Head Stud height question

[Green993]

The manual for the 993 says the head stud height is:

130.2mm -.5mm

Does this mean 130.2mm TO 130.5mm

or

Does this mean 130.2 minus .5mm (effectively 129.7mm to 130.2mm)

[redjb944]

I posted the thread on 964 head stud projection and rec'd the response 130.2-0.5. I interpreted this the same as you....130.2 - 130.5, with the mean @ 130.35 as you stated. I THINK this is correct; however, will be looking for other interpretations

[suprxman]

Your last sentence is correct for a tolerance range. 130.2 -.5 = 129.7.
Unless the Germans do it differently. I worked at DaimlerChrysler and we did it your way.

[Green993]

crap. That means I'm .15mm too tall. So the next question is: Should I go back and redo? I am at the point of just having finished tightening down the heads and can take the cam carrier/heads off as a unit. I'm leaning towards fixing it as this dimension is fairly critical IIRC. I'd be curious what effect this would have if left alone?

[Green993]

Originally Posted by redjb944

I posted the thread on 964 head stud projection and rec'd the response 130.2-0.5. I interpreted this the same as you....130.2 - 130.5, with the mean @ 130.35 as you stated. I THINK this is correct; however, will be looking for other interpretations

Did you do it yet? If not, at least you can benefit from my mistake!

[suprxman]

I'm no Porsche engine expert but .15mm is only .006 inches.Thats about 2 human hairs. Could that really make a difference?????
Come on Henry or other experts.

[redjb944]

No, have not installed the studs yet...still waiting on a (new) distributor drive gear to put crank in and seal the cases. sounds as if the correct answer is 103.2 (max) minus 0.5 = 129.7 (minimum)
However, I do agree with the poster that 0.15mm (.006") over the max length (assuming you hit 130.35 when installing) should not warrant pulling back apart. this last statement is an OPINION, not based on fact....good luck!!

[Henry Schmidt]

Originally Posted by suprxman

I'm no Porsche engine expert but .15mm is only .006 inches.Thats about 2 human hairs. Could that really make a difference?????
Come on Henry or other experts.

The design flaw in the Porsche head nut is that if the stud height is too tall the stud will fill the Allen slot in the nut pushing the wrench out.
This quite often goes unnoticed if proper torque is achieved. The problem comes when you try to remove the nut many years down the road. With reduced wrench engagement, corrosion and the electrolysis caused by dissimilar metals removing the nut becomes near impossible.
That said, shorter (within reason) is better than longer.

[Green993]

Originally Posted by Henry Schmidt

The design flaw in the Porsche head nut is that if the stud height is too tall the stud will fill the Allen slot in the nut pushing the wrench out.
This quite often goes unnoticed if proper torque is achieved. The problem comes when you try to remove the nut many years down the road. With reduced wrench engagement, corrosion and the electrolysis caused by dissimilar metals removing the nut becomes near impossible.
That said, shorter (within reason) is better than longer.

Hmm, this is a conundrum, what to do? I'm guessing it's gonna be 4 to 6 hours at least because of the heating required. That's if I don't remove the p/c's - just gently lift them away from the case and get the torch in there. Then I have to clean out the old loctite, etc..

Henry, would you say the .15mm is enough to cause the issue you address above. If so, I really need to fix this.

[Henry Schmidt]

Originally Posted by Green993

Hmm, this is a conundrum, what to do? I'm guessing it's gonna be 4 to 6 hours at least because of the heating required. That's if I don't remove the p/c's - just gently lift them away from the case and get the torch in there. Then I have to clean out the old loctite, etc..

Henry, would you say the .15mm is enough to cause the issue you address above. If so, I really need to fix this.

If your head stud install hieght is greater than the desired amount based on your head and cylinder dimensions you can adjust the measurement with a thicker head washer.

[Green993]

Henry, In my case I am using the 12 point barrel nuts with integrated flange. Is it okay to use washers with these? Also, what material should I use for the washers? Aluminum?

[suprxman]

How long would it take for me to get as smart as Henry?
Infinity times infinity.

[AlfonsoR]

Instead of a custom Aluminum washer, you could probably use the standard 911 head stud washer like this ... Pelican Parts - Product Information: 999-031-091-01-M260

Did you use red loctite for the head studs?

edit: oops, you are only .006" too tall? I don't think it would be worth going after.

[Walt Fricke]

I agree. 0.006" is simply not worth worrying about. We aren't talking piston to cylinder clearance, or some gear lash, or whatnot.

Absolutely do not use an aluminum washer. The factory (and all of the aftermarkets which come with replacement stud sets) washer is a hardened steel.

If you are really freaked, use a good quality thin steel washer and be done with it.

Even better, purchase a flange nut. You can get these with a 15mm wrench size, so you can get a socket over it down in that hole. Usual M10x1.5 thread size. The beauty of going this route is that you will never have a problem if the stud is a bit tall. The socket won't push out like Henry describes an Allen in the stock barrel nut can do.

I think that everyone doing a rebuild should toss the barrel nuts and use flange nuts. Unless they buy the Supertec kit, of course, which comes with all the needed hardware - including very nice 12 point flange nuts.

But in this case I'd just keep on assembling the motor and not worry at all.

[Green993]

Just to close the loop here. I took the heads/cam carrier off and redid all studs to proper height. Used red loctite. All is well.

[AlfonsoR]

I know Wayne recommends red loctite, but when i do my build I will use blue. I don't see the need to use the red, wrong application in my opinion.

[Henry Schmidt]

Originally Posted by AlfonsoR

I know Wayne recommends red loctite, but when i do my build I will use blue. I don't see the need to use the red, wrong application in my opinion.

+1
We ship our head studs with blue LocTite because we feel red is excessive.