Tom M'Guinn

Just in case my post was confusing, the torque angle procedure is for the nuts, not the studs. I do no think you want to torque the studs into the block like that.

Danno

Couple of background tidbits to clear things up. First, all steel studs will stretch with tension. Chromoly steels typically have a Young's modulus around 210Gpa. This stretch, and the materials' attempt to shrink back to its original shape is what gives the clamping pressure to hold parts together.

Second, steel underdoes a plastic transformation when their elastic-limit (yield-strength limit) is surpassed. That is, the material stops being "springy" like a rubber-band as it tries to contract back to its original length. It becomes a non-elastic paste, like clay or plastic with no clamping pressure. Additional stress just beyond the yield-limit hits the ultimate (tensile) strength limit where the material just separates into two. This limit is typically just 2-5% beyond the yield point.

How this relates to the stock studs, is that they are not torqued to their yield-point, in fact well below it. The yield-limit on the stock studs is at least 90,000psi with a ultimate tensile limit of 100,000psi. You're not going to reaching anywhere near that with 65-70lb-ft of torque. Just the fact the people have re-used their stock headstuds successfully means that the studs were stressed below their yield points. If not, the very next time you go to torque them down, they would just snap in two at slightest amount of tension.

"I'm gonna use the 30Nm + 60° angle method + Loctite. "

I've found the pages in the manual that relate to this. The old manual is on the left and it does specify a torque-number for the cylinder head. The 1991 updated torque specs are on the right:



Seb, I think you got the procedure mixed up. The 30Nm+60° angle is for attaching the block to the girdle down below. The procedure for the head is further down the page near the bottom.

Asarus

Thanks Danno

So how can i be sure my studs are correctly installed if i don't use a torque value ? I didn't mesure the height over the block before removing the old ones...

Danno

"So how can i be sure my studs are correctly installed if i don't use a torque value ?"

That's because torque values torque values can be misleading at the higher-torque numbers due to friction on the threads. That's why they say to use oil on the threads and it's a good idea to put it on the bottom of the nut as well so it slides on the washer easily. Even then each nut will have different wear patterns on its threads and will resist the wrench differently.

I recommend using new nuts and breaking them in on the actual studs they're on before final tightening. This is to smooth out the surface roughness and will give you more accurate torque-readings. So do the 1st two steps, 2Nm, then 90-degrees in the proper-sequence. Note the torque-value on your wrench at this 1st 90-degree. Then loosen them all up and start over. You will find that the torque the 2nd time around is less at the 1st 90-degree turn. That's because the surfaces of the new nut will have worn-in on the 1st tightening and will be smoother sliding the 2nd time. In both cases, however, the studs will be stretched to the exact same tension, even though the torque is different. Finish up with the 3rd 90-degree pass and you'll be all done!

BTW - if you really want to be technical, you can calculate the actual tension on the stud. Calculate the leverage of the angle of the threads multiplied by the rotation turned, etc.

Russ Murphy

"So how can i be sure my studs are correctly installed if i don't use a torque value ?"

The not-so-enlightening answer is set the stud height at 75mm as Jeremy suggests.
Use loctite, but the key is to install the head with the old head gasket and torque the nuts per the manual (use ARP's lube for consistent torque) and let it sit overnight.
Then remove the head stick your new un-crushed gasket in and torque to factory specs.
If you go through this little dance, the loctite will be liquid when you pull the stud threads up against the lower surfaces of the block threads displaciing the loctite which now will cure on the underside of the stud threads. If you put the loctite on and install the studs and wait for it to cure, when you torque the nuts you'll fracture the loctite that's between the two sets of threads. At least that's what Garrity told me to do.

alengyel

Can I make this a little muddier? Race Ware recommends using Teflon pipe sealant (I assume paste not tape), when they came out of my block the had been installed in this manner. But, they also recommend checking the torque after the first heat cycle. How does this factor in to the debate? Also, If I use Loctite, would green be sufficient in order to make removal easier? Thanks All.

Danno

I think you want to follow the manufacturer's recommended procedure when installing the studs. If you have the Raceware studs, follow their procedure and recommended torque sequence. Remember that due to the finer threads on the Raceware studs, the same torque reading of around 65-lb•ft will actually generate more tension and clamping force from the studs.

If you have the Porsche studs, follow their procedure. Can someone point me to the part in the manual on the studs installation? I can't seem to find it anywhere.

alengyel

Danno, thanks and if I run across the stud install in the manual I'll shoot you a PM.

AlexE

Danno.....

Following this logic why would anyone replace the stock studs if we dont ever torque them no where near their yield point?

I am trying to determine when is it necessary to replace stock studs.... without waiting for the obvious sign and having a studs stretch or back out?

Is there a hard and fast rule on determining how many times these studs can be stretched/torqued .....

Thanks!



Alengyel....

Would you mind letting me know where the factory install instructions are in the manual ? I cant find them either ?

superjet.1

This is a mecanics point of view not based on any book or theory. Ive replaced hundreds of head gaskets i can tell you the studs do stretch but not from over torque simply from age and heat. I replace head studs by milage every 100k regardless. Its a safe bet and follow the exact recomendations of the stud provider no fudging.

Danno

"Following this logic why would anyone replace the stock studs if we dont ever torque them no where near their yield point?"

In addition to what Travis said, the threads do wear out. Each and every single time you torque down the nuts, the threads on the studs build up some wear.

"I am trying to determine when is it necessary to replace stock studs.... without waiting for the obvious sign and having a studs stretch or back out?"

The technical procedure would be to measure the stretch of the stud before and after torquing to correct spec. A stud that's gonna fail will have a little more stretch. Kinda hard to do that on our cars.

"Is there a hard and fast rule on determining how many times these studs can be stretched/torqued ....."

Personally, I wouldn't do more than 3-5 headgaskets on a car before replacing the studs as well. You'd be amazed at how much of the threads get eatened up each time you torque them down. At some point, you end up with nuts that loosen on their own, or strip off the stud as you do the final tightening. You can feel the difference when you break in the threads on new studs & nuts (don't install them straight up the 1st time).

AlexE

Great info.

Thanks Travis and Danno!

I guess I will be replacing these studs.....

m42racer

It is also a good idea to have the Cylinder Head checked for the correct Hardness. With many of these overheated heads going back on, if the head has gone "soft" as it said, all the torquing in the world will never put the tensile in the stud, but crush the head. These Heads are heat treated and this hardness should be checked, along with all the other fundermental checks when rebuilding your engine. I wonder if this could be the reason why some have continuing bad luck with H/Gaskets. It could tell why some have better luck with the Std type over the MLS type. If the MLS is used, where there is little crush in comparision, the Head may deform and the torque be lost. Just a thought.

Laust Pedersen

The 20Nm/90º/90º procedure recommended by Porsche obviously assumes Porsche parts, which unfortunately also includes the head gasket. I assume the first 20Nm is to flatten the fire rings and compensate for other surface variations. With a known compressibility of the aluminum block, the head gasket and the cylinder head, the 2 x 90º angle provides a well defined clamping force between the head and the block. Changing (and in our case stiffening) any of the three components with WFG, MLSG or steel cylinder liners will change this relationship and in our case the clamping force will be higher.
Unfortunately I don’t know by how much and maybe not enough to be concerned about, since nobody have reported snapped studs or stripped threads using MLSG with steel liners.

Stretching (plastically) over time under stress is in material science called creep and to the best of my knowledge steel and aluminum do not creep even at the elevated engine temperatures. If steel was creeping (under ambient conditions) we would have a lot of sagging bridges and tall buildings fat at the bottom (it would appear that humans show creep ). Another material that does show creep is glass. The glass windows of old European buildings are thinner on top than at the bottom.

Hope this enlightens more than confuses.

Laust

superjet.1

Laust i do believe you are some what incorrect. Steel does creep as you put it thats why steel bridges are built with and arch in them and not flat. The arch inhibits sagging. Imagine this a 6 foot rod held only by its end laying horizontal of course after some time the oposite end not being held would sag to the earth due to gravity and the stress of the weight along its axis. This could be said for almost all metals. Aluminum would sag very little then simply snap off due to its brittleness.