Another ARP rodbolt question..

[Geronimo '74]

Hi,

I'm having my engine (3.2 ROW) rebuilt by a mechanic who is very familiar with aircooled Porsche engines.
I bought ARP rodbolts for him to use instead of the stock ones.
He has the installation instruction from the ARP website.
He has never used ARP bolts before so the fastening procedure was new to him but since it is not rocket science there should be no problem.

He installed the rods on the crank using the stretch method. All went well, no issues so far.
He then went on, put the crank in the case and closed it up.

The next morning he rechecked the bolts with a torque wrench.
ARP recommends 40 ft lbs when using the torque method, so that is the values he set on his wrench.
9 bolts immediately showed the correct tightness but three of them were not yet at the right torque.
For these three bolts he could turn the wrench a quarter to a half turn before reaching the speciefied torque.

He now thinks that those three bolts might have overstretched and does not trust them anymore.

He suggests removing the ARP bolts and using stock bolts instead, tighten them with a torque wrench and be done with it.

The case is closed up and I'd prefer to keep it closed instead of opening it all up again.

Are his concerns justified or can we still use the ARP bolts? (which I would prefer)

Any input, info?
Thanks guys.

PS, engine is to be a hot street engine, not an all out race monster.

[Walt Fricke]

You are in a bind, aren't you.

I'd take the case apart (not that big a deal at the short block stage), and remove the suspect bolts.

If done properly, he recorded the pre-stretch lengths of all the bolts. And the stretched length.

First off, he can check to see if the stretch changed. If somehow the rods weren't fully closed on their alignment bushings, perhaps they could have crept closed, causing the apparent looseness. And the stretch should have lessened by about that quarter/half turn.

If that does not tell you anything, I'd loosen the suspect bolts fully and measure bolt length. I assume he recorded the pre-stretch lengths of all the bolts. If the bolts returned to their original length, or at least had a residual stretch within what ARP says is acceptable, you can just reuse them.

If they are permanently elongated beyond spec, toss them and get new ones. It is tricky to get just a few bolts instead of a whole set, but asking around on Pelican may produce someone who bought a set to replace a few, and will sell you three or four.

The rod bolts are the Achilles heel of the 3.2 because of their lesser diameter than their predecessors. Which is why it is attractive to use super strength aftermarket bolts. However, if the car is not raced or otherwise subjected to abnormal stresses from constant wide open throttle and high RPMs, the stock bolts seem to do fine.

Me, I'd like to have the extra strength. Especially if "hot" means you have done things to the motor to increase its power.

[BoxxerSix]

Agreed. Buy a new set of bolts, record free lengths, then stretch to appropriate lengths. New set of bolts is pennies compared to a blow engine when rods let go.

Also why doweled rod caps should be lightly seated with a small rubber mallet after just hand tigtening the rod nuts, to ensure the cap is seated sqaurely and that you're not relying on the rod bolt to pull the cap in if one of the dowels is pinched.

[BURN-BROS]

I had the same problem a few weeks ago with a set of 9mm ARP bolts. I use stretch and torque to verify consistency. I had two bolts that went to specified stretch @32 ft/lbs instead of a closer 38/40 ft/lbs. I called ARP and talked with an engineer who got me replacement bolts for the ones that did not pass.

Do not throw away the whole set as the rest are good.

You should give ARP the stretch and the torque readings for the offending bolts.

Do not let the sales department tell you to "only use stretch". They tried that with me.

ARP will supply you with replacement bolts.

Remember to keep the nuts as ARP will not supply them.

[KTL]

The rods here are stock rods, yes? If so, there are no dowel sleeves in the rods. The bolts must align the cap and rod via the bolt shank

That said, I recently removed my Pauter rods and they do have dowel sleeves. I definitely agree that given the tight fit of the dowel, you should tap them with a soft mallet to get the cap seated on the rod as much as possible.

Anybody doing a search in the future about the dowel fit or removal....... The recommended way to separate the cap from the rod is to loosen the bolts incrementally to relieve the load on the cap. With the bolts fully loosened ~1/4 in. you can tap on the bolt head with your soft mallet and that will press the cap off. Don't do the tug and pull method like a dufus- i.e. ME.

[Geronimo '74]

Thanks for the input.
Looks like I'll be looking for a new set of ARP bolts and have the mechanic open up the case again.

[haycait911]

if using the torque method on ARP bolts, there's a specific procedure. as I recall involves pre-running the nuts to burnish the mating surfaces and using their special lube.

I didn't think it makes sense to use one method to tighten ( stretch ) then checking by torque without following the proper torquing procedure.

[Geronimo '74]

Originally Posted by haycait911

I didn't think it makes sense to use one method to tighten ( stretch ) then checking by torque without following the proper torquing procedure.

Good point! And in retrospect it sure makes sense...

I'm sticking with ARP bolts because the risk just is not worth it.
But it would sure be nice if there was one, clear definitive way of tightening them.
Some use the stretch method, some torque them, some use a combination of the two. I'm not that good of a mechanic, I need simple, idiotproof instructions...

Let's say, I put the rods on the crank using the stretch method.

-do I need the lube provided by ARP? (I would say not)

-When properly fastened and stretched, do I need to recheck later on? How do I best check?

- Is it possible that after checking the bolts need some extra tightening/stretching? Can I stretch them more, knowing the they were at the desired length at first?

-Do I need to verifiy torque values if I installed them using the stretch method?
What if the specified torque is not reached but they are stretched to spec? Is optimal clamping force reached or do I need to tighten more??

My mechanic failed to note down the individual pre stretch lengths so I have no way of knowing which ones are reusable or not. So I'll be buying a complete new set.
They are not cheap so I want to get it absolutely right this time.

[Walt Fricke]

Well, the procedures I recall are meant to burnish the threads, which I believe is going to allow the final torque number to more accurately reflect the needed stretch in the bol, and to stretch all the bolts more closely to the same length.

But the "torque after stretching" approach is just a safety check. My experience has been that I needed quite a lot more torque than the specified amount to get the needed stretch. Which is fine, because it is stretch which counts, not torque. If I got any movement at the maker's torque value after stretching but without burnishing I'd really think something was wrong.

In fact, I have usually just torqued, measured, upped torque and measured again, etc. until the various bolts were at the right stretch. Usually starting with or close to the maker's recommended torque.

With some suitable tool I suppose you could tighten a bolt while actually measuring stretch, like by using a box end wrench? Then you might want the peace of mind check with the torque wrench.

Because having a bad bolt would be a real downer. And it appears from the experience Aaron has shared that is possible even from a very good manufacturer.

[Walt Fricke]

This is not all that complicated. What you want is to press or clamp the two parts of the rod together with a certain amount of force. That force needs to be greater than the forces trying to pull them apart will be when the motor is running. This can be calculated, and the rod maker has done so, as has the bolt maker. If the bolts are good for it, having lots more clamping than needed can be a good thing, in case inadvertently the forces are larger than they should be, as in a missed shift. Nice to have safety margins.

Stretching (or, if you will, tensioning) a bolt of a certain diameter and quality of steel a certain amount will produce that tension or clamping force. It can help to think of a bolt as a really strong spring or rubber band. More stretch, more pull trying to get back to the relaxed state.

You can determine most accurately the stretch with a stretch gauge. You can do a good job of approximating that stretch with the angle method, because the pitch of the threads equates directly to stretch. And you can torque, because the engineers have determined, experimentally, what torque will produce the needed stretch. Because it has the most variables (friction coefficients here and there), torquing is apt to be the least exact method. And calls for the most technique.

The fact is that the ARP bolts have so much higher tensile strength (which equates to clamping force per unit of stretch) than the stock bolts that the ARP specified torque methods are going to produce adequate clamping force. So if you are just using torque, you are safe just following their instructions. To the letter, of course.

Shame on the mechanic for not recording things. One of the virtues of these super bolts is that in many cases you can reuse them. The stretch/torques specified are intended to keep the bolts in their elastic range, which means that when relaxed they get shorter again, back to where they were at first, or awfully close (say within half a thousandth of an inch). You won't know that if you don't write it down. Takes a bit more time than just zeroing the gauge each time, but very useful down the road.

I see no reason to fiddle with retorquing rod bolts once you are sure things are right. . Makes sense with CVs, because there can be things which can squish more (those gaskets, the soft steel of the boot holder). And head bolts squish copper gaskets and such. But not rod bolts.


I admit I hadn't considered the issue of having bad bolts from ARP (or Raceware, another maker of super bolts). That's whre Aaron's experience as an engine builder comes in - does this a lot more, usea a lot more bolts, etc. Which I suspect is why he has taken to a safety check.

Someone may point out a flaw in this, but I think that using a torque wrench to develop the stretch ought to do the same thing - weed out a bad bolt which gets to the proper stretch without first achieving at least the specified torque.

What you should see with these super bolts is more than that torque to get the stretch. When I have neglected to lubricate things, I've had to use a huge amount of torque to get the stretch needed. Scary. I called the manufacturer. He said I probably had screwed up the lubrication (as in none). Didn't really matter - I wasn't going to torque the bolt apart, and eventually the stretch crept up to where it needed to be.

[Geronimo '74]

Thanks Walt,

Tightening using a torque wrench is indeed a good way to see if all bolts reach the specified stretch/tension and at the same time reach or exceed the specified torque. (when using the ARP lube.)
Without the lube, almost certainly higher torque values will be reached which makes loads of sense...

If a bolt reaches the desired stretch before the specified torque is reached, would that bolt be faulty? (I would say it is)

Can one safely tighten the bolts using the stretch method without using the APR lube?
Dumb question maybe because I reckon you can.

If all bolts are tightened with the stretch method and allowed to sit for a while. Can it be that after a while some bolts will have shrunk again if even for a very little amount? And can you retighten/restretch them to the specified lengths?

[304065]

Originally Posted by Geronimo '74

Thanks Walt,

Tightening using a torque wrench is indeed a good way to see if all bolts reach the specified stretch/tension and at the same time reach or exceed the specified torque. (when using the ARP lube.)
Without the lube, almost certainly higher torque values will be reached which makes loads of sense...

If a bolt reaches the desired stretch before the specified torque is reached, would that bolt be faulty? (I would say it is)

Can one safely tighten the bolts using the stretch method without using the APR lube?
Dumb question maybe because I reckon you can.

If all bolts are tightened with the stretch method and allowed to sit for a while. Can it be that after a while some bolts will have shrunk again if even for a very little amount? And can you retighten/restretch them to the specified lengths?

I don't know that I would go throwing bolts in the garbage because they reach stretch at a lower torque unless that torque is WAY lower.

Remember, the use of the stretch method is intended to eliminate the variability that comes with using the torque method as an approximation of the correct installed preload.

Factors that affect it are:

1) Burnishing of the threads. ARP tells you to install and torque up your set of bolts three times, this knocks down the bumps on the threads of bolt and nut and smooths out the surface following the machining process. It has the effect of decreasing the level of friction. Friction is what causes the torque wrench to click-- friction between the surface of the nut and the face of the rod's cap, and friction between the threads of the nut and bolt. When the preload on the fastener rises to the point that the friction can't be overcome by the force you are exerting with the torque wrench, "somethin's gotta give" and what gives is the beam in the torque wrench: <>

2) Lubricant on the threads. ARP specifies their own blend of Moly lubricant so they can better control the process. No repeatability if one customer uses 3 in 1 oil and another uses extra virgin olive oil.

3) Corrosion on the threads. Yes, corrosion.

4) Temperature of the room in which the operation is being performed. Yes, this makes a difference. Measuring labs are always held at 60F for this reason-- the repeatability changes if one guy is in Tampa and another in Upstate New York (where I assembled my own ARP bolts in 40F temperature)

5) Calibration of the torque wrench. Who sends theirs out to be calibrated? I have two Stahlwille wrenches, the beam-clicker type, and I've never sent them out. One of mine was brand new when it was used for critical assembly, but four years later, its accuracy could certainly be checked. Torque wrenches that we can afford are usually good to about 4%.

Of these factors, ARP considers the lubricant to be the biggie:




So these are all things that make the stretch method preferred.

I do think it's a good idea to measure the torque at which stretch is achieved as a backup. Here's what I would do.

1. Unpack all the rod bolts and measure the length with a micrometer. I would use a pointed tip on one end that fits into the dimple at the end of the bolt. I wouldn't use a ball tip because the ball doesn't quite fit in there. Using the flat tip would make me wonder where to put it.

2. Find some way of marking the bolts so you know which is which. Try not to create stress risers by hitting them with a punch. I am still looking for a good way to do this.

3. Perform the "burnishing procedure" as specified by ARP- torque them up three times and release. They don't tell you to do this anymore in the instructions.

4. Measure them again. Note any deviation from length.

5. Stretch them to final preload as set forth in the instructions and note the torque at which this is achieved.

Look, ARP bolts are not "torque-to-yield" fasteners, so you can take them apart and measure the final length and compare it to your starting measurements. ARP says that permanent stretch in excess of 0.0005" (.0127mm) means the fastener has reached the yield point and has permanently deformed. You can also tell because the diameter of the bolt will neck down.

So if you have a bolt that goes to final stretch at say, 38 foot pounds, by all means check it but make sure the other components of your technique are perfect before junking it. When in doubt, measure first.

[BURN-BROS]

The lube is important because they give you a torque spec if you are not using stretch.

You can reuse the bolts that go to "stretch" because they are at 80% yield so no permanent stretch has occurred. However If you do not know how they were initially installed then it would be prudent to replace all.

I discovered the problem when at 36 ft/lbs I was @ .015 stretch and they felt different than the ones that were reading .009 stretch@ 26ft/lbs.

Since this is another set of 9mm rod bolts with weird readings ARP may have a poorly heat treated batch coming in at the moment.


Engineers try to stay away from torque as it has too much variance, but doing both has served me well.

Also, I am not throwing rod bolts out because they do not reach the torque spec. I am looking for consistency and using torque as reference.

Edit;

I have a friend in the business that ruined a set of CARR bolts because they used ARP lube when they specified moly. All went past stretch prior to reaching the specified torque.

[Flieger]

Stretch is all that matters (provided the area of the bolts is to spec).

I would instal them to the specified stretch first. Then check with the torque wrench. If any are lower, I would think about removing them if they are significantly lower and make sure that the bolt is within the hyteresis spec: if the bolt returns to its original length + or - 0.001mm (or whatever the spec is) then the bolt has not yielded and it is fine to re-install the bolt to the specified stretch and be happy. These bolts are designed to have a higher elastic region and to not be plasticly deformed.

The torque specs they provide certainly will include a safety factor to account for improper torquing procedure as far as lubrication and burnishing. They will want you on the high end of the elastic region to be safe. Therefore, if the bolt reaches stretch before the specified torque I would not see that as unusual. They can allow a smaller safety factor in the stretch method because it is so much more accurate at gaging the actual clamping force.

[jwasbury]

Originally Posted by Walt Fricke

My experience has been that I needed quite a lot more torque than the specified amount to get the needed stretch. Which is fine, because it is stretch which counts, not torque.

This was also my experience using the ARP rod bolts in my build. I was concerned, but I did a search here on pelican and found that the general consensus was that the proper stretch was achieved with more torque than is specified in ARP's instructions for the torque method.

[KTL]

More food for thought and others' experience with torquing ARP rod bolts. Some good comments on why the torque method is a wise double-check after stretch. Just have to wade your way thru the Carillo love fest.......

ARP Rod bolt won't torque!

[haycait911]

I'm just more comfortable with the torque method than the stretch. here's my version of the procedure.

- pre-run the nuts to full torque three times with ARP lube and on rods w/o bearings ( extra rods if possible )
- use a little ARP lube on the bolt shanks.
- install bolts, lube threads and nut seat face, install nuts finger tight ( they should go on easily with fingers)
- torque all to 20 ft/lbs
- torque all to 30 ft/lbs
- next day, or week, or whenever, torque all to 35 ft/lbs
- next day, or week, or whenever, torque all to final torque number less two ft/lbs
- next day, or week, or whenever, torque all to final torque number
- next day, or week, or whenever, re-torque all to final torque number.


I don't build engines very quickly so the above timeline works for me. my thinking is to allow the bolts to seat the caps well in case the bolts bound up in the rods a little in tightening.

note: my engines so far have been more of the low-rev type, up to 7k. except for one mis-shift that was more like 9k+.


.