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-   -   Another head stud thread (http://forums.pelicanparts.com/911-engine-rebuilding-forum/994901-another-head-stud-thread.html)

jellonailer 04-27-2018 10:34 AM

Another head stud thread
 
A few of you have commented on my head 78 3.0 Euro build, thanks.

I'm at a point where I need to decide on my head studs. I've read a butt load of threads, search is my friend.

Short history - Supposedly about 20k on engine from last rebuild. Many things wring including 4 broken rings, zero broken head studs. ALL the studs are non-magnetic, Dilavar. I feel I should replace all of them to steel. Threads say use the Dilavar on top is ok, but its small money to change all of them to steel and then I know it's done right. I don't trust anything on this previous build.
Fire away.
Thanks

Ken911 04-27-2018 11:03 AM

If you get raceware or ARP or supertech head studs they will never break or need replaced again. Just get the best ones your budget will allow. there are tons of threads saying this or that new or later type of dilivar studs work etc. But thos three aftermarket studs all work well and cost much less in the long run that tearing an engine down.

pampadori 04-27-2018 12:09 PM

If anyone is still installing dilavar studs they are doing the next owner of that engine a huge disservice. Go steel or ARP or Supertech.

I too had ALL dilavar on my engine. I looked at the serial number and learned that I had a 930/52 case from a turbo underneath all of my '83 non-turbo CIS equipment. They had just reused the studs from the 930 donor engine during the last rebuild. have you checked for that by any chance?

jellonailer 04-27-2018 12:16 PM

Yes, mine was not a turbo case but it is a 930/xx, can't remember the 2 digits. I think so too but I would prefer to go with steel rather than the upgraded. I'd like to put that money into the 964 cam.

Speedy Squirrel 04-27-2018 03:44 PM

The need for a stud that does not over-clamp the very thin walls of 95mm and bigger bore cylinders is not a made up thing.

Tippy 04-27-2018 08:32 PM

Quote:

Originally Posted by Speedy Squirrel (Post 10017584)
The need for a stud that does not over-clamp the very thin walls of 95mm and bigger bore cylinders is not a made up thing.

Hence why 993TT Dilavar studs are superior.......I think what you were meaning to say...... ;)

Peter M 04-28-2018 01:17 AM

Has anyone come across any data relating the stud material type to the effect on bore roundness and therefore horsepower?

Ie I can imagine the steel studs deforming the cylinders at normal operating temperatures to a much greater extent than the Dilavars.

Wonder if this is the reason Porsche persisted with the Dilavars for so long and why the 993TT's had them top and bottom?

Peter M 04-28-2018 02:10 AM

Great thread on Dilavars vs steel. The effect on cylinder roundness is touched on but no answer arrived at. Most of the discussion centres on the head sealing and maintaining head stud tension over all temperatures but well worth a read:

http://forums.pelicanparts.com/911-engine-rebuilding-forum/644752-993-head-studs-two-types-3.html

jellonailer 04-28-2018 03:23 PM

ok, thanks for the great comments. Though no one said it, bottom line is to quit being a penny pincher and just pay an extra $300 and get the ARP or Supertech. Don't have an issue doing the right thing, I just don't believe in bling for the hell of it.
Thanks

KTL 04-30-2018 02:04 PM

Note that the ARPs have been known to show loosening after installation. Some have found the use of their moly lube under the head of the nut contributes to this. The Supertecs stick good right from installation (no re-torquing required) and maybe it's on account of the serrated flange nut (actually a 928 rod bolt nut) biting into the precision ground thick washer?

Also note that the last of the naturally aspirated air cooled engines use all steel studs. The 964 engine is originally equipped with all dilivar (not the 993TT all-thread) and then the 993 came along with steel and then the 993TT uses the all thread. Basically Porsche was all over the place with their usage of head stud types.

A large number of people have used all plain steel on the naturally aspirated engines for a lot of years and no bad results. Lastly, if you plan on getting all new hardware as well? The Supertec studs are a great value. If you check Pelican's pricing on a set of steel studs, new washers and new barrel nuts? You're very close to the price of the Supertec stud kit. Just make sure the Supertec kit includes a thread forming tap for the case, which shapes the case threads to the same thread fit (same pitch as original- M10x1.5) as the precision studs.

pmax 05-01-2018 10:10 AM

That thread forming tap isn't a custom tool, is it ?

KTL 05-01-2018 02:07 PM

Well I haven't been able to find the same tap that Henry cites- M10x1.5 PD-6 6N

I'm not saying I can't independently find an M10x1.5 forming tap. I just can't find one with a 6N thread fit

pmax 05-02-2018 12:41 PM

What does the PD-6 or 6N for that matter mean technically ?

Cleaning and forming the threads properly appear to be critical. Is the 30 ft lb a conservative torque spec ?

KTL 05-02-2018 03:34 PM

PD typically refers to Pitch Diameter in tap terminology. I'm going to guess the other 6 is the number of chamfered or partial-height forming flutes down at the end of the tap which means the tap is a tapered tap. N is probably the type of coating the tap has on it.

Hard to find information on forming tap terminology because every manufacturer seems to use a different labeling system for their taps. Yamawa has some good information

https://www.yamawa.com/en/support/technical/index.html


The 30 lb-ft is the spec that Supertec recommends for the aluminum cases, non-turbo engines

http://forums.pelicanparts.com/uploa...1525297101.jpg

pmax 05-10-2018 08:49 PM

KTL,

Does thread forming mean the tap is designed to remove case material ?

LMFTFY
http://forums.pelicanparts.com/uploa...1526010461.jpg

KTL 05-11-2018 02:51 AM

Thread forming means the tap shapes the metal with pressure. It doesn’t cut/remove metal to make the threads

pmax 05-11-2018 01:19 PM

Quote:

Originally Posted by KTL (Post 10032950)
Thread forming means the tap shapes the metal with pressure. It doesn’t cut/remove metal to make the threads

Thanks for the correction.

Given that, it implies to me that the thread being formed for the Supertec stud is necessarily larger, in some dimension, than what's already in the case or is its only purpose just to clean out any Locktite or equivalent stuck in the case ? Posing this question differently, is the thread formed for the Supertec stud using this tool usable by standard studs for example ?

boosted79 05-17-2018 05:33 AM

Most just take an old stud and cut a couple thin grooves across the thread with a cut off wheel and that is used to clean the threads.

safe 05-17-2018 07:13 AM

Quote:

Originally Posted by pmax (Post 10033556)
Thanks for the correction.

Given that, it implies to me that the thread being formed for the Supertec stud is necessarily larger, in some dimension, than what's already in the case or is its only purpose just to clean out any Locktite or equivalent stuck in the case ? Posing this question differently, is the thread formed for the Supertec stud using this tool usable by standard studs for example ?

I think its the other way around. The threads in the case is on the tight side for an M10 and if you use a normal tap you will remove material and make the threads loose, therefore he specifies the exact tap to use without enlarging the threads.

I did like Boosted79 sugested and used an old stud.

pmax 05-18-2018 09:56 AM

Interesting.

Found this thread from the past where Chris_seven (it seems he also makes head studs for the 911 and whose posts appear highly technical) says

"ARP, Supertec, Casper Labs and any other stud with an increased shank diameter will increase the force on the thread produced by the thermal expansion of the cylinder."

http://forums.pelicanparts.com/911-engine-rebuilding-forum/790482-arp-head-stud-installation-instructions-vs-reality.html#post8453631

and has the same question as I did above about the need for the forming tap.

"The forming tap is an interesting idea do you know the class of fit after using a forming tap? I would guess that this will open the thread slightly and increase clearance which may make it easier to install the stud."

http://forums.pelicanparts.com/911-engine-rebuilding-forum/790482-arp-head-stud-installation-instructions-vs-reality.html#post7842555

I suspect this is water under the bridge stuff in 2018 but I will keep looking for that side by side physical comparison of the Supertec vs OEM thread.


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