Cylinder head stud exposed length........
 

Use 'A' to measure the recommended 135 mm height.

Tony

Are you guys sure? Henry wrote to measure from top of machine surface at spigot, cylinder sealing surface.

Maybe your 'wobbling' issue has same root cause as mine....depth.

I don't think my wobble issue was a result of the depth. It was me using the wrong tool to clean the threads. The studs are loctited in now and they are not coming back out with out a torch. I test fit the #1 head to see if I could still get a tool into the end of the barrel nuts after they're torqued. I could. Torqued them down and removed them. But there isn't as much room as I'd really like. I think the answer for me might be to use a 12 point nut, like an ARP on the steel stud. I don't know. Pretty frustrated right now. Trying to decide if I really want to remove these studs over 2.5mm of threads. Basically 1.5 threads on the stud.
I'm just mad at myself. I should've just followed Wayne's book there instead of over thinking it.

Tool
 

If it makes you think any better I think I used the wrong tool too (Essentially a tap, not a thread cleaner... It also sounds like one or both of us got bad depth advice from someone who should have known better - mine was just easier to recover from..)

How much Loctite Red did you use. I am going to switch from blue to red but don't want to overdo it..

Thanks
Sam

It was not to lose before the locktite i could just feel a slight movement

I didn't get any bad advice really. I just did some searches on stud height. I was sure that every one was talking about the spigot sealing surface since it's a machined flat surface. The flanges at my head stud bosses are not that flat. I used an ARP clean-out tap, but it still must have undercut the threads.

As for the Loctite, I used a drop in the boss itself and a thin bead across the top of the stud threads. I don't know. Like everyone else I want the car to be as perfect as I can make it. But, sometimes I think perfection can be the enemy of good. Like I said, those studs are not coming out without moving heaven and earth. Is it worth it? In my case I'm not so sure. I think I could put a 12 point Raceware nut on the studs and that would probably work fine. Although the barrel nuts will work too. Just makes me mad that I made another stupid mistake.
Originally taking them out at tear down was easy by comparison to the 2 I did try. All of my original dilivar studs came out without any heat at all. That was another lesson I would definitely impart to someone else. If your steel studs look good, don't remove them. And don't use any form of tap on the head stud bosses. Thread chaser only. Test your rod and chain holders to make sure they are not too wide.

Did you get yourself a copy of Bruce Anderson's book? That and Wayne's book are godsends!!!

If the thread is engaged by more then 1.5 x diameter then 'wobble' won't change much and will really be due to the fit of the threads.

Once the stud is tightened there is a tensile force present and this will pull the stud into the correct alignment and this will be stable.

The Class of fit doesn't have much of an effect on the tensile strength of the stud within a class2/3 range although if it is very loose the thread in the case will be more likely to strip.

If the gaps are too big then there could also be an issue with the adhesive when the studs try to pull into line although the lower strength adhesives are more tolerant.

There are many different tolerances of taps. The Forming tap size that seems to work the best for us. 10 x 1.5 PD-66-N.

The stud install height for standard Porsche style hardware on a pre 964 engine is generally measured from the cylinder spigot (B in the illustration) where the cylinder meets the case. 132.5 to 134.0 mm. The other area (A) is quite often not (I hesitate to say never but I've never seen it) machined to any consistent specification.
Stud install height is a function for cylinder height (with gaskets) and head thickness (varies with machine work).
If the spigot is machined and the heads are machined the sud install height should be adjusted or at least considered.
When building a long rod engine with stock hardware this becomes a more critical measurement.

http://forums.pelicanparts.com/uploa...1392998208.jpg

Now I am confused - two different views resulting in around a 4mm ultimate height difference in stud position (Approx height of spigot above machined pad A).

Thanks Henry. I was sure I had read that before. My flanges are not machined flat, very well atleast. Even have what looks to be grinding marks. So my studs are now 1 mm too tall instead of 3. Which makes sense because I tested fitted #1 and with gaskets and washer installed there was 11.4 mm of stud threads to tip beyond the washer. If it were 3mm shorter than there would only be 8.4mm. I heard someone say you should have no less than 10 mm of thread.

I'm assuming the height is really only important due to the barrel nut. Which makes the Supertech stud kit even more appealing to me right now. On the next one I will definitely get those.

What was Porsche's seeming fascination with barrel nuts anyway? I can see them needed at cam towers. Just seems like a quality automotive flange nut would work just as good?

Henry beat me to it, but i'll share my thoughts as well since I typed it up already. Here's my take, for what its worth, as i'm no expert by any stretch of the imagination. Just someone who's spent WAY too much time on this forum over the last 14 yrs. 14yrs........ holy cow.

• I checked my tiny little SC and Carrera factory Porsche bible spec books and no mention in there about installed height of the studs.
• Checked Bruce Anderson's Peformance Handbook and no mention of installed stud height in there. Maybe I missed it because despite being a great resource of tech info, the technical information bounces around alot in that book
• I checked my old 1987-1989 Carrera microfiche (yes, I actually have microfiche and actually went down in the basement, literally dusted off the microfiche machine (which I "stole" from work when we replaced an old unit) to scroll through fiche images) and found nothing in engine fiche slides about stud height, despite reading clear information on removal of broken dilavars & installing new.
• I also checked the 964 & 993 documentation I have. Those are measured from the stud hole because there's no spigot step on the 3.6 cases.
• Wayne's book and the Bentley manual (mine is a 84-89 Carrera manual) clearly picture the measurement taken w/a ruler from the "machined" area around the stud hole. That doesn't make it gospel. Just pointing it out.

I use quotes around "machined" there because machined is a questionable word choice. Like Henry said, the spots on the case where the stud holes are drilled are not flat, so that doesn't make them a very good reference point. I looked at the only case I have available right now, which is my racecar's bare 3.0L SC case. It's been worked over in a lot of areas, so I don't know if my spigot surfaces are original/have not been decked. But I measured a variance of 0.12" to 0.14" between the spigot and the stud hole surface, checking numerous locations . That's a difference of 3 to 3.5mm.


So that ~3mm difference between the spigot deck and stud hole would effectively make a stud installation 3mm shorter than the 135mm target if you were using the stud hole surface as your reference. Shorter is not necessarily a bad thing when you consider the goal here is to make sure the stud is not excessively long, which would make the stud protrude further into the barrel nut and reduce the depth your hex bit has on the barrel nut tooling. With the stud deeper into the case, you also have to make sure the barrel nut is getting enough "grab" on the stud threads, especially considering the Porsche steel studs have a really short length of thread on the head side of the stud

Also, I looked at the difference of threading a stud into the case both ways. When you use the stud hole as a reference, the stud is reallllllly close to bottoming out. Bottoming is bad. Whereas using the spigot deck gives you more clearance from the bottom of the hole.. In either case, I don't think it's a big deal because both end up with plenty of thread engagement in the case.

If the barrel nuts are a concern, get rid of them and use a good hex flanged nut like the fancy factory Porsche 12 pt 3.6 flange nut. ARP also sells a 12 pt. M10 x 1.5 nut in blister packs.

http://www.summitracing.com/parts/arp-300-8365/overview/

Porsche has changed their threadlocker story over the years it seems. Red loctite 271 has been the norm for head stud installations over the years. But if you look at the info in the 993 manual as an example, they switched to 640 or 649 bearing retaining compound. For the rest of the studs the manual says "Note: Unless Indicated otherwise, apply Loctlte 270 to all stud threads when reassembling the engine!" 270 is medium strength green........ :rolleyes:

You can go nuts thinking about the "proper" threadlocker to use. Can't go wrong with red 271. Its high strength (requires heat to remove) for fasteners up to 1" dia. Is it overkill? I think so. Henry recommends & provides blue threadlocker with his studs, so that should tell you something right there.

Man, this thread has been very informative. Thanks everyone.

I must admit I am still not clear.
It seems everyone agrees that the measurement should be right around 134mm and Blue Loctite works, Red is belt and (hard to remove) braces.

I am using barrel nuts - there still does not to be agreement as to whether to measure this from the pad or spigot - which will result in a 3mm difference... there MUST be a single right answer....

Wish I had taken a reference measurement before removing the old ones...

Sam, I'll let one of the more experienced guys chime in, but next time I will measure from spigot sealing surface to end of stud for 133mm.

Slip a cylinder and head on and see where the barrel nut fits.

Will do - don't want to sound like I'm complaining.....threads like this have helped with every step of Jezebel's birth!

http://forums.pelicanparts.com/uploa...1393013274.jpg

Listen to Henry!