ARP head studs
 

I've got to the part in my 3.5 rebuild where it's time to fit the head studs.

I have bought ARP ones (nice box) and looking on this site there seems to be a lot of contradicting information as to how to fit them.

Do I glue them in with Loctite like the originals ?

These studs have a "nose" on the end, what is the installed height ?

I asked ARP these questions and they said look at the instructions on the back of the box,

what instructions:confused: :confused: :confused:

I was told DO NOT locktite the ARP headstuds in.... the tech guy at ARP advised to use the same moly lube that came with the studs that you use on the top of the studs, washers, and nuts. So, put the lube on the threads that go into the case as well. I did this on my watercooled VW and have had no problems. When I was putting my 930 motor back together, I called ARP, and they advised the same for both sides of the studs. Make sure that all the studs are inserted into the case the same length. Hope this helps.... I would call ARP tech reps just to confirm..... for your own reassurance... Brad

bty, the instructions should be on the cardboard outer sleeve of the box...

Re: ARP head studs
 

What ever you do, don't bottom them out, screw them all the way in and then backup two turns., Candy.

I have been reading about ARP head studs coming loose.
I think Steve commented on this problem.

I used Supertec head studs on my 375 hp 3.5 Turbo and they have stayed in place for over 18K without retorquing.

They (Sup) are installed using blue Loctite in the case and anti seize on the nut. They are designed differently but I wonder if loctite may cure the ARP loosening problem?

The factory studs (latest divalar) come with a locking compound already on the stud.,Candy.

I can't imagine why there would be a problem using locktite to hold these studs in. Also can't imagine why you'd put assembly lube on the end that goes into the case. There should be a measured depth to install these to. You could do a trial assembly of one cylinder and head to see how deep to install them and get the right amount of thread for the nuts. Just be sure that they aren't bottomed out like Candy says.

-Andy

call ARP...thats what the tech told me.... I questioned it as well, but they are the ones who made the item, so they should know...

Hi Jim:

A clarification is needed. :)

The ARP studs never loosened from the case as long as they were installed properly. The head NUTS were the ones that loosened up and in a few cases; backed up almost all the way off the threads.

One well known engine builder suggested to me that I failed to torque them properly and I told that fine gentleman that not only di I know hoe to use these tools, but our torque wrenches are checked & recalibrated at least once a year. We use Snap-On split-beam models as well as the new electronic ones...:) :) :) :)

Hope this helps,

Hi Steve
I believe proper installation of ARP head studs is what this thread is about.
It was not my intention to put words in your mouth.
I was just trying to add something of value to the conversation. Referencing an expert incorrectly was not what I set out to do.
What fool questioned your expertise? I for one believe that you have the required knowledge to operate a torque wrench properly. :)

Don't you think that anti seize on any tread could promote loosening?

Do you use Loctite on the case end?

Why do you think the ARP studs are coming loose?

Hi Jim:

No worries, mate. :)

It would be inappropriate to name the party that suggested my inability to use a torque wrench on a public forum, even though the other party did just that,...:)

I have never used nor needed anti-seize on head studs, but I do use Loctite to anchor the case ends. Since it releases very easily with heat, its not a problem at all. I use anti-seize (copper or nickel based) on fasteners living in harsh environments that will be disassembled from time to time. Exhaust systems are a perfect example as well as suspension hardware that anchor into aluminum alloys.

Its my view that ARP head studs, while an excellent metallurgical product, do not accurately match the expansion rate of these engines very well and the head nuts loosen over time, especially with engines that operate at higher temps (930's, race motors, etc).

I use steel studs on the little engines and 993TT/RSR Dilavars on everything else. Been doing this since 1993 with no issues whatsoever. :)

Steve, What defines a "little engine"?

Thank you!

Well I got through to ARP's tech' department and this is their official installation procedure:-

Hand tighten them in,
Use the supplied lube and torque to 38 ft/lb,
You can use Loctite if you want but torque 'em' down before the Loctite sets.

What about installed height ?
No answer on this one.

I was not over impressed by the quality of the advice, either they answer these questions every hour or they make it up as they go along.

So I'm going to hand tighten them in, back them out to the correct length, use Loctite, torque 'em' down.

and while I'm on here I did my own machining for twin plugging my heads, all worked out really well, didn't need to use any messy wax in the fins, I have a "patented" two bits of wood approach. If anyone is thinking of doing this I can advise and put some pics up.

Cheers Pete

and while I'm on here I did my own machining for twin plugging my heads, all worked out really well, didn't need to use any messy wax in the fins, I have a "patented" two bits of wood approach. If anyone is thinking of doing this I can advise and put some pics up.


Sure like to see that.

well as your interested.

I thought the sticking wax in the fins a really messy approach as I had just paid £90 to have the whole lot bead blasted. If this pic uploads OK, I made a clamp out of two bits of packing case backed with 1" x 1" steel box. Worked great, no vibration no broken fins.
http://forums.pelicanparts.com/uploa...1177537891.jpg http://forums.pelicanparts.com/uploa...1177537920.jpg http://forums.pelicanparts.com/uploa...1177537946.jpg

Raceware head studs are also used without Loctite on the case ends.
-Chris

I don't use ARP head studs but if they use 12 point nut instead of allen nuts (stock Porsche) then installed hieght has no meaning.
38 lbs ? That seems like a huge number. Not my product but I would have to ask how they came up with that number.
I would only use that kind of torque on a 800 hp 1/4 mile motor.

Anything with an 86mm bore and under,....:)

I used ARP studs on my rebuild. I carefully measured the stud height to arrive at a height where the 12 point nut was in the middle of the available thread. I found that the hieght was correct when measuring to the top of the thread, before the taper on the rounded top. I still have less than 10,000 miles on my rebuild - but I plan on checking my head nut torque during regular valve adjustments.

Just to keep the record straight. I'm not sure if I'm the Steve referred to, but I did recently post that maybe my ARP head studs were backing out. I now have all the studs out, and can say that most of them were firmly in place. None seemed to back out or be loose. Two were pulled -both on No. 1 cylinder exhaust & intake toward the front of the engine.

My memory is that the height is 135mm to the top of the threads. That's what they were when I removed them. 38 ft-lbs is the same torque value I got from ARP, too. I also asked them to send me the installation sheet for that kit. ARP moly lube on the top; nothing required on the bottom - but if a sealant is used ... torque before it sets.

By the way, the hardware looks perfect after 30K miles and 5 years.

Based on what Steve said, maybe I should go back to the new style dilavar. More choices . . .

I used blue locktite at the case and ARP lube at the top. Installed height of 135mm to the top of the threads also. Using the ARP washers the threads should be just at the top of the 12 point nut when you do final torque. I used factory torque specs on mine since I have a Mag case. I will retorque to factory specs at each valve adjustment.

It's OK to check that the nuts aren't loose but you don't want to be retorquing them. (Please, someone correct me if I'm wrong.)

People get hung up on the accuracy of the torque wrench but what they really should be worrying about is duplicating the conditions for which the torque spec was specified. I've read that as much as 80% of the torque on a fastener is due to friction.

With that in mind, lets take the case of head stud nuts. When assembed the nut was antisiezed on a (hopefully) smooth washer. A year later that nut, stud and washer are rusty and have a totally different coefficient of friction.

-Chris

Steve: This is a very timely discussion for me. I put ARP studs in about 5 years ago. They still look great - perfect threads. I pulled two studs on No. 1. All others look fine, though I intend to timesert the whole case to be sure.

I see that you have had great success with the 993 Dilavars, so I certainly understand your commitment to them. If I didn't already have the expensive little ARPs, I'd probably jump at buying the 993 studs. But, I am wondering, though, what is your opinion based on that the ARPs "do not accurately match the expansion rates of these engines?" Would my pulled studs be an example? Have you seen other problems? I still haven't found anyone who will say that they've seen pulled studs on a 964. Have you? Could the ARP be my problem?

Thanks!

I you are certain that no tread damaged was caused during the removal of the original studs, ARPs torqued to 38 lb on a street engine would be my guess.
We have never seen studs pulling in an aluminum case unless tremendous horse power out puts were achieved.

Steve:

Like Henry, I've never seen a pulled stud on an aluminum-cased engine unless they were improperly installed. In the case of high HP Turbocharged race motors like 935's, other things happen first such as head lifting. :)

The only issues I've seen to date with ARP are the occasional loose head nuts but not a pulled stud. Either they were improperly installed or this is the first instance of pulled studs from expansion-related stresses.

I'm not one to speculate but it seems that if this was due to stresses, several of these would have pulled their threads out,......OTOH, the combination of too much torque and maybe a loose one might have been the culprit. At this juncture, any accurate forensics will be almost impossible to do.

If it were my engine, I would sell those ARP ones and install the 993TT Dilavars.

My .02…this certainly isn’t directed at anyone, I ‘compete’ with no one on this forum.

Using a torque wrench is just guesswork, it gives a pre determined number to shoot for but doesn’t come close (unless you just get lucky) to the tension elastic limit which will yield the fastener’s maximum inherent strength. There are computerized ‘torque wrenches’ that will signal you of this condition but are not accurate enough (despite their boasts) to be used for much other then a fail safe…i.e. bringing the fastener to a particular torque number and warning you of a possible fastener problem, burr, thread degradation etc. I use one of these for that purpose, to slowly bring a fastener towards the correct stretch without going over…expensive at well over $10,000 but mandatory in my opinion. For non-critical fasteners this wrench is enough, but I would never dream of stopping there for cylinder heads and other critical fastening. For that I use an extensometer, I personally use a BoltMike III, great tool, but also over $15,000. A few engine builds using one of these and you will quickly realize just how inexact a ‘torque wrench’ is.

Meticulous engine building isn’t cheap, that is for certain. It is science as much as art.

Why should you screw the studs all the way in and then back them out 2 turns?

Lube on studs
 

Hi all, I am somewhat confused here.
Tomorrow, I am going to rebuild the heads and cam boxes etc on to my std 3.0 Sc engine.
I have bought a full set of steel head studs....You mention not to use the lube on head nuts on your type of studs. Is this true of the steel studs, or should I lube the washers and threads as suggested in waynes book.

Thamks

The subject of expansion is regularly discussed and I would just like to rpeat the numbers:

Typical Aluminium Silicon Alloy: 20ppm/degC

Typical Cast Iron: 9.5ppm/degC

Typical Steel Stud (8740 or similar) : 12ppm/degC

Dilavar Stud: 18ppm/degC

ARP Inconel 718 Stud: 13ppm/degC

17-4PH Martensitic Stainless Steel: 11 ppm/degC

Clearly the preload in the studs will increase as the cylinder expands and I am not sure why this would cause the nut to loosen.

If the studs were to yield then there could be an issue but this is unlikely.

I come back to my argument that excessive preload in the studs will cause the Alusil to suffer from local stress relaxation which will cause this problem and reduce the clamping force.

Alusil alloy are known to exhibit this type of behaviour even at modest temperatures.

I think the message is to torque them carefully, glue them in well with Green Loctite.

If you are going to use either Inconel or 17-4PH I would use a thread lube.

Silver Goop made by Swagelock is good and prevents any galling during tightening and has good anti-sieze.

As Dilavar is an Austenitic Material it is also one of the stainless steel family and can have a tendancy to gall unless they have a surface treatment to prevent this.

Having never used Dilavar I don't know if the threads are coated.

To minimize imparting stress into the engine case.

If the engine is assembled with the studs bottomed out and If the stud for whatever reason ever gets hotter than the engine case, then the stud will potentially elongate (thermal expansion) and then push against the case, impart stresses into the engine case.

There are at least three states,
1. start-up transition (warm up)
2. steady state - run (normal operating temperature)
3. shut-down transition (cool down)

Yeah, I know it's over-simplified as what exactly constitutes steady state, I'm sure the surface temp for the cylinder and for the studs is all over the place, but, I believe that the loosening has to happen on a cool down, where the stud is hotter than the cylinder. What do you think?

If the stud does hold more heat than the cylinder, which I think is unlikely, then surely all types of stud would be affected regardless of their material. In this situation Dilavar would be the most likely to cause a problem as it will be longer than all of the other materials during the cool down transition.

The heating and cooling cycles do change the stress/strain conditions in both the studs and the cases and the focus of problems is always blamed on stud quality.

At the temperatures involved it is extremely unlikely that there are any creep mechansims operating in any of the stud/nut materials we are concerned with.

Inconel 718 and Dilavar (similar to A286) are materials that are commonly used at elevated temperatures and both have excellent stress/rupture characteristics.

17-4PH is not quite as resistant to creep as the the above materials but can still be used succesfully at around 900 degF.

Even the most basic stud material 8740 has more than adequate properties to show that creep is an unlikely mechanism at the temperatures being reached in a 911 motor.

Well it IS a complicated device. Who could blame you? All that turning and looking at numbers.. Makes the head spin. :rolleyes:

*cough, 5yr old thread revival... *cough

Metal expands when heated and fasteners hold best when drawing against one side of the thread. Imagination should be able to take it from here.

I think if you bottom the stud into the hole when they expand they will tend to push the threads out of the case and cause a serious failure. The really do need a clearance.:)

Old thread and for what it's worth I called ARP customer tech service and asked why they mention not useing loctite on their head studs when installing them in the case in the instructions if it might not be a permanent installation.

They said using loctite when doing a permanent installation or race motor installation is fine and good but if the studs are ever removed in the future using a stud remover tool that has the 3 rollers inside that clamp the threads as you turn it they could squeeze them too hard and damage them if the studs are glued in with loctite and require a lot of torque to remove. That could make them nonreusable.
That's the only reason.

If double nutting the threads to remove the studs gets them loose that shouldn't damage the threads.

I used red loctite when installing ARP head studs in my aluminum case. It gives me more confidence in them staying put.

MAP gas in the yellow bottle works good for heating the case around the stud to soften the loctite if you ever need to remove them.

In response to what JFairman found out from ARP customer tech service:

They said using loctite when doing a permanent installation or race motor installation is fine and good but if the studs are ever removed in the future using a stud remover tool that has the 3 rollers inside that clamp the threads as you turn it they could squeeze them too hard and damage them if the studs are glued in with loctite and require a lot of torque to remove. That could make them nonreusable.
That's the only reason.

There are tools for removing studs that don't damage the threads. I have a couple of them. I believe they are called "collet style" stud removers. The kind I have aren't available anymore but Snap on makes some.

Double nutting can also damage/distort the threads if you tighten them too much so you need to be careful.