This resistance is partially the result of bolt stretch, but the majority of effort required to torque the bolt comes from friction. This friction results from the threads moving against one another as well as the rod bolt nut against the rod cap. This friction changes based on the type of lubricant used. For example, friction will be greatest with no lube and slightly less if oil is applied to the threads and the bottom of the nut. It will be reduced even more if you apply some of ARP's bolt lube to the threads and the face of the nut. The lube's friciton "index" is referred to as its friciton coefficient.

Perhaps you can see where we're headed with this little exercise. If you were to apply the same torque to a fastener with no lube and then use different types of lube, the stretch on the bolt would increase with the ability of the lube to reduce friction. This is why it is extremely difficult for a fastener company to give an accurate torque spec that will properly stretch the bolt because there are so many lubrication friction coefficient variables. If you must torque a rod bolt, ARP offers a torque spec with its lube.

Better Bolts ARP offers three different styles of rod bolts for most applications with increasing tensile strength for each version. The standard ARP high-performance 8740 alloy chrome-moly steel bolts offer a tensile strength of roughly 200,000 psi and are good for most all street-oriented applications. The Wave-Loc ARP bolt is the next level up using the same heat-treated 8740 steel but has patented symmetrical waves incorporated into the bolt shank that fit snugly into the rod without the knurling that can cause sharp edges and a stress riser that can cause a crack to eventually form.

ARP's best bolt is the Pro series Wave-Loc that uses higher-strength ARP2000 material with a tensile strength of approximately 220,000 psi. This higher-tensile-strength bolt is offered as an upgrade for ultimate competition engines that experience ultra-high rpm use such as Pro Stock or endurance road racing.

Now you know a little more about the stresses imposed on a connecting rod. For example, a 434ci small-block with a 4.00-inch stroke will generate a massive 3,200 g's at TDC at 6,500 rpm. Multiply the weight of the piston and the small end of the rod by this g-force and you can get an idea of the tension exerted on a connecting rod and its two bolts. Think about that the next time you want to just torque your rod bolts instead of stretching them the way you should.


It's also a good idea to measure the overall length of each rod bolt in the engine before torquing. Then when the engine comes apart, you can measure the bolts again. If the bolts all measure the same, you can safely reuse them. If one is stretched even just 0.001 inch, immediately replace the bolt.
 
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