ARP Head stud torque

[Fixer]

When you buy ARP head stud kit the recommended torque value given is super high at 38 foot pounds.

I'd never do 38 (did 28) but I wanted a reason why they recommend so much higher than the factory 24.3 ft lbs.
I understand it's a different bolt but that's a big jump. At operating temperature our motors grow about 2.5mm btwn camshafts. That is like tightening the head stud nuts another 180 degrees.

Here are my emails to Jay at ARP who is in R&D. I would not do 38.

[wildcat077]

ARP has their own torque specs ... for instance on my 944 2.5 race engine they want 100ft/lbs of torque as where Porsche asks for 66 ft/lbs , while the later engines 87 and on use the degree torque method.I'm kind of skeptical as well as i can imagine pulling the threads out of the block with 100 ft/lbs , i go halfway at 85 ft/lbs , although my engine is a non turbo but it does have a lot of compression.

[Fixer]

ARP has realized their error and will now recommend 28 ft lbs NOT 38.

Matt

[Fixer]

Originally Posted by wildcat077

ARP has their own torque specs ... for instance on my 944 2.5 race engine they want 100ft/lbs of torque as where Porsche asks for 66 ft/lbs , while the later engines 87 and on use the degree torque method.I'm kind of skeptical as well as i can imagine pulling the threads out of the block with 100 ft/lbs , i go halfway at 85 ft/lbs , although my engine is a non turbo but it does have a lot of compression.

You were smart to question.

My guess is you're still higher than you should be though. If our 911 value is 28 or 4 pounds higher, yours is likely only about 10 ft lbs higher or 75 ft pounds. You should contact ARP.

Matt

[Jonny042]

Thanks for posting this, Matt.

When I last used ARP studs I used a lower torque value like you did - 32ft/lb I think.

[wildcat077]

Matt , i’m currently building another race engine and i will surely contact ARP regarding their torque values …
I honestly think 100ft/ lbs is overkill , if you do the math you are torquing almost 30% more than what Porsche recommends ?
This is not a Formula One engine, just a little old 2.5 !

[mikedsilva]

Very interesting... I wonder if anyone that has used these studs, with 38lbft, has had a problem yet?

[Fixer]

Originally Posted by Jonny042

Thanks for posting this, Matt.

When I last used ARP studs I used a lower torque value like you did - 32ft/lb I think.

Yeah no problem. You can always crack them and go with 30 next valve adjustment.

I'm going with 27 or 28.

I asked about their assembly lube and it's coefficient of friction which Jay says is about the same as 30 WT oil.

I let him know his tech support told me it was super slippery and much lower than oil.

32 is probably fine but over 35 would be bad.

Matt

[Fixer]

Originally Posted by mikedsilva

Very interesting... I wonder if anyone that has used these studs, with 38lbft, has had a problem yet?

These engines run so well even with pulled and broken studs I imagine there are issues but they don't know.

Torque is torque. 38 is too high.

I dont want to get on ARP's $%#@ list here. I really like their products.

Matt

[Fixer]

Originally Posted by wildcat077

Matt , i’m currently building another race engine and i will surely contact ARP regarding their torque values …
I honestly think 100ft/ lbs is overkill , if you do the math you are torquing almost 30% more than what Porsche recommends ?
This is not a Formula One engine, just a little old 2.5 !

Yeah and maybe crack your first engine and retorque to 75.

We don't want our engines too loose either but too tight will deform and stress.

I'm going with 27-28 but factory is 24.3 so now I'm relying on their equivalent testing.. but it know 30 is okay so 28 will probably remain my number.
Matt

[Fixer]

I'm repairing a 930 case now that has 10 pulled ARP head studs. 7 on the left bank and 3 on the right bank.

To test and find all that pulled I torqued all to 60 ft lbs. The ones that handled 60 no problem I will leave alone. Once the Snap On wrench clicked at 60 I immediately backed them off.

The 10 that are pulled I will Time Cert. The motor ran strong but I noticed that subtle loose exhaust sound.

When I checked the head studs initially I used 24 ft lbs and and several just wouldn't tighten. I looked with a mirror and could see the nut climbing up out of the head.

60 ft lbs found the rest. Some still sorta hold and pull slowly.

This is why I decided to contact ARP. This engine was just done using ARP I don't know for sure what torque was used but I suspect 38 bc the tight ones that did not fail were really tight.

Matt

[stownsen914]

10 pulled studs in an aluminum case is impressive

[Jonny042]

Originally Posted by Fixer

I'm repairing a 930 case now that has 10 pulled ARP head studs. 7 on the left bank and 3 on the right bank.

To test and find all that pulled I torqued all to 60 ft lbs. The ones that handled 60 no problem I will leave alone. Once the Snap On wrench clicked at 60 I immediately backed them off.

The 10 that are pulled I will Time Cert. The motor ran strong but I noticed that subtle loose exhaust sound.

When I checked the head studs initially I used 24 ft lbs and and several just wouldn't tighten. I looked with a mirror and could see the nut climbing up out of the head.

60 ft lbs found the rest. Some still sorta hold and pull slowly.

This is why I decided to contact ARP. This engine was just done using ARP I don't know for sure what torque was used but I suspect 38 bc the tight ones that did not fail were really tight.

Matt

OK, not trying to be difficult, here, but...

Not sure I follow the reasoning for this "test". IMO all this proved is you can pull studs from a case if you torque them hard enough, ruined a set of studs by stressing them past yield, and probably warped the heads and case?

I think this thread would get a lot more traction in the engine rebuilding forum. This has been beaten to death over there.

[Fixer]

Originally Posted by Jonny042

OK, not trying to be difficult, here, but...

Not sure I follow the reasoning for this "test". IMO all this proved is you can pull studs from a case if you torque them hard enough, ruined a set of studs by stressing them past yield, and probably warped the heads and case?

I think this thread would get a lot more traction in the engine rebuilding forum. This has been beaten to death over there.

Several would not click the torque wrench at 25 ft lbs bc they pulled while the car was at operating temperature.

But there are different degrees of pulled. 60 pounds for a few minutes cold would not hurt the stud but it will find the bad threaded case openings and did. My test given the situation was sound. "You had to be there"

This is a very important subject Jonny042 we need to protect our buddies so their hard work is ruined over an oversight by ARP. I'm not looking for any notoriety lol.

Matt

[Fixer]

Originally Posted by stownsen914

10 pulled studs in an aluminum case is impressive

Absolutely 10 are bad and kept pulling at about 30 ft lbs and never made it close to 60 which I image is on them at operating temperature with motor expansion.

When case threads were chased (do not recut) this can remove more thread material than we think. I'm finding out more..

A little wobble of the stud is fine when assembling but excessive wobble is not. If you use Loctite the cylinders heads and cam boxes must be torqued down quickly before it sets or it sets with Loctite on the leading edges of the case threads which will collapse under loads

We need to be very careful when cleaning out the threaded blind stud holes of our cases!! A little to aggressive and you'll be pulling your engine apart in 1000 miles.

Sorry to those this subject bores.

If you want this moved go for it.. I wanted to do my part and have.

ARP will likely revise their torque recommendation bc 38 is way wrong. Torque is torque.

I said all I need to say here. Have a great weekend it's driving season again!!
Matt

[Jonny042]

Originally Posted by Fixer

This is a very important subject Jonny042 we need to protect our buddies so their hard work is ruined over an oversight by ARP. I'm not looking for any notoriety lol.

Matt

Absolutely!!! Like I said, thanks for sharing the correspondence and for bringing this up.

I do share your concern about that 38 pounds!!!

One of the things I learned in my research on the topic which I found counterintuitive is that the same torque on a fine thread and coarse thread will result in a relatively similar clamp load on the fastener (in our case the head studs). Not the same, but somewhere in the range of 10-15% greater for the fine thread.

This is relevant because Henry Schmidt who's done a great job designing his Supertec head studs (with fine threads on the nut end) specifies varying torques for them depending on application:

Originally Posted by Henry Schmidt

SUPERTEC PERFORMANCE HEAD STUD KIT INSTALLATION INSTRUCTIONS
1) USE BLUE LOCTITE ON CASE END (10 x 1.50)

2) WE SUPPLY SUPERTEC THREAD LUBE WITH EACH KIT BUT YOU CAN USE LIGHT
WEIGHT MOTOR OIL OR ANTI SEIZE ON CYLINDER HEAD END

3) CLEAN CASE THREADS COMPLETELY
We recommend a thread forming tap (1.50x10 PD-6 6-N) for this application

4) TO INSTALL STUDS, DOUBLE NUT WITH THE GOLD NUTS PROVIDED

5) INSTALL STUD UNTIL IT BOTTOMS AND TURN OUT 1/4 TURN
******DO NOT FORCE THE STUDS INTO THE CASE*******

6) INSTALLATION LENGTH IS NO LONGER RELEVANT

TORQUE SPECIFICATION + or – 2lbs STANDARD TORQUE PATTERN IS MAINTAINED
a. 2.0 aluminum case 30 lb/ft
b. 2.0, 2.2, 2.4, 2.7 ( all magnesium cases ) 26 lb/ft
c. 3.0, 3.2, 3.6 aluminum case 30 lb/ft
d. 3.0, 3.3, 3.6 aluminum Turbo 32-36 lb/ft
THERE IS NO RETORQUING NECESSARY

So even though the ARP nuts are coarse threads and the Supertec are fine, the torque values would be somewhat comparable, keeping in mind the 10-15% difference.

In my application 30 ft/lbs would be recommended for the Supertec studs. To get a similar clamp load (of course that would depend on all things being equal which they rarely are, but given the lube provided with both studs they should be similar) you would need a bit more torque on a coarse nut.

So, I chose 32 ft/lbs. I wanted a slightly higher clamp than stock due to the plain sealing surface on the 3.2 Carrera cylinders in the motor I was building.

Given the new information from ARP I will use the same for the 3.4 I'm gathering parts for now. Already have the ARP studs I was really happy with them in the last build. Some things are subjective and intangible (like your testing!) but they just "felt" right going together.

[Fixer]

Originally Posted by Jonny042

Absolutely!!! Like I said, thanks for sharing the correspondence and for bringing this up.

I do share your concern about that 38 pounds!!!

One of the things I learned in my research on the topic which I found counterintuitive is that the same torque on a fine thread and coarse thread will result in a relatively similar clamp load on the fastener (in our case the head studs). Not the same, but somewhere in the range of 10-15% greater for the fine thread.

This is relevant because Henry Schmidt who's done a great job designing his Supertec head studs (with fine threads on the nut end) specifies varying torques for them depending on application:



So even though the ARP nuts are coarse threads and the Supertec are fine, the torque values would be somewhat comparable, keeping in mind the 10-15% difference.

In my application 30 ft/lbs would be recommended for the Supertec studs. To get a similar clamp load (of course that would depend on all things being equal which they rarely are, but given the lube provided with both studs they should be similar) you would need a bit more torque on a coarse nut.

So, I chose 32 ft/lbs. I wanted a slightly higher clamp than stock due to the plain sealing surface on the 3.2 Carrera cylinders in the motor I was building.

Given the new information from ARP I will use the same for the 3.4 I'm gathering parts for now. Already have the ARP studs I was really happy with them in the last build. Some things are subjective and intangible (like your testing!) but they just "felt" right going together.

Cool thanks.

I had my motor out for a few things and installed new base gaskets and went with a solid 26 ft lbs on my ARP head studs. Factory being 23-24 ft lbs. I thought a lot about it.

Also, if you look at other aluminum motors 21,22,23 ft pounds is the number a lot. 38 was insane.
Type 4 VW around 21, a new Min Cooper S (I have one) is 22-23 or 20 then 90 degrees, earlier 911s: 21 ft lbs and so on. We also have (4) studs per piston. If you look at other torque spec like the cam boxes that number is 18.3 ft lbs. I'm being cautious. I can always tighten them if they loosen but I don't think they will.

I compared factory hardware and finish to ARP's which is very smooth and slippery and made my decision to not do 28 ft lbs. I used assembly lube and 5W/30 synthetic on nuts and washers.

I want the value that is lowest but tight when cold.

I'll follow up with how it goes.

Matt