FE Power Forums
FE Power Forums => Non-FE Discussion Forum => Topic started by: Hipopinto on November 07, 2020, 05:37:14 AM
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Hey all I have yet another question on my build
I have a very high quality set of connecting rods for my current build. These are American made 300m material dyers top rods brand with 7/16 ARP LA 625 D bolts
I’m using the supplied thick brown lubricant on the bolts
I’m noting some differences while assembling
Torque range on the card is 70-80 lbs but to get these to stretch to .0054-.0058 that range is all over the place
I have the bolt measurements recorded and I have not overstretched the bolts
Some rods stretch at about 70 lbs some stretch at 85 lbs I’m using a clicker MAC torque wrench to start then I pull them and measure
Am I making a mistake in this method?
Everything I read says stretch is far more accurate for fasteners but why do we measure stretch on rods but only torque on main and head bolts/studs?
I just want this little guy to live a long life while making a tremendous amount of power
Any feedback would be awesome guys
Thanks again
Dave
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How many times have you stretched each bolt? You will need to do it 2-3 times each bolt, each time putting lube on the threads and under the heads.
You will ultimately see some variation, so if you've cycled them a couple of times, just do whatever it takes to get to the correct stretch. On the higher end stuff I do, most of the bolts are torque-angle, and to get them to stretch the correct amount, sometimes you have to go 1-2° past spec.
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I had a bolt stretch vs torque value issue on a set of Eagle rods with premium ARP bolts. One of 16 bolts felt soft and came up to stretch at around 20 ft. lb. to low, even felt soft. I had pre torqued the bolts several times previous to assy. and re lubed each time with proper lube. If your bolts in question are not way out of range and do not feel soft through the wrench I wouldn't worry about it. I did not use that bolt.
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Another thought, pretty much impossible to measure stretch on main bolts and head bolts because of the blind holes.
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Another way that has worked with success, is to measure bolt stretch, and see what the torque was required to get there, and then torque all the bolts to that torque. We survived two world wars, multiple regional wars, built cars for over a hundred years, and now all of a sudden, we need to stretch our bolts for them to survive? Joe-JDC
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Another way that has worked with success, is to measure bolt stretch, and see what the torque was required to get there, and then torque all the bolts to that torque. We survived two world wars, multiple regional wars, built cars for over a hundred years, and now all of a sudden, we need to stretch our bolts for them to survive? Joe-JDC
I'm right there with you, Joe. I usually try to follow the suggested torque method by the manufacturer, but if one of the methods is torque or torque/angle, I'll go straight to that.
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Most of the OEM's are using rundown guns that measure torque and angle. We started doing that at Dearborn Engine in the early 90's.
Often they are used with torque-to-yield fasteners, but they work just fine with high quality standard pieces. If you're beyond the specified angle and the torque hasn't come up to the prescribed range, something is definitely wrong!
I remember doing a quality audit at the plant, and I watched a bunch of engines get kicked off the line for failing cylinder head bolt torque. Up comes the foreman, who looks around but doesn't see me. He grabs a big breaker bar, gives all of the cylinder head bolts a good tug, and sends the engines on down the line :o :o
So much for high tech fastener monitoring >:(
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That is precisely my thoughts
A few of these stretched in perfectly
Others are requiring a lot more torque to make it happen
So my question is at what point is torque correct or should stretch be the go to?
Also at what point in the automotive time line did we start measuring stretch? Did they do it in 1966?
I’m just curious as to how the stuff was done to compete in LeMans and Daytona back then
I just want this to hold together and not self destruct maybe I’m paranoid
Thanks
Dave
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Stretch is the most accurate way of checking something and when a company gives me a stretch number, then I'll use it. If it takes more than 70 to stretch it, then it takes more than 70.
I have a digital torque wrench that measures a myriad of different things. When I have a torque-angle spec, i.e. 30 lb-ft + 60°, it will read me the amount of total lb-ft it took to get to spec. That will vary 5-10 lb-ft sometimes.
With that being said, if you don't like the way something feels, then toss that bolt and buy another one. ARP makes most of the rod bolts out there, whether it be an entry level Scat rod bolt or an L19 Oliver rod bolt. They are available individually and I'll buy extras when I'm doing a $$$ refresh.
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Bolts made by the thousands and then heat treated will have variances depending on the accuracy of the manufacturing of the barstock material and the final heat treating process. Nothing is perfect when made in those large quantities.
I grew up with an old school torque wrench, and still have it. Agreed, it all works fine for the most part but stretch is just a high tech way to make things more accurate. Technology is great, but can drive you nuts in the use of it.
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Gotta agree with Larry Most repair shops don`t have the luxury or tools to do torque to yield. so out come the good ole torque wrench.
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Is it accurate to say that torque values are established to provide a desired amount of bolt stretch? Is bolt stretch what keeps a fastener from loosening?
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As a user, my first experience with anything HiPerf from Ford that had a documented stretch spec. was when Ford released the "SPS" rod bolts for the NASCAR connecting rods. Jack Roush gave me a set along with a small strip of paper imprinted with the stretch spec. My next question was how do I do this since stretch gauges were, definitely not a common item. His reply, "torque them 70 lb-ft with red lock-tite and don't concern yourself about the stretch spec..
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Bolts made by the thousands and then heat treated will have variances depending on the accuracy of the manufacturing of the barstock material and the final heat treating process. Nothing is perfect when made in those large quantities.
I grew up with an old school torque wrench, and still have it. Agreed, it all works fine for the most part but stretch is just a high tech way to make things more accurate. Technology is great, but can drive you nuts in the use of it.
Stretch is the most accurate measure of clamp load. Torque is an indirect measure, since it depends upon the integrity of the threads and the thread friction. If you have a burr on a thread, or you're using the wrong (or no) lube, the torque value will be way off. Likewise, if a thread somewhere on the bolt or hole (nut) is starting to shear, the torque value will go soft. Incorrect heat treating on the bolt does the same thing.
For super high performance fasteners, you want both stretch and torque to be in a known range. That's belt and suspenders - good threads and good material properties on your bolt. Stretch gauges have been around for a long time, but were limited to high end stuff. I think the DC bolt rundown guns came out in the 80's for production use, but didn't come into widespread use in OEM production until the 90's. Before that it was air guns and finish torquing with clicker wrenches.
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I'm not denying that stretch is the best method, but has anyone experienced, or even seen a failed engine due to a failed rod bolt? Even the stock stuff? I suppose it's happened, but I've never seen it with anything, big or small. That's good enough for me, although I'll replace any stock bottom end hardware these days for any performance engine. 40-60+ years of use is way beyond my comfort zone.
Using the wrong lube is a bonehead user mistake. A light burr on a thread should go away after a few torque cycles, which should always be done just to "set" the threads for a good torque reading. Any bad burring should be chased or replaced.
I've had bolts (not rod bolts in my cases) that suddenly went 'soft' when tightening. At that point you have to stop and carefully check the threads for pulling out, or toss the bolt if the threads are ok.
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I have seen a few cases where a rod bolt backed out, causing a cap failure. Mostly stock stuff, but one notable rebuilt SCJ engine. I'm with you Doug that it's pretty unusual for a properly torqued rod bolt to break. Now if you're re-using bolts it's another ballgame entirely!
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I once started to put a short-block together using a set of rods Carl Holbrook had done-up for me. Forging lines removed, polished, and shot-peened. Quality bolts and nuts. The one rod bolt seemed soft, and when I stopped and looked, the rod was crushing. Goodness knows what had happened, but the parting line was beginning to mushroom around that bolt. I took it back to Carl and he had another ready for me by the next day.
You never know what might be 'off'.
KS
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Ok
I will call dyers again today
I just ordered a long 7/16 boxed end wrench
Will try this again and see my results
Thanks guys
Dave
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What's the wrench for?
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I’m thinking to use it to keep a steady pull on it while leaving the stretch gauge in place
Bad idea?
Just thinking it would be easier for one person to do it
Dave
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I’m thinking to use it to keep a steady pull on it while leaving the stretch gauge in place
Bad idea?
Just thinking it would be easier for one person to do it
Dave
I don't think you're gonna be able to pull hard enough on a little wrench to get to 70 lb-ft. You also can't stop and start and stop and start. It takes more torque to break-away than on a steady pull.
It's just trial and error. Easiest with the rod out on the bench in a rod vise, loosen the bolt, zero your stretch gauge, then torque and recheck it.
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Pretty fond of the torque/angle concept.
An initial modest torque value gets things squared away and takes the "give" out of gaskets and assembly. Then the angle part of the process gives you an accurate stretch number without any fancy gauge or need for access to the other end of the fastener. It becomes a straightforward math problem - number of threads per inch and degrees of fastener rotation are always going to give you a fixed value.
Accurate statement about running a few tightening cycles to burnish the threads and underhead areas. If you pay attention you'll find that torque values and tightening feel gets smoother and more consistent after a few "go arounds". Anything that feels wrong or looks wrong needs to just get tossed. A hard lesson learned a long time ago...
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Another way that has worked with success, is to measure bolt stretch, and see what the torque was required to get there, and then torque all the bolts to that torque. We survived two world wars, multiple regional wars, built cars for over a hundred years, and now all of a sudden, we need to stretch our bolts for them to survive? Joe-JDC
This is what I do - cycle new bolts, check a set for torque to stretch, then run the all to that torque. IIRC, the H-beams in the 393 came around at 82 ft/lbs (vs 70 called) Ain't nut'in flown out the motor yet.
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I’ve done the wrench and stretch gauge on the bolt at the same time. It takes a GOOD 7/16” wrench with a cheater on it to make the roughly 80ft lb it takes. I got to where I could make the torque in one smooth pull. It also makes some nicely bent wrenches that work really good for big block header bolts Sucks that my collection got stolen and have to go back to regular straight wrenches. It would have been easier to use a torque wrench with the available bolt lube offered now as opposed to what I had on hand at the time
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I've had bolts (not rod bolts in my cases) that suddenly went 'soft' when tightening. At that point you have to stop and carefully check the threads for pulling out, or toss the bolt if the threads are ok.
Makes me think of when the impact's rpm suddenly goes through the roof and a nut turned into a fat washer... (no, I don't use an impact on rod bolts or anything else critical for that matter)
I'm not denying that stretch is the best method, but has anyone experienced, or even seen a failed engine due to a failed rod bolt? Even the stock stuff?
I haven't, personally. In fact I've never actually broken any engine part, and I've pushed several engines beyond their stated limits. Almost every catastrophic failure that I have witnessed was when a rod wanted to see daylight, but the failure point wasn't the bolts. One drag racing buddy I had managed to twist several rods in a 460 but they didn't snap, and the engine was still running. That one was bizarre. I can't think of what could ever twist a rod unless something got into the combustion chamber and magically got back out on its own.
Torque and angle is the main method we use on industrial automation projects, whether it is for trim panels or engine assembly.