Asarus

I'm going to put the new head studs (stock from Porsche) in a few hours and can't figure out what is the tightening torque for these studs ? (Porsche 951 1991)

I have the torque for the cylinder head but not for the studs..

Can you help me ?

Thanks

Asarus

I found 2 differents things about the torque...

Porsche manual says :
step1 : 20 Nm
step2 : 45 Nm
step3 : 70 Nm

Porsche technical datas (small booklet) says :
step1 : 30 Nm
step2 : 60°

I feel like the second method is the correct one (maybe both are equivalent), because it sets the head studs at a correct position to put back the cylinder head and nuts then...

Do you confirm ?

Jeremy Himsel

I've never seen a torque requirement for the studs.

Install them with threadlock and make sure the depth is accurate. I believe 75mm from the deck to the top of the stud is what i used but be sure to measure your specific application and give the threadlock some time to cure before installing the head.

The stud nut tightening is 20 nm then 90 degrees and another 90 degrees.

Asarus

Thanks Jeremy,

I use green Loctite to secure the studs and i tested the depth by mesuring the headgasket and cylinder head. It looks correct with the 30 Nm + 60° method.

The manuals says "crankcase upper and lower section (studs)" for the M12x1.5 thread, 3 steps :
20 Nm
40 Nm (sorry i said 45 Nm before)
75 Nm (sorry i said 70 Nm before)

That is for the head studs isn't it ?

Jeremy Himsel

The crankcase upper and lower specs is for the main bearing studs I believe.

Sam Lin

Hey Jeremy, if you see this, I sent you an e-mail at the work address and got the autoreply - send me an e-mail from your home address please.

Sam

Jeremy Himsel

Hey Sam,

Try Fomocoman@aol.com

I'm not at work this week....

Danno

"Porsche manual says :
step1 : 20 Nm
step2 : 45 Nm
step3 : 70 Nm


That might be for the NA cars, I've never seen torque-specs on the Turbo.

At the back of a lot of manuals, they'll be a section called "Updated torque specs" or some such thing. The current procedure is what Jeremy said:

step1 : 20 Nm
step2 : 90 degrees
step3 : 90 degrees

m42racer

The Head Studs should be installed hand tight only. Do not use any Threadlock. Torquing the Nuts will tighten slightly but allow the stud to "turn" until the nut clamps down on the stud. If the stud is tight in the block, the stud will try to turn and stretch the threads in the Block. Normal simple stuff here. Nothing new.

Tom M'Guinn

Just clean (and dry) the thread holes, and bottom the studs out, then back up as little as possible to get the height right. I assume the head nut torque specs listed above (correct for the 86-89) work for the '91 turbo.

(The 20/40/75 spec is for the crank girdle I believe, not the head studs.)

Jeremy Himsel

I'm interested in hearing why you should "not" use any type of threadlock on the studs other then for ease of removal.

Porsche used threadlock in this particular application. If the studs turns during the tightening sequence is will have a direct effect on the clamping force and actual torque value at nut/washer (more of an issue then threads stretching). The length of the studs on these motors are very long and have some lateral play at the tip as it is. On a freshly tapped block without thread sealant, this is compounded and can (however unlikely and extremely remote) lead to head walk.

While I don't see any real issues not using threadlock, I don't see any issues using it either (other then ease of removal). I've done it both ways with complete success.

Tom M'Guinn

Everything I've read says to use red loctite on the block end of the studs.

Jeremy Himsel

Same here, so I'm not sure why it is being recommended to install them just clean and dry without any threadlock?

Tom M'Guinn

Raceware actually uses teflon tape and no loctite, but they are not stretch bolts and are torqued with a foot-pound spec. On factory stretch studs, you are supposed to use the torque-angle procedure. If the studs turn while you are doing the torque-angle procedure, you will end up looser (less stretched) than needed. Red loctite will keep them from turning. It was used at the factory on new motors I believe.

Asarus

I'm gonna use the 30Nm + 60° angle method + Loctite. It seems to install the studs at a really good height. And by this method, all the studs will be installed in the same way