ARP head stud torque for a Miata.
 

Searching yields wildly different answers. I do know some are really wrong.

Facts.
1) The factory head bolts specs are 56-60 ft-lbs.
2) ARP head studs have finer threads and the nut is lubricated with ARP Molly.
3) Using the same torque value as factory bolts will result in significantly more than factory clamping force due to the design of the studs.
4) As far as I can tell ARP studs are 11mm and 190,000 PSI tensile strength studs.
5) The box they come in recommends 71 ft-lbs for that size stud “to achive Optimum clamping preload (Clamping Force)
6) I have tightened them to the 10mm spec of 48 ft-lbs in the past and it has never resulted in a problem even at 300hp levels.
7) I have tightened them tighter based on internet info and destroyed a head with $2000 worth of port work on it by smashing the bosses and cracking it. I can’t remember what that torqe was but it wasn’t much more than 71 ft-lbs if any.

My guess is somewhere below factory torqe spec is what you wan’t with ARP hardware. My guess is they will still clamp harder than stock and you really don’t want to go with much more clamp than stock. So what is the spec? my guess is 48-50 ft-lbs. What is everybody else doing?

PS. I actually think the ARP head and main studs are solving a problem that simply doesn’t exist on a Miata but I have them anyway. About the only thing I think they could be doing is providing more consistent clamp force at each stud than stock.

Bob

Have you measured your used gaskets?
Turboford.org had dedicated threads discussing this with iron and alloy heads. The stock Ford 'bolt' specs were too high with studs (IIRC).
Way too much and you collapse the heads around the studs. Too little and, well, blown out h-gaskets as well.
Alloy heads on iron blocks can be a problem. Differing expansion rates can smash the gaskets around the studs/bolts. Even clamping is what is wanted. The head's RA is also a factor.

Measure your used h-gaskets around the studs and in-between. Need to keep records of the torque used also. The most even without failure, such as the fire-ring moving, is what we're after. Sorry I don't have any numbers for you, just suggestions.
BTW, I'm drunk-posting, so this may not even make sense to me in the morning... Editing 'cause I've had way too much, and it's getting hard to type, and I know i've left stuff out...

I purchased my studs from Flyin Miata, and they had a correction in the instructions to torque them in the 50 ft lb range.

I would agree that Miatas are not notorious head gasket blowers. I would never have a race motor without them however.

As far as clamping force, I was under the assumption that studs were supposed to clamp harder than stock, but to maintain the integrity of the block threads. Race motors have the head on and off frequently, and head studs make parts last longer.

I clamped mine to 65 ft*lbs and didn't have an issue, but I also wasn't pushing even 200 hp. When I pulled the head off, the gasket wasn't crushed oddly or anything and it hadn't leaked. Just my experience. But as you pointed out, the head studs don't do a whole lot on our closed deck blocks. Their main function is simply being reusable. On open deck blocks like Hondas, they are absolutely essential. On my old civic, I was getting head lift and popped a HG at 7 lbs. ARP studs torqued to 75 ft*lbs and never happened again. Thats also an open deck, alloy head and block.

Its been a long time, but I seem to recall the instructions stating 50ft/lb with the ARP lube, and 65 ft/lb with engine oil, but don't use engine oil if at all possible. Would probably be best to call ARP.

I've never seen those instructions in like 4 boxes of Miata head studs I have had for various engines I have put heads on. I do know that the generic 71 ft-lbs listed on the box for 11mm studs is dangerously close to destroying a Miata head by crushing and splitting the aluminum bosses in the head they clamp down on. Miata head studs are significantly oversize for the amount of clamp force needed.

Bob

Sounds about right. Strangely I have an old email from Bill at FM stating 71 ft-lbs but I swear I remember they told me 48 before as well. You can also find people claiming 85 by searching. So there is a tone of confusion on this.

I now know the torque level on a Miata needs to be much less than the capability of the stud.

Bob

Holly shit I torqued them to 80 ft/lb!!!! :noob:

71lb here, I'll go lighter next time..

Holy shit so 50ish is fine??

The workshop manual is 60 on stock bolts

youre lucky you did not crack your head.

Shit Im lucky it ran for so long then. Lol.

It doesn't make sense to me that a stud that by it's design (Finer thread on super hard high strength I quality steel threads and well lubricated) should produce significantly more clamp force at a given torque level should be torqued any higher than stock. and most likely should be less.

Miatas don’t suffer from heads not being torqed tight enough. I can't see any reason to more than double the clamp force at the risk of crushing the head.

http://www.flyinmiata.com/projects/c...ts.php?UID=789

Note the picture. Stock bolts at stock torque don’t even hardly leave a scratch mark on the bosses.

Bob

I am thinking the stock bolts are softer so they stretch more requiring a higher tq to ensure correct clamping force on the head/gasket whereas the arp studs are stronger resulting in less stretch therefore needing less tq to achieve the same clamping force on the head/gasket.

Well shit. This all would have been good to know 7 months ago. I cant remember what torque spec I used on mine but it was sure as hell more than 50. I did not use the lube the last time I assembled my engine, just engine oil.

Oh well, working fine with no cracks (that I know of) so far.

After much thought on this subject, I opted out of studs for my GTX engine build and after reading this i'm glad I did.

lol oh well i did my ARP studs like 5 months ago with the lube and at 65lbs

Reguardless of the strength of steel all steels have really really close to the same elastic modulus so unless they are a different diameter then they are the same stiffness as long as you stay below yield. And the fact is the head will yeald under the washers before the bolts will and I think this is true even with the factory bolts. The factory bolts will require a lot higher torqe to generate that much clamp force though and they might twist before they generate as much clamp.

Bob

Curious how you arived at the 65lb torque level? was it documented somwhere?

Bob

Way too much conjecture and guessing in this thread for me. I followed the instructions that came in the box and I've had no problems at all.

What did the directions in your box say? I've never seen any instructions for them. I've had 4 boxes of these things and they never came with any instructions for torque level on a Miata.

There is a chart on the back of the box that has generic recommended torque values for 3 different material strength fasteners based on fastener diameter. They don't even tell you what material strength the fasteners that comes in the box are.

Again I have never seen a documented torque value for ARP head studs on a Miata. Go searching on line and you find wildly varying answers that dont seem right.

Bob

The instructions that came with my ARP studs said to torque them to 65 ft-lbs with the ARP moly lube. I bought them from FM a long time ago and it came with a little pink instructions sheet.

Here it is:
http://www.ferdster.com/forum_attachments/arp_studs.jpg

--Ferdi

Ok I got it.

None of my boxes I got ever came with that sheet. Maybe mine were Chinese knock offs or something from Ebay but the box says made in the USA. The threads in the block are 11mmX1.5 not 7/16" but I just verified the nut end is indeed 7/16X20 didn’t realize that before.

The back of the box says 63 ft-lbs for a 7/16 size stud and 71 ft-lbs for an 11mm stud.

And I can verify using the 70 or 85 lb values in the [A] part also shown on your sheet will yield the aluminum head with heat cycles and 85 lbs will likely turn your head into a paper weight. 65 Is probably more than necessary but OK I guess and it wouldn’t surprise me if it produced nearly double the stock clamp force> ~15,000 lbs of force per stud by there chart and the area under the washers is pretty small to apply that much force on aluminum especially when it heats up and expands more than the bolt does further increasing the clamp. I can also varify that 48 to 50 ft-lbs has no issues holding more than 300 hp.

Bob

I am not in any way calling you a liar but I'd like to see pics if you have any/still have the damaged head. This thread is a good one!

The lower torque (48, IIRC) is what the original engineer at ARP came up with when we worked with them to build a correct Miata stud kit that was an exact fit. He was basing it on stud diameter, head thickness and OE torque values. That guy is gone now and nobody at ARP since then has ever agreed with the low number. But we have used it for a long time without issues and the original guy seemed to spend the time to study the application. YMMV. ARP is pretty funny sometimes, they'll send a box where none of the nuts are threaded or sometimes the studs. Seems to only happen when we ship overseas...

I suspect the original guy was right and actually studied the application. I would about bet that 48 ends up with just around ~10% more clamp force than the stock parts at the OE torqe specs.

Bob

I will be torquing mine to 48-50ft/lbs after reading this thread. I'm glad the question was asked otherwise I would have followed the 85ft/lb direction.

I was questioning this as well as I noticed the difference between OEM and ARP torque values. I meant to retorque them as ppl told me I should go w/ ARP's specs (which I have on the box somewhere) but never got around to it.

Are the ARPs re-usable? Say since I torqued them down already and have gone through numerous heat cycles... I would like to loosen them, and start over to re-torque (especially since I don't remember what I tq'd them to)... would this be okay? Stock 1.6L... I threw on the ARPs "just cause."

Yes ARP studs are re-useable. I would say that is one of the reasons people would choose ARP over a stock bolt.

When I presented this question to the guys at ARP they told me:

You have to check the stud with a micrometer (clamp it down on the non-threaded part and run it down the length of the stud) to ensure it didn't stretch and inspect it at the base of the threads (where they start on each end) visually. Those are the places that will stretch and generally they don't unless there is a mechanical failure (disconnected piston hits the head, blown head gasket).

They are reusable because the studs or even the OE bolts for that matter don’t get anywhere near yield in the Miata application. But I would not loosen them if they are already torque unless you started with a fresh head gasket as well. Reducing clamp on the head gasket once it has been clamped to a certain level would be bad.

I suspect what happens if they are over torqed is the head starts to yield due to contact forces under the washers first. And that is another thing. ARP supply smaller OD hardened washers than OE so they will actually yield the head at a lower clamp force than OE as the contact pressure under the washer is higher. I have been tossing the ARP washers and using the OE ones to reduce this problem. So what happens is you torque them up near the point the head wants to yield and a few heat cycles the head yields a bit under the washers so stress and clamp force is reduced. This causes a reduction in clamp force, again this is bad.

Bob

Hmm. I have to double check the sheet mine came with and maybe that will jog my memory. I believe the first time I put the head on I torqued to 65-70 ftlbs ... but I had the head off at one point and probably followed the "using 30 wt " torque of 85 !!!!

I will do a lot less next time.
I haven't had any issues yet.

I think it was the 85 number that killed my head. one of the bosses cracked and the crack went into the water jacket.

Bob

I'll be torquing mine to 52 ft lbs.

I did mine to 70ft/lbs... :(

This should be in the useful threads sections

Oh shit, my M3 with its newfangled uber-torque ARP head studs just blew its gasket.
I hope the kilobuck ported head isn't trashed. :(

FYI, I ordered two sets of studs for a couple of cars at the shop this week. Just opened the first box to install them and the instructions say 80 ft.lbs with ARP Ultra-Torque fastener lube.

I will be torquing to 65ft.lbs.

Torquing the studs to 65 ft-lbs puts about 740lb of axial load in the bolts, or slightly less using the lube on the threads. (this assumes 0.15 friction factor, but with the lube it's in the range of 0.11-0.17 from what I can tell) I'm not sure what the stock bolts are shooting for or if they're torque to yield bolts, so it's hard to compare. The 48ft-lb torque produces about 550lb of load in the bolt using the same friction assumption as above.

80 ft-lbs just can't be right.

Stock torqe specs arent anywhere near yield in the stock bolts.

Need to calculate the area under the washer and see if it is enough pressure to yield the aluminum head Id guess the material would yield at about 41,000 psi cold for the cast aluminum head. As the head gets hot the clamp load increases and yeald occurs at a lower level. ARP studs also have smaller OD washers than stock which isnt helping things.

quick guesses I come up with .291 for area makes 2543 psi. shouldnt yield when tightened to 65 FT-lbs. bit more involved to look at effects of thermal expansion. The head will wan't to grow a lot more than the bolts when things get hot.

Bob

haha, I should just do a quick FEA of it next time I'm bored at work.

I'll be putting the head back on my car this weekend hopefully. I'm planning on torquing them to 65 ft lbs as well.

Found this today with some old papers in the garage. Installed mine before this thread started and probably followed the instructions. Guess I will just need to wait and see what happens.

Received an email from ARP after the floods destroyed all our build diarys,

Sorry to hear you lost some things in the flood! Here are the torque
numbers you need. They are the same for both the ARP Ultra Torque and
ARP Moly Lube.

Rod Bolts 118-6401 = 38 ft/lbs
Head Studs 218-4701 = 80 ft/lbs
Main Studs 218-5401 = 60 ft/lbs

Regards,

Alan Nichols
Sales & Technical

Automotive Racing Products
1863 Eastman Ave.
Ventura, CA 93003
Toll Free: 800-826-3045
Ph: 805-339-2200
Fax: 805-650-0742
Email: alann@arpfasteners.com
www.arp-bolts.com



So I think I follow Savs recommendations

Terry

I am pretty sure 80 is way too much for our aluminum heads. The original ARP engineer who set up the studs for the application said 48 I believe and the stock specs for the OE bolts which should provide a lot less clamp force per torque amount is 56-60.

Bob

So if the head bolt spec is off then what should the rod and main bolts be torque to? I am about to rebuild my engine.

Have a great day,
Jared

Would there be benefits to using oe sized washers with the head stud kit? Perhaps the higher torque numbers would not damage the head with more area under the washer for said tq to be exerted onto or would it be such a small increase in od that no difference would be realized?

I haven't seen the size difference but any time you can increase the area that will reduce the pressure/stress exerted on the face. Even small changes in area should produce a decently reduced stress. P=F/A

I can probably take some pictures tonight. I ditch the ARP washers and use OEM ones. They appear to be the same hardness but the OEM ones have a significantly bigger OD.

Bob

I torqued mine to 80ft/lbs a couple years ago, which seemed ridiculous when torquing them down at the time. I have, however, ran the engine without a belt on the water pump for 40 minutes in traffic (Had no water temperature gauge) before the upper radiator hose literally blew off the radiator. In normal cases with factory head studs, this would call for the head to be machined for sure. I just put the hose back on, threw a belt on, filled up, and I haven't lost coolant ever since.

Surprising that ARP would tell you this. The ARP2000 bolts that M-Tuned ships with their rods specify a stretch spec, not a torque spec. I've found that in order to get the ~.005-.006" stretch spec (IIRC), they wanted around 55-60ft.lbs of torque, not 38.

When I contacted m-tuned about torquing the rod bolts they specified 40-45ft lbs if not torquing to the stretch value.

Sorry to bring this back up. I just pulled the head, and plan on installing the new gasket this weekend. I originally torqued the nuts to 80 ft lbs per the instructions using the arp moly lube. After reading this thread it sounds like 65 lbs is a better option. Do I need to get more arp moly, is there a substitue, and do I need to measure the length of the threads for stretching with a micrometer? Keep in mind the threads had moly only when initially torqued, and now they will probably have a little oil on them. What is the recommendation for this scenario.

EDIT: It appears that ARP is now using the "ultratorque" lube which really minimizes the variance between torque stages. I think I screwed the pooch by tightening once, then immediately checking the torque again then buttoning everything up and never looking back. It appears that a person should probably use 8 separate torque cycles at the desired torque. How many cycles leading up to the desired torque before starting the 8 cycle retorque session? How long between cycles should a person wait before starting the next torque cycle???

Example: Pre torque 25%, 50%, 75%, 100% then 7 more cycles at 100% torque

+1

In for answer.

Just an FYI. This is why I said eight cycles to tighten. Then if you use assembly lube or motor oil you can be sure that you are getting the torque that you want. It also appears that a torque cycle is defined by tightening to spec, then loosening. I was unaware of this. I thought it meant tighten to spec, wait for any stretching then hit it with the torque wrench again to check. Using ARP assembly would clearly save a bit of time.

https://www.miataturbo.net/picture.p...pictureid=1840

That is very good info. Thanks for sharing.

I will say that the BP is not known for blowing head gaskets, and unless you are building a mega high horsepower motor, 8 torque cycles, tightening and loosening, and choice of lubircant is not overly important. Clamping a miata head to block is pretty forgiving of discrepencies in technique, with the exception of over torquing which has already been discussed.

There is no time component to fastener stretch. It stretches as soon as you preload it.

8 torque cycles is absolutely ridiculous. Use their recommended lubricant, torque it in 3 steps, and don't untorque it. All you are doing is uncompressing and recompressing the gasket, which is a bad idea.

Thanks Sav! :bigtu:

Back from the dead.

I just called FM and they say the 48lb ARP head stud number is not used by them anymore. They said 60-65lb for both the ARP head and main studs when using the ARP moly lube.

Why would we want to exceed the OE torque spec and thus clamping force if we know that the ARP studs are already stronger than OE bolts? Isn't the benefit in using the stronger studs? Or is there something to be gained by increasing the clamping force?

I'm reluctant to use ARP main studs at a higher torque if it forces a line bore since it adds $$$ to the build.

The increased yield of the material is of little use in stock preload applications. The modulus of elasticity which would determine the "clampyness factor" is pretty well absolutely constant for most steels. Unless you need a higher torque load on the bolt/stud the additional material strength isn't going to do you any good. In short... the studs should not apply any additional clamping force under stock pre-load. Higher then stock pre-load can cause problems as mentioned...

That being said, the tensioner bolt on my power steering pump broke today. I could just be bitter.