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rod bolts query

Okay, I am halfway thru torqueing my ARP rod bolts. I did their 3 times at 35 ft-lbs on about 4 bolts and never could get the .0120 stretch. Usuall .0090-.0100. Retorqued incrementally and would check with stretch gauge. I had to torque up to 45 on one, only 39 on another. I think the amount of lubricant on the threads and face of the nut may cause some of this.

The late 2 bolts I went straight to stretch method, left the gage on and turned the wrench to get .0120 stretch.

Started me thinking, why do they specify an actual stretch amount and not strain? Each of my bolts is slightly different length, so why not specify a percent strain and then one would stretch to reach the strain.
Old 02-26-2005, 11:21 PM
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I've had the same experience with ARP and Raceware rod bolts i.e. the torque method didn't produce the specified stretch.

Thinking out loud, the "extra" bolt length that sticks out past the nut before torquing isn't going to be stretched so using a percentage length increase (strain) has it's drawbacks. The effectiveness of the stretch method would depend on the thickness of the parts being clamped (rods) being the same, not the bolt length. Does that make sense?
-Chris
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Old 02-27-2005, 12:27 AM
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My bolts have almost nothing beyond the edge of the nut to start with. Just taking the measured lengths and stretching them.0120 gives me strains of .004377, .004372, .004379, .004375, .004369, and .004378 for the 6 bolts I have done. Young's modulus is about 2 million psi so my stresses are from 8738 to 8758 psi. These bolts probably have a yield right around 12000. Any one know the strenght of these bolts?

thanks
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Old 02-27-2005, 01:12 AM
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where do you get a stretch gauge?
Old 02-27-2005, 06:55 AM
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The rod bolts would have to be fiberglas composite to have Young's modulus of only 2 million psi; a value of of 29 million psi or higher is more typical. The yield strength should be in excess of 150,000 psi; the "aerospace" fastener alloys like MP35N have even a higher yield strength. Depending upon the nut design one cannot assume all the threads within the nut are at full load and comparable strain. Much of the load (sometimes like 60%) is taken out by the first thread. Is the torque wrench you are using calibrated? I have seen them off by more than 40% especially at the upper and lower portions of their adjustment range.

Website with ARP bolt material strengths:

www.centuryperformance.com/fastenermaterials.asp#AERMET

Last edited by Jim Sims; 02-27-2005 at 07:06 AM..
Old 02-27-2005, 06:58 AM
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stevepaa...... Measuring bolt stretch is a much more accurate way of determining the clamping load vs torque. Given mass production even with quality hardware, there is bound to be differences in clamping load with one torque setting.

You mentioned 'lubricant' on the nut face, is this what ARP recomends? Also are you using a dial indicator to measure the bolt stretch?
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Old 02-27-2005, 08:47 AM
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ARP includes their own "special sauce" for lubricating the threads.
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Old 02-27-2005, 08:52 AM
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To all

Well, one should never start calculations when one should be in bed. Young's modulus should indeed be about 29 million psi. I should not look at overall length of bolt but only that part between faces of the rodends, i.e. that part that actually gets strained. Just assume no relative strain in nut section, and thus doing what ARP says is correct. Get strains of 0.005376 for all bolts, with stress at 156K psi. Yield is around 180K, or about .0138 on stretch.

Used the ARP lubricant, a little on the first and a lot on the last-should use a lot and be sure to put on face.

I would torque and then use stretch gauge. I would incrementally go up with torque and check with stretch gauge. Did that on first two rods.

For the rest I will stick to stretch, because by guessing at what the torque should be next applied to get to .0120 stretch, you can easily exceed the correct stretch. Need to stay below .0138 on stretch for insurance.

Thanks for the website on specs.

http://www.gearheadtools.com/13002.htm

For the stretch gauge. This works very well.

I would like to find a 12-point 11mm torque adapter to make this a little easier to do.

Now just going to use the torque wrench to 35 ftlb, which gets me to about .0100. Then use open-end wrench with stretch gauge attached to go to .0120.
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Old 02-27-2005, 11:54 AM
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You have very (un) simply stated why one should always use stretch and never use torque on critical fasteners. Torque is very very inaccurate and even following all the fancy footwork suggested by ARP could be off by hugh percentates, way more than you have experienced.

And marketing strikes again! Probably afraid that they might scare off a single customer ARP has bowed to marketing wizzards, probably the ones that came up with new coke, and put in a torque spec for people to cheep to buy a stretch guage or to technically challanged to figure out how to use one.

I just did a search for a stretch guage on Pelican, none found. So whats up? Someones missing a chance to sell something here. An alternate method to a stretch guage (which is a simple dial indicator arranged so that is can monitor the change in length of a bolt as its tightened) one can use a std micrometer (not a dial indicator). Its a bit more tedious as one has to constantly tighten, measure, tighten but not so much as to overdo it, the bolt. As soon as the bolt is the specified ammount longer, in this case 0.012", than where it started,it is done.

Using a stretch guage is much simpler, you just clamp on the guage and then using a std wrench tighten until you get the desired number. The guage gives a continuous readout of the progress. A quality guage will have sufficient spring pressure to stay securly in place.

http://www.tavia.com/01400_rod_bolt_stretch_gauge.html

I suggest the type of guage shown here. The main reason is that it is adjustable for almost any length rod bolt.

Another possible source of the tool is the ultimate special tool supplier used by the pros. Just hang on to your wallet though cause they ain't cheep. http://tools.baumtools.com/index.jsp?menu=german

more sources
http://www.precisionmeasure.com/block4.htm

http://www.silver-seal.com/Index.cfm?p=368
page146

http://www.faliconcranks.com/tool.htm

http://www.powerandperformancenews.com/store/merchant.mvc?Screen=PROD&Product_Code=POW101300&Category_Code=CONNECTINGROD&Store_Code=PH

The last one is a good one. Its spring is strong, an important factor in a stretch guage.


And finally for those who got more money than whatever and want the ultimate $1000 stretch guage, digital of course
http://www.tavia.com/01401_digital_rod_bolt_stretch_gauge.html

Last edited by snowman; 02-27-2005 at 06:03 PM..
Old 02-27-2005, 02:49 PM
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Quote:
Originally posted by snowman
I just did a search for a stretch guage on Pelican, none found. So whats up? Someones missing a chance to sell something here.
I will be working on that department in the near future...

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Old 02-27-2005, 04:45 PM
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Anyone used a "stretch" gage or some "stretch" methode when replacing rod bolts without splitting the case?
Thx.
-Henry
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Old 03-17-2005, 07:31 AM
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I suspect not. The stretch guage is difficult to attach and get around everything that gets in the way with the bottom end open. With it togather its probably near impossible.

If not opening up the bottom end I would use stock Porsche stretch bolts. These use a torque to angle method to tighten that can be readdily done with the bottom end closed. Please note that this torque to angle method differs from the one discribed by ARP in a very important way. ARP discribes using torque to angle with a reusable bolt which leaves it undertightened due to the necessary safety margins. However using stretch bolts, which cannot be reused, one thighens the bolt beyond its yield point, but just short of its breaking point. Its impossible to get more out of a bolt. The stock Porsche bolts are likely much better than an undertightened ARP bolt. Thats my opinion.

PS Its not possible to (safely) fully tighten an ARP bolt without using the stretch guage.

Last edited by snowman; 03-17-2005 at 08:05 PM..
Old 03-17-2005, 08:02 PM
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OK good info., thanks...I can rebolt the rods using Porsche torque to angle bolts and not split the case. The question at this point is...leave well enough alone or go deeper with changing and the $ and risk associated. The info. I've been getting is if you are not pushing the revs on the car no a track there should be no issues staying with the bolts in there right now. Comments welcome Ted and Don Wise will probably say stay away.. That's what they said on the p's and c's and they are now down at JWE...

-Henry
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Old 03-17-2005, 09:02 PM
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So whats your question? Whats the condition of the engine you are working on and what do you intend to use it for?

If you stick to Porsche redlines you will do well with all original Porsche parts, track or street. Thats what the car was designed to do. But if you are RACING thats differen't. But not to worry, most of us do NOT race we just do track time. There is a BIG difference, a factor of 10 on dollars, mininum, if you Race the car. If you have to question if you are racing or tracking a car, the answer is YOU are tracking the car. YOU will KNOW if you are really racing. HOW? because you have already tracked the car to death, you now have more knowledge than someone asking this question, you just KNOW. IE if you have to ask you are tracking it.

Other ways to know if you are a RACER. Your engine cost over $30K, you are using Carillo rods, you have done EVERYTHING you can to the suspension and to remove weight, the car cannot be driven on the street, you need 110 octane race gas as a MININUM, your redline is 8K plus and you often exceed it. YOur tires have 2/32 when they are NEW, your wife starts to know the REAL cost of your parts.

Last edited by snowman; 03-17-2005 at 10:16 PM..
Old 03-17-2005, 10:09 PM
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I'm not racing just everyday driving and AX, one or two DE events per year....I haven't moved the redline from stock and don't plan to....so I guess I don't need to worry about the rod bolts currently in the car. It is probably the case that a lot of people reading on this forum are racing and assumed I was going to be racing.
-h
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Old 03-17-2005, 10:43 PM
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Snowman et al (who is Al, anyway?!),
just an f.y.i., here's a nice way to measure bolt stretch http://www.norbar.com/products_category.php?category_multid=8
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Old 03-22-2005, 09:41 AM
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Quote:
Originally posted by galwaytt
Snowman et al (who is Al, anyway?!),
just an f.y.i., here's a nice way to measure bolt stretch http://www.norbar.com/products_category.php?category_multid=8
That doesn't look cheap...
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Old 03-22-2005, 04:14 PM
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I know I'm not the only one who's has experienced 3.2 rod bolt failure - without "racing" (by Jack's $$$ definition). My take on it is that every time you miss a shift or "zing" the RPM's high enough, you run the risk of stretching the bolts. The effect is cumulative; eventually the rod clearances open up enough that you pound the bearings out. EDIT: I did a lot of track events prior to the failure.
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Last edited by ChrisBennet; 03-22-2005 at 05:45 PM..
Old 03-22-2005, 05:39 PM
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Chris,

If you were really racing, as opposed to tracking, you would have experienced the failure in the first or second race, not after a lot of events.

Are you running wheel to wheel? If not you are NOT racing. Racing is a whole bunch of cars all on the same track all starting at the same time and only the first car to cross the finish line after a pre determined time or number of laps is the winner. There are usually a mininum of 20 continuous laps involved. Timed runs are NOT racing. Only in racing do you see your opponent trying to pass you, and you him, and only in the heat of that battle are you really RACING.. and the heat of the battle is very very important, because thats what seperates the men from the boys. Thats when the engine gets a new redline, thats when the brakes get tested at their limit, thats RACING;

Only several HUNDREDS of cycles are required to break a bolt, if you have exceeded its clamping force.

Last edited by snowman; 03-22-2005 at 08:39 PM..
Old 03-22-2005, 08:22 PM
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Snowman..........with all due respect, that's a bit over-simplistic. Example? - rallying, or sprints, against the clock. (I believe it's the SCCA championship in the US), but we know the event type as "WRC". Not uncommon to have fractional-second differences over 10/20/30 stage miles.

You couldn't say someone in that sphere wasn't 'racing', or to be more accurate, that their engine would be any less stretched by that activity than being on a circuit as per your description.

"Track days", on the other hand, at least the connotation here is, owner/drivers in street cars getting the opportunity to use a real circuit. Fear, insurance and mechanical calamity all usually conspire to restrain you ever-so-slightly, so that circumstance, I'd agree, is less onerous than 'pure' bona-fide racing.........
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Old 03-23-2005, 02:55 AM
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