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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.
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Old 04-27-2018, 09:34 AM
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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.
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Old 04-27-2018, 10:03 AM
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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?
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Old 04-27-2018, 11:09 AM
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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.
Old 04-27-2018, 11:16 AM
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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.
Old 04-27-2018, 02:44 PM
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Quote:
Originally Posted by Speedy Squirrel View Post
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......
Old 04-27-2018, 07:32 PM
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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?
Old 04-28-2018, 12:17 AM
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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:

993 Head studs, two types?
Old 04-28-2018, 01:10 AM
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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
Old 04-28-2018, 02:23 PM
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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.
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Old 04-30-2018, 01:04 PM
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That thread forming tap isn't a custom tool, is it ?
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Old 05-01-2018, 09:10 AM
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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
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Last edited by KTL; 05-02-2018 at 01:08 PM.. Reason: edited the thread size- mistakenly showed M10x10.5
Old 05-01-2018, 01:07 PM
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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 ?
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Old 05-02-2018, 11:41 AM
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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

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Old 05-02-2018, 02:34 PM
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KTL,

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

LMFTFY
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Old 05-10-2018, 07:49 PM
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Thread forming means the tap shapes the metal with pressure. It doesn’t cut/remove metal to make the threads
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Old 05-11-2018, 01:51 AM
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Quote:
Originally Posted by KTL View Post
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 ?
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Last edited by pmax; 05-14-2018 at 10:58 AM..
Old 05-11-2018, 12:19 PM
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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.
Old 05-17-2018, 04:33 AM
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Quote:
Originally Posted by pmax View Post
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.
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Old 05-17-2018, 06:13 AM
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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."

ARP Head Stud Installation - Instructions vs. Reality

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."

ARP Head Stud Installation - Instructions vs. Reality

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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Old 05-18-2018, 08:56 AM
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