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Warren Hall Student
 
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What happened to Verbus rod bolts?

What happened to Verbus?

Accidentally posted in Tech forum. Can we no longer get Verbus rod bolts?
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Bobby

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Old 10-25-2016, 09:34 PM
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Bobby, I would't be surprised if the VERBUS name was no longer in use-- maybe for the VERBUS-RIPP locking fasteners, but not for the bolts anymore. Acument Global Technologies used to own that line (through a succession of companies that rolled into it) but their web site no longer shows the brand.

USPTO shows VERBUS as no longer an active mark.

Use ARP bolts.
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Old 10-26-2016, 02:51 PM
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Used to use SPS bolts way back in the day, but now use various ARP rod bolts, depending on the application.
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Old 10-26-2016, 03:27 PM
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Does Raceware still make rod bolts? High strength steel. Also made head studs. ARP seems to be the most common upgrade.

I once made a list of all the names/letters stamped on top of the regular bolts in my extensive collection scarfed from discarded VW and Porsche engines, trannies, and cars. VERBUS was prominent among the dozen or so. That was before the advent of Chinese fasteners.
Old 10-26-2016, 06:05 PM
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Yeah. I guess I'll be using ARP from here on out. I was always comfortable with Verbus for a street motor but I'd rather over build than risk some ill fitting rod bolt.
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Old 10-26-2016, 09:01 PM
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This may be a little off topic, but maybe someone with metallurgical engineering experience can explain the "only torque once" OE Porsche rod bolts.

I don't get it. If you torque a bolt it stretches. Creates tension. You un-torque the bolt it relaxes. You re-torque it, it stretches and is is tension.

The rhetoric with the OE rod bolts is "they are malleable". OK. So if you stretch a bolt to its elastic limit, fine. Why can't it be re-torqued to its elastic limit? That is within the bolt's capacity. If not it would fail during use. If you over torque a bolt, and go past it's elastic limit, to its yield point, wouldn't it be prone to failure?

Case in point. ARP rod bolts can be re-torqued and re-used. They are physically the same dimensions as the OE rod bolts.

So why are Porsche rod bolts one use only?

Rant over.....
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Old 10-27-2016, 10:40 AM
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I think it is nonsense - and is a throwback to the very early 901/01 engine.

In Volume 1 of the Workshop Manual the comment was made that the bolt should be replaced because it is 'malleable'.

There is always difficulty in translating Technical German to English and the description probably means that the bolt does exceed its it yield point and will permanently deform.

This will mean that the bolt will work harden to a new level of strength.

In simple terms and to a first approximation most steels obey a parabolic flow curve of the basic form:

Ơ = kƐ^n


Where Ơ = True Stress
Ɛ = True Strain
k = Strength Coefficient
n = Work Hardening Exponent

It is fairly easy to determine k and n experimentally if you have access to a tensile test machine.

If the steel does deform plastically it will follow the 'flow curve' defined by the above equation until it reaches the load level created by the applied torque.

If it is then unloaded it will not return to its original length but will have a small but measurable offset.

If the bolt is then re-loaded it will not yield again until it reaches the load to which it was last tightened hence the term 'work hardening'.

The elastic limit has effectively been re-defined and the bolt is now stronger than when first used. If the bolt is never used at loads greater than this level again it will IMHO be perfectly safe.

The simple way to check, which I have suggested in the past, is to measure the length of a used bolt with a stretch gauge prior to tightening and then torque the bolt.

Loosen the bolt and then re-measure the length.

If it returns to the starting length it is still elastic and good to go.

I would carry out this exercise 2-3 times and allowing for a little scatter and measuring error make a judgement.

It is also interesting to note that following the initial statement concerning malleability the comment disappeared in later volumes of the manual.

It does, however, still recommend changing nuts.

I do believe that all of the later Porsche Bolts are fully elastic within their operating range.

I have checked about 20 Porsche conrod bolts in this manner and have always re-used them.

If the preload applied to early bolts had taken them too far past their initial yield point then you could arrive at the situation where the bolt started to fail.

This is the point at with the reduction in area caused by the plastic strain being generated occurs more rapidly than the material increases strength due to work hardening. The elongation of the bolt after this point becomes non-uniform.

This is that dreadful point when the torque applied starts to fall as we continue to rotate the nut and we just know the bolt is about to break.

This is associated with the development of a visible neck within the bolt and happily is not too common for those of us that are not too hamfisted.

Last edited by chris_seven; 10-27-2016 at 11:46 AM..
Old 10-27-2016, 11:35 AM
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Thank you.

That makes perfect sense.

I guess all the books that say throw them away after once torquing them should have an *, Unless checked with new nuts.
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Last edited by Trackrash; 10-27-2016 at 05:31 PM..
Old 10-27-2016, 05:28 PM
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So now the question becomes: why do you need new nuts? Anyone known the nut to fail on a fastener (absent the threads being so boogered up you would never use it again because you couldn't thread it on with your fingers to start with)? Nuts must have elastic and plastic ranges, and yield points, too. But maybe they are well above those of the bolt or stud? Because their OD is much greater?
Old 10-27-2016, 10:40 PM
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The design of bolts and nuts is interesting and again I think Porsche recommend changing the nut because it is ‘malleable’ and they have again suggested a conservative approach.

Measuring a nut to be confident it undamaged is more difficult and they are less expensive to replace.

It is fair to say that the ‘proof strength’ of a nut is usually greater than the bolt it is used with and it is normally considered ‘better’ that the bolt fails rather than the nut because it is generally more obvious to identify.

It is normal practice, however, to manufacture nuts from a ‘softer’ material than the bolt as this would mean that if the threads in the nut did tend to yield then more of the threads in the nut would be used to support the load.

If the threads do start to yield then when the nut is removed there will be permanent deformation of the thread and if the nut is re-used its ‘pitch’ and form will mate differently to the thread in the bolt and this could have a significant and indeterminate impact on the relationship between torque and preload which in turn means critical fasteners could be under-tightened.

When faced with slightly damaged nuts (Ouch! ) we often blame the problem on ‘galling’ and tidy up the thread of the nut with a tap.

This changes the threads ability to transfer load and can often lead to catastrophic fatigue failures due to the altered load distribution in the modified thread.

The manner in which threads transfer load is a subject all on its own and is relatively complex.

I m not really sure what to make of Porsche’s comments but I would tend to think that if the nut spins easily by hand onto the bolt it is probably OK and wouldn't need changing.
Old 10-28-2016, 12:52 AM
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OK. So to clarify, one could;

Measure the length of the bolt.

Torque the bolt, again measure the length of the bolt.

Release torque, again measure the length of the bolt.

If it returns to it original length, it can be considered a good bolt. (?)

What if;

Measure every bolt.

Assemble rods and crank and torque all twelve rod bolts.

Measure every bolt.

Assume for this example that 11 of the bolts stretched .009". One bolt stretched to .012".

Can it be safely assumed we have 11 good and one bad bolt?
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Last edited by Trackrash; 10-29-2016 at 02:24 PM..
Old 10-29-2016, 02:19 PM
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Well, when you are measuring rod bolt stretch you don't use torque as your stopping point - you use stretch. Once stretched to spec, you have applied the required clamping force to the joint. It appears it is good practice to note the torque at which you achieved the stretch, because if you got the stretch on one bolt at a whole lot less torque, you would suspect that was a bad bolt. Unless you had wildly varying lubrication between bolts or some such other variable. I'll never forget torqueing and torqueing on some rod bolts to get the stretch, and calling the manufacturer to ask why. His question: "What lubrication did you use?" Duh, I didn't use any. But that was on the fail safe side.

What is it Pauter says about reusing rod bolts when you have the initial lengths? OK if no more than 0.0015 inch permanent elongation? Given how engineers build safety margins into things, I suspect that you should not lose sleep if one of yours measured out at 0.0016, but then the question is where do you stop?
Old 10-29-2016, 03:52 PM
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It may help to look in a little more detail of how metals typically deform when subjected to the tensile forces produced when a bolt or a stud is tightened. It may also help to consider some basic definitions.



Tensile test curves are normally produced in terms of Engineering Stress (s) and Engineering Strain (e) as opposed to the more detailed True Stress (Ơ) and True Stain (Ɛ). The differences in these values is subtle and not really relevant to this discussion so can be ignored but there are many detailed explanations that are easy to find.

Engineering stress is found by dividing the load applied(P) to a test piece by its cross-sectional area. (A). Any changes in cross-sectional area that occur during testing are disregarded.

s = P/A

Engineering strain is a measure of deformation that occurs during testing relative to the original size of the test piece.

e = (Ao - Af )/Ao

or e = (Lf - Lo )/Lo

Where A = Area and l = length

Another useful definition is that of Young’s Modulus (E) which is the slope of the elastic portion of the Stress/Strain Curve and is commonly known as Young’s Modulus.

Fasteners in the elastic region typically obey Hooke’s Law – which is to say that they are linear elastic – by contrast some materials such as rubber behave in a non-linear elastic manner.

The vast majority of fasteners are designed to be used within the linear portion of the stress/strain curve and as such will return to zero strain once unloaded.

A Grade 12.9 fastener is an example and the maximum quoted torque would typically result in a preload that is 70% of the yield stress of the material used for its manufacture.

The Yield Point of the material is shown on the above curve at ①.

(There has and is always debate about the definition of a ‘yield point’. Some steel exhibit discontinuous yield behaviour but heat treated steels used for high strength fasteners tend not to behave in this manner. Determining ‘yield point’ can be difficult and the industry standard is to use the stress at a 0.2% strain offset as this is a measurable and repeatable value shown as ①A.

If a bolt is loaded beyond its Yield point to say position ② then plastic deformation has occurred.

When the bolt is unloaded it will retain the plastic strain but the elastic deformation will still be recovered.

When the bolt is loaded again it will not yield again until it reaches ②.

Once the bolt reaches ③ it will no longer support load and the neck forms and the load carrying capacity reduces until failure.

So where does that take us:

Quote:
Originally Posted by Trackrash View Post
OK. So to clarify, one could;

Measure the length of the bolt.

Torque the bolt, again measure the length of the bolt.
No real need as this only tells us the estimated preload assuming the bolt is still elastic.


Quote:
Originally Posted by Trackrash View Post
OK. So to clarify, one could;
Release torque, again measure the length of the bolt. This measurement will confirm the bolt is still operating within its elastic range.?
Yes you can assume if it retains to the original length it will still be elastic.

Quote:
Originally Posted by Trackrash View Post
OK. So to clarify, one could;

What if;

Measure every bolt.

Assemble rods and crank and torque all twelve rod bolts.

Measure every bolt.

Assume for this example that 11 of the bolts stretched .009". One bolt stretched to .012".
Can it be safely assumed we have 11 good and one bad bolt?
If this happens it is unlikely that you would arrive at the set torque as the only real way this could happen is if you had stretched the bolt to ③ and the torque would be falling .

The method I suggested for checking bolts does assume that even if the bolts deformed permanently during original tightening that they had been working between points ② and ③ and that providing they were still elastic they were safe to use.

I suggested this method to provide confidence in re-using the bolts not because I am worried about them failing but to try to remove the concerns abut 'malleable' bolts.

Con Rod Bolts are always preloaded to stress levels greater that the alternating stresses seen in service and fatigue is never an issue.

If fatigue loading did occur we would see con rod bolt failure on a regular basis.

Quote:
Originally Posted by Walt Fricke View Post
Well, when you are measuring rod bolt stretch you don't use torque as your stopping point - you use stretch. Once stretched to spec, you have applied the required clamping force to the joint. It appears it is good practice to note the torque at which you achieved the stretch, because if you got the stretch on one bolt at a whole lot less torque, you would suspect that was a bad bolt. Unless you had wildly varying lubrication between bolts or some such other variable. I'll never forget torqueing and torqueing on some rod bolts to get the stretch, and calling the manufacturer to ask why. His question: "What lubrication did you use?" Duh, I didn't use any. But that was on the fail safe side.

What is it Pauter says about reusing rod bolts when you have the initial lengths? OK if no more than 0.0015 inch permanent elongation? Given how engineers build safety margins into things, I suspect that you should not lose sleep if one of yours measured out at 0.0016, but then the question is where do you stop?
The suggestion I made was to use a stretch gauge to check a standard 911 Rod Bolt to ensure that it was still elastic at the preloads developed during the torque tightening recommended by Porsche.

If you have the correct stretch figures then tightening to stretch is by far the best method but if you don’t have any manufacturers information then it can be an issue as you may not know where you are on the stress/strain curve of the material.

If an 'elastic' bolt will not develop the correct stretch for a given torque then it must have exceeded its yield point and have been incorrectly heat treated and the manufacturer’s quality control must be relatively poor.

I would have to say that if I bought any fasteners that suffered from this type of inconsistency I would think long and hard about using them again.

A plastic deformation of 0.0015” on a 2” long fastener isn’t much to worry about in terms of the fastener but it does suggest that the bolt has potentially been overtightened. If the bolt was designed to be elastic then stretching it permanently by around 1.5 thou will be an increase in preload of around 25-30%.

This is more likely to cause an issue with the connecting rod and we do need to consider the overall component performance.

Last edited by chris_seven; 10-30-2016 at 04:57 AM..
Old 10-30-2016, 04:32 AM
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Very enlightening info Chris. I never understood why it was suggested to always replace the rod bolts. It seemed to go against logic.

Thanks for the education.
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Old 11-02-2016, 08:04 PM
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