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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
70 lb-ft (per Jegs instructions) is just standard torque for a 7/16 bolt. Not even remotely close to yield unless the shank is necked down or something.
Edit: Sorry guys, I goofed up big time with the units!
70 Nm (52 lb-ft) is standard torque.
80 Nm (59 lb-ft) is high torque.
Jegs is doing something special pushing those bolts higher.
Was the Ghost of Christmas Past secretly heat cycling and stretching them before they were packaged for sale???
The bolts that yielded and the ones that snapped were used bolts out of a GM assembled marine 383.
From memory I have had maybe 2 or 3 of these newer bolts start to yield before the final torque value is reached that were brand new in maybe 50 installations.
70 lb-ft (per Jegs instructions) is just standard torque for a 7/16 bolt. Not even remotely close to yield unless the shank is necked down or something.
When I started trying to explain why those bolts broke the way they did, I found both a Engine Rebuilder article by Jeff Smith and a video regarding the machining process of both the washers and newer cylinder heads allowing the washers to potentially spin. I was not aware of this problem until after the bolts were installed in that engine. Even after I sanded the ARP washers I have since installed on that engine a couple actually started to spin around 30-40 ft/lbs. I stopped the torquing process and then started to torque again. The washers stopped spinning and did not spin again during the process. So apparently even sanding the washer does not completely eliminate the potential for the washer to spin if you are not keeping a close eye on it. It is something I will definitely watch out for in future builds on any engine with washers under the bolt heads.
My basic stock type stuff will continue to get NEW GM or Felpro bolts. They have been relatively trouble free for me with only a handful of bolts that started to yield before reaching the specified torque angle. Once I went away from the 22/44/66 ft/lbs specs or the old 65 ft/lbs spec and started using 22 ft/lbs plus so many degrees on those bolts I cannot say that a single new one has stretched on me. I put these bolts on new many times at the standard SBC 65 ft/lbs without failure then something changed. The install method did not change, the bolt did.
I have tons of used bolts and a junk block. I will attempt both torque methods on used bolts to find out if either is successful. Most of the used bolts I have are out of stuff newer than the 96-99 engines. I have some out of mid-late 2000s GM crate engines that had the heads upgraded, several sets out of marine engines that were freeze cracked that I tore down for internal parts and I think even a set or two of used Felpro bolts.
So one thing that just came to mind is that coatings on bolts has been changing the last 20 years because of government restrictions of chemicals. Bolts aren't the same as they used to be. And coatings have a surprisingly big affect on friction during tightening. I wonder if changes of coatings are part of the issue here?
I highly doubt anybody is doing the technical analysis on the bolted joint when they sell bolts for an application. And that stuff is a deep topic matter, don't kid yourself. You'd get that kind of discipline with OE current production, but not legacy / aftermarket stuff - not until there's a problem big enough to hit their wallets.
Was the Ghost of Christmas Past secretly heat cycling and stretching them before they were packaged for sale???
Strictly talking about Vortec replacement bolts here. 2-3 bolts in maybe 50 installations started stretching when torqued to 65-66 ft/lbs. Perhaps it was due to the use of the alternative method rather than the preferred TTA method. In that timeline somewhere around the time I had a few starting to fail, I switched to the TTA method. From memory I have not had a NEW bolt fail using the TTA method. As for a used one, I have a bucket of used bolts and a junk block and I will test that soon.
So one thing that just came to mind is that coatings on bolts has been changing the last 20 years because of government restrictions of chemicals. Bolts aren't the same as they used to be. And coatings have a surprisingly big affect on friction during tightening. I wonder if changes of coatings are part of the issue here?
I highly doubt anybody is doing the technical analysis on the bolted joint when they sell bolts for an application. And that stuff is a deep topic matter, don't kid yourself. You'd get that kind of discipline with OE current production, but not legacy / aftermarket stuff - not until there's a problem big enough to hit their wallets.
I do not know if I would call this "legacy" production. GM still builds the 5.7L Vortec for many applications and it is still very much a valid production engine for them. It is still in the Marine and Industrial power line ups as well as replacement engine and performance engine line ups. I would venture to say that GM has probably built more Vortec 5.7L engine as Marine, Industrial and Performance engines than they ever built for truck applications. 96-2000 for US trucks, 96-02 for the vans, a year or two longer for a few specific other US vehicles and then up until 2007 in Mexico in the GMT800s. However they have built the Vortec 5.7L Marine, Industrial and Crate engines nearly continuously since 1996. I know they recently moved the process back to the USA from Mexico and that put a temporary stop to production as well as a massive price hike in those engines.
* There's no argument that it is a bad idea to re-use TTY bolts.
* You're not having trouble with new bolts.
So what is the point of all this argument? Seems like a lot to do about nothing.
The argument is whether or not Vortec head bolts are TTY. One source shows they are and another source shows they are not. At this point it is really more trying to ascertain the current fact of the matter. I personally will not re-use them myself. That is a decision I will firmly stand behind now and forever. Especially given multiple failures I have personally witnessed re-using them or attempting to.
If numerous more used bolts fail before they reach torque specification and GM Service Parts and Felpro are still claiming they are not TTY that is a HUGE problem, IMO. If GM has updated these engines to TTY like the Mercruiser manual section, I read a while back indicated and someone is servicing a GM Goodwrench crate engine that is in a 96-99 truck that could be disastrous to that engine.
The argument is whether or not Vortec head bolts are TTY.
vorteciroc said they were TTY when he was at GM. I think you won the argument a long time ago.
And for those who don't know or believe vorteciroc that's their loss. The guy is an engineer's engineer and even has something around 1600 Hp Vortec in his own car. He's been around these engines a bit....
It may be off the specific topic but I've seen no mention of what type of lubricant is used during the torquing process.
I can't recall the last time I used an OEM head bolt so I'm out of the loop there however, ARP, as you're all aware I'm sure, has their own lube and specific torque chart for their bolts when their lube is used. IIRC, their spec does not match the engineers handy reference guide to torque specs for bolts of various sizes and tensile strengths.
Well I'm not reading all that, just skimmed some...
Still I wanna add, back in college we had to pull apart grade 8 bolts for a metallurgy class, using this big machine and then test the hardness of each bolt. It was interesting to see how some would really stretch before failing and others would just go a bit n pop. Was a cool class, learned a lot and it was taught by an old NASCAR guy. Said every team that he ran, the first thing he would do is replace every bolt on the car with at least grade 8, even if they just held in the dash.
vorteciroc said they were TTY when he was at GM. I think you won the argument a long time ago.
And for those who don't know or believe vorteciroc that's their loss. The guy is an engineer's engineer and even has something around 1600 Hp Vortec in his own car. He's been around these engines a bit....
No offense meant to vorteciroc, don't know him but...
I know plenty of guys with fast/high power cars who don't know jack. It's funny to see them BS their way thru stuff when you know what's what. Still don't try n tell the fool asking them unless your faster cause that is all that matters to them LOL I like slow cars myself for various reasons most people can't understand so I won't try to explain.
It may be off the specific topic but I've seen no mention of what type of lubricant is used during the torquing process.
I can't recall the last time I used an OEM head bolt so I'm out of the loop there however, ARP, as you're all aware I'm sure, has their own lube and specific torque chart for their bolts when their lube is used. IIRC, their spec does not match the engineers handy reference guide to torque specs for bolts of various sizes and tensile strengths.
No lubricant under the face of a stock bolt. Felpro actually states that in plain english in their instructions. The instructions state as long as they have the factory thread sealer on them to install them as they come out of the box. The coating they apply does the rest.
It may be off the specific topic but I've seen no mention of what type of lubricant is used during the torquing process.
I can't recall the last time I used an OEM head bolt so I'm out of the loop there however, ARP, as you're all aware I'm sure, has their own lube and specific torque chart for their bolts when their lube is used. IIRC, their spec does not match the engineers handy reference guide to torque specs for bolts of various sizes and tensile strengths.
There is a reason my ARP studs are now torqued to their old 65 ft/lbs specification rather than the new 80 ft/lbs revised spec. Same stud, same material and a lubricant that makes nuts spin a stupid amount more easily and they want 15 ft/lbs more than the old method using aluminum heads. They are also completely ignoring the added expansion of aluminum heads. I saw the new spec of 80#, questioned it as being insane and did several hours of research on the subject. I found literally dozens of cases of threads being pulled at 80 ft/lbs and even personally looked at a distorted block deck from that process being followed.
I can't comment on head studs as I don't use them.
ARP suggests 70 ft lbs with the assembly lube and their head bolts.
That said, even a 70 ft lbs, I feel the threads in the blockare going to give out. They've seen, under my stewardship, at least a dozen re and re's. And the block is a late 70's vintage. Might be Heli-Coil time this spring when another "final" assembly takes place.
70 lb-ft (per Jegs instructions) is just standard torque for a 7/16 bolt. Not even remotely close to yield unless the shank is necked down or something.
Sorry guys, I goofed up big time with the units!
70 Nm (52 lb-ft) is standard torque.
80 Nm (59 lb-ft) is high torque.
Jegs is doing something special pushing those bolts higher to 95 Nm (70 lb-ft), or they screwed up the units too.
Originally Posted by QwkTrip
It takes a lot to break a bolt on the spot, I mean waaaaaay out of bounds to snap one off.
Heres what I think basic on engineering courses I've taken
When a structure goes plastic, the load can be removed and then re-applied and it will go right back to where it was with the same load. Yielded is considered failure but the structure only deformed, it didn't break. For ductile that just means it won't return to it's original shape when load is removed.
IMO with bolts that means we can re-tighten a plastic tty bolt to its previously plastic point and take it a little bit further, stretched a little more, and it will function as if it never was used in the first place.
That means it can't follow the original tightening procedure- we have to manually feel the point the bolt behaves like plastic without any guideline for torque or angle.
Which is why its a bad idea for people to re-use them, unless they know what they are doing.
I don't think heat cycling causes stretch because if it did all the bolts would continue to stretch and they will all break after so many cycles. If it caused a little bit of stretch, thats fine, because we are taking it past that point the next time we used it anyways. The dangers are taking it too far, and taking it too little. There is a 'just right' amount whether doing for the first time or second time. If you care to take the risk for a $20 set of bolts.
Heres what I think basic on engineering courses I've taken
When a structure goes plastic, the load can be removed and then re-applied and it will go right back to where it was with the same load. Yielded is considered failure but the structure only deformed, it didn't break. For ductile that just means it won't return to it's original shape when load is removed.
IMO with bolts that means we can re-tighten a plastic tty bolt to its previously plastic point and take it a little bit further, stretched a little more, and it will function as if it never was used in the first place.
That means it can't follow the original tightening procedure- we have to manually feel the point the bolt behaves like plastic without any guideline for torque or angle.
Which is why its a bad idea for people to re-use them, unless they know what they are doing.
I don't think heat cycling causes stretch because if it did all the bolts would continue to stretch and they will all break after so many cycles. If it caused a little bit of stretch, thats fine, because we are taking it past that point the next time we used it anyways. The dangers are taking it too far, and taking it too little. There is a 'just right' amount whether doing for the first time or second time. If you care to take the risk for a $20 set of bolts.
The heat cycle I mention was merely the action of engine parts like the cylinder heads expanding with each warmup. Cold bolts are also more brittle than ones up to operating condition. The bolts are worked in operation vs holding tension in a static manner. Where an oil pan bolt (talking SBC with a flimsy stamped steel pan not some engine where the rigid cast pan is a structual member to the engine like a LS) is subject to very little force during the engines operation, main cap, rod bolts and head bolts are exercised with every combustion event and crankshaf revolution.
Cold steel being brittle is why I will never subject an engine that is not up to operating temperature to WOT or higher rpm. It more quickly fatigues parts like connecting rods and the crankshaft. That is in addition to oil pressure possibly rising far above the bypass point that could even blow the oil filter apart or at the minimum add substantial wear to the oil pump drive.
Since we are on the subject of bolts and hardware use and failure. I seem to remember a skyway bridge in a shopping mall collapsing a number of years ago. It was up north somewhere, maybe in the great lakes or canada area, I forget the exact details. But it killed and injured a large number of people. The failure was traced back to the hardware used to anchor and support it into place and engineers under estimating the forces involved. Point being even skilled engineers make mistakes.
The fastener Torque Spec is ONLY one factor.
Fastener Material (differences in stretch, and different types of strength) type of lubricant which helps to try an reduce the effect of other variables) condition of the engaging Threads, Head Gasket Material and Crush, repeat use of a fastener and even more...
I used to be naive and trusted instructions from companies.
Eventually I learned where these numbers come from and keep a cheat sheet in my garage to double check any instructions I'm reading. If it doesn't pass the "laugh test" then I'll pause until I figure out what's going on. You gotta do that with places like BMR, UMI, and such that are fab shops and not engineering groups. GM torque specs always seem to align with my cheat sheets.
I don't have a cheat sheet for TTY bolts though. I'm not even sure that's possible since it's special design. Or if there are standards then it's something I haven't seen yet.
Also in regard to using a Stretch Gauge to torque Fasteners (like Connecting Rod Bolts)...
Many of the Engine Builders that build high power output Engines (3,500 HP - 15,000 HP) no longer use a Stretch Gauge to torque Fasteners.
They have gone back to using purely a Torque Spec, and see far fewer Bolt failures.
When reusing Fasteners... it is common to measure stretch, but only to a Torque Value lower than the final Torque Spec.
This is done to make certain that the Fastener has not been stretched past it's maximum value prior to being tightened to the final Torque Spec.
After discussing this with other Engine Builders...
I started to do the same, and I have also seen fewer failures this way.
vorteciroc said they were TTY when he was at GM. I think you won the argument a long time ago.
And for those who don't know or believe vorteciroc that's their loss. The guy is an engineer's engineer and even has something around 1600 Hp Vortec in his own car. He's been around these engines a bit....
Qwk is always too kind.
I also have built an Alcohol Funny Car for myself... I finished it about 11 years ago, and have just updated it as NHRA has made annual Rule and Safety changes.
I can't not drive it any more, but still follow all the annual updates that NHRA releases.
Anyway my point is... I do not have much experience with these Cars, as I do not build them for my customers.
So I look to others that have a significant amount of experience.
I always listen to what they have to say, and then form my own opinions after doing all the necessary research.
There will always be others out there that factually know more than ourselves.
Learning is an enjoyable process, and I recommend that you guys remain open minded about continuing to learn more from others.
Just do your best to try and verify what you have learned as best as you can.
FYI i used a set of Jegs head bolts with thread sealer and torqued to 70 on my C3. Then pulled the heads with little run time about half a year later due to the M-shop getting all the exh guides too small. I cleaned up and plan to reuse those bolts.
Also I bought a 96 4x4 Sierra with a vortec 350 and plan to reuse those bolts as well, tho I'm not sure if the engine or trans was orig as their was signs someone has been in there. I considered making a vid testing those bolts, maybe torque and remove them 5-10 times but for the amount of work and little views it'd get, meh I don't care enough.
I once asked ARP how many times their bolts could be reused and their answer was as long as they are not damaged.
Oh and my project truck BUCK has new Fel-Pro head bolts that I'll reuse someday, was gonna use em on diff vortec heads with some Pioneer head bolt washers I got But now gonna get a set of Summit heads. So think i'll use those jegs bolts for that, if they look like the fit is good. We'll see when I get them.
...Said every team that he ran, the first thing he would do is replace every bolt on the car with at least grade 8, even if they just held in the dash.
That is not a universal truth. I spent nearly 20 years working for a division of a Fortune 50 company which made fasteners, custom and OEM forged products, and significant value-added assemblies of those.
I can inform everyone that not all fasteners are the same. A premier example is the fastener used to attach seat belt and shoulder restraint anchors to the body of a vehicle. There are strict federal standards for the performance of these, and manufacturer had an accredited metallurgical laboratory and NIST certified test facility, including the specialized equipment to test just this ONE fastener application. Those must stretch and must both yield torsionally and deflect axially up to a minimum standard. A little bit of thought would provide clarity as to why this is, since it is far better to have a seat belt bolt stretch, twist, and deflect under severe instantaneous shock loading than hold on until it snaps from exceeding its embrittlement tolerance (as is determine in a Tinius tester). I can also inform everyone that a restraint system meeting those standards will actually result in a 2" wide belt cutting a human body in half long before it fails and yields under tension.
The OEM engineers had to meet these criteria, just like they did for the other parts and assemblies on their vehicles. The aftermarket does not.
Similar standards applied to the hard-rolled main cap bolts, titanium valve spring retainers, rocker studs, intake bolts, numerous body fasteners, ball joint sphere elements w/stud, etc. The factory HAD to get it right for the factory stock vehicles. Once modifications start, all bets are off.[/u]
I was over at the shop a while ago. Since this thing is a junk block anyway. I put the used head gasket on the block. Set the cylinder head on. Then put those used bolts into the block. Using the GM/Mercruiser/Kohler alternative method of 22/44/66 ft/lbs they claim you can do in-frame rather than the TTA procedure. Out of those 17 used bolts, 5 of them would not reach 60 ft/lbs on the digital reading, they kept stretching, very obvious feel of the bolts yielding, 2 of those 5 snapped in half!!! Thats right 5 of them would not go to the specified torque value of this procedure and 2 of them snapped in half. When one broke I moved to the next one, as I said, junk block anyway. I checked the calibration of the torque wrenches before testing. Yes, I have a torque wrench calibration tool. Finally, I put on my 1/2" digital torque wrench adapter in addition to the wrench itself. The torque value was as precise as I could make it. I have seen some guys post that these bolts should go to 100 ft/lbs without yielding and even possibly pull the block threads without yielding. That would be true if they were not TTY! Tomorrow will be the main cap bolt attempt, since they too are claimed to be TTY. I already have the rotating assembly out of the block, so it will be throw the caps on it and go. If the bolts break, so what. One of the two that broke was the short bolt I posted the picture of too. Further enforcing the idea that it was stretched as GM built it.
I'm not taking sides and dont even care a whole lot about this particular topic, but I just want to applaud you for going out to your shop and performing an actual scientific experiment. Everyone loves to argue back and forth with theories and opinions, but few take the time to experiment and get their hands dirty to settle a disagreement or learn something new.
There, I posted something positive on the forum this year. It's a Christmas miracle.
Post/reply, article or video I always question results. Especially these days where science is for hire and you can find a study to say the opposite of another study but we won't get into all that.
Still as the internet goes, if something commonly FAILS then we will hear about it A LOT! Unless it's censored of course, websites with sponsors(even some forums). Still that is not the case here, they are just factory bolts.
Now then this is where the majority rules applies and works well in my opinion. You can find decades of data on forums. Of course the results will never be 100% because some people are gonna F-it up no matter what. Usually because of some factor they don't see/understand/consider. The quality control classes I took in college were pretty boring But one thing has always stuck with me(well other than the story bout the factory worker who by-passed all the safety measures and crushed himself) and that was to Keep asking WHY until you find the answer. Like peeling back an onion's layers.
Anyways forums aren't the most scientific as many arguments are EGO driven, why I always prefer/suggest outside data be used to settle these arguments. Also one of the reasons I decided to not perform a test and share it here because I am biased since I participated in it. And to make sure most didn't question my results(some always will), meh I got better stuff to do with my time and i would share it even if I didn't like the results. I feel in this case that the majority of past forums post, pre this discussion support my opinion and that is good enough for me. As I said in a prior post, the numbers who have DONE what is disputed is Proof enough!
At the end of the day they are trying to achieve a certain clamping load to keep the bolted joint from loosening. Part of the reason for the higher torque might be because of clamping load loss when the gasket creeps (compresses) after tightening. Basically overshooting so it's right after everything relaxes some.
The bolt itself has clamping losses from "set" too, which is the threads embedding after tightening which results in the bolt getting a tad bit shorter and more loss of clamping load. A bolt that stretches more has less set and experiences less loss of clamping load. This is one reason why stronger bolts are not necessarily desirable. So when people talk about this and that bolt being stronger.... it's not necessarily a good thing.
Using special high torques risks some bolts failing. If you take a batch of bolts and plot Applied Torque vs. Turn Angle, you would see most the curves are nearly overlaying and bundled pretty close to each other in the elastic region up to what is considered standard torque levels. At special high torque, but still in the elastic region, the curves begin to separate some (results vary more). And once beyond plastic the results go all over the map. Problem is some of those bolts in the batch will become plastic before reaching special high torque, and those bolts will keep turning and eventually break without reaching torque spec. It's just risky business running really high torques which is why TTY bolts are specially designed.
Bottom line is we don't know what is the best answer because we're not able to do a detailed bolted joint analysis. It's much more complex than looking at bolt proof strength and torque specs. That's why this discussion will never come to anything.
Bolts or studs do not stretch from combustion. Heads do not lift, they squish or creep, mostly aluminum. Otherwise defective bolts sometimes fail(break), block threads sometimes fail, blocks sometimes fail(distort), gaskets sometimes fail or metal sometimes melts.
MLS gaskets are designed to allow for movement, so they can re-seal after distortion.
The whole thing is highly misunderstood and I don't claim to be an expert or understand it entirely But I have talked to many and read a lot about it.
Used TTY bolts stretched less, have higher yield and max load than brand new TTY bolts.
I am hoping that those measurements were a mean taken from many of the same type of Bolt in each category...
and NOT just one of each Bolt.
I find this interesting as I do not use OEM fasteners at all...
I also do not follow always follow the ARP recommended Torque Values.
Different Cylinder-Blocks (I most use Dart for this application)/ Deck thicknesses...
Different Gasket Materials (MLS, Copper with recessed Stainless O-Rings, Etc)...
Different Cylinder-Head deck thicknesses...
Different Cylinder-Pressures/ Boost Pressures...
Different Fuels, and Cylinder Temps...
Fastener Material and Lubricant...
All factor into what I will use for the Torque-Spec.
Ask me how I know... It has a lot to do with Nitro-Methane.
I have seen Cylinder-Heads and Screw Super-Chargers launched over 100 Ft in the Air.
When I read what he posted, I knew it was not correct too. The heads are clamped into place and then the Bolts/Studs have to withstand a force equal to or greater to the force that pushes the piston down in addition to the preload force of clamping the head into place. Combustion chamber in the cylinder head typically having more surface area than the piston itself.
I am hoping that those measurements were a mean taken from many of the same type of Bolt in each category...
and NOT just one of each Bolt.
They did the test the way I would do it, sample size greater than 3 for each bolt for statistical t-test P < .05.
The method they used is one which I am extremely familiar. For example, my lab published a paper which uses this method, we use for tissue strength comparison. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8144998/
There is load cell, force is applied, results are given in a reproducible quantitative manner for analysis. It is very difficult to screw up this kind of very simple, common test.
The results are convincing to scientists and engineers. The results are logical, deviation is similar within groups, the way data was collected and graphed is ideal.
There is no way to produce a more convincing set of results for this type of experiment. If somebody does not believe this result, then, they are merely unfamiliar with scientific method, statistical evidence, and engineering experiments.
This experiment would easily convince a committee of doctors evaluating the work of a researcher.
They did the test the way I would do it, sample size greater than 3 for each bolt for statistical t-test P < .05.
The method they used is one which I am extremely familiar. For example, my lab published a paper which uses this method, we use for tissue strength comparison. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8144998/
There is load cell, force is applied, results are given in a reproducible quantitative manner for analysis. It is very difficult to screw up this kind of very simple, common test.
The results are convincing to scientists and engineers. The results are logical, deviation is similar within groups, the way data was collected and graphed is ideal.
There is no way to produce a more convincing set of results for this type of experiment. If somebody does not believe this result, then, they are merely unfamiliar with scientific method, statistical evidence, and engineering experiments.
This experiment would easily convince a committee of doctors evaluating the work of a researcher.
Excellent!
Cancer Research is an area that I tend to stay away from (Too many Family Members lost)...
But I am no stranger to the NIH/ NLM, and it was a good read.
Finally someone is talking my language!
Thank you.
12-20-2022, 02:25 AM
