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

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.

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?

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.

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...... ;)

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?

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

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

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.

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

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

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 ?

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

KTL,

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

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

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 ?

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.

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.

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.

The topic of “head studs” is thwart with many opinions. Some valid and some steeped in historical “wife’s tales”.

Let me start with this. I believe many failures can be attributed to installation issues and the head stud takes the blame, always. In some cases, poorly written and vague installation instructions can be to blame. Understanding who you are selling to and their ability is important.

Many DIY engine assemblers assemble their engines in their home garage on the weekends, with a beer can and a book written on how to rebuild a Porsche engine, beside them. I know that better instructions and “why” certain installation procedures should be considered are important.

Years ago, we use to make our own studs and sell them. I think we had the only aftermarket studs sold by a engine company, other than fastener manufactures. I decided to stop selling studs to outside buyers because so often the issues were installation. We kept our studs inhouse for our own use. I also hated the vitriol spewed out by some suppliers about other competitor studs. One company that will remain nameless here, is particularly bad about this. Sell your studs because they of what they will provide not because you think others are junk!

Studs used in engines need to be used based upon the engines use, not because they are shiny and look nice. Are factory Porsche studs junk? No, but they did have issues with studs some years ago and since then the “all thread” types are very good. Are any of the other aftermarket studs sold today, no good. No would be my conclusion. I don’t think any are bad, some are better than others and some are over sold.

There was a lot of bad information put out there about ARP studs some time ago. We have used many sets of ARP studs over the years, in Porsche and in other engines. One engine we are involved in makes well over 3000 BHP and built with only ARP fasteners. In both the air cooled and water-cooled Porsche engines, selection of the right stud and proper installation is important. The ARP studs sold for Porsche engines have only been sold as stock replacement studs. I do not think anything sold by ARP to date has ever been built for high performance applications. However, they certainly have been used in high performance applications.

There are other very good studs sold. I have referenced the ARP stud as this stud got a bad wrap unfairly in my opinion.

Our use of any stud has shown up issues with installation. As an example, the water-cooled engines with single cylinder heads each side show up the installation needs required. You do an initial torque “seating” then go back in sequence and do an angle tightening. After the initial torque seating is complete, the nuts on the middle cylinders will be loose. Same can happen on air-cooled heads.

I have decided to write some assembly instructions that will go along with the new studs we are involved with. These studs are directed towards the high-performance world, not so much stock engine use. For stock use, the factory “all thread” stud is a proven stud. The cost is the issue now, so some of the good aftermarket studs can be a more cost-effective stud.

The topic of thread integrity has come up. Thread chasing taps verses thread cutting taps. A thread forming tap is supposed to straighten up the original thread back to its cut shape. Without removing material. Some care needs to be had here as some threads are so far out of shaped that these taps have been known to break. In the US, only “H or h” is used to classify threads, I think. Capital “H” is used to classify Internal threads and the numbers between 4 and 8 are used for internal threads. In most cases in the aerospace industry, 6 is a common value. So, any thread classification used in this level of engines, will be 6H.

When you stretch the head stud to apply clamping load to the cylinder head assy, the thread in the case gets pulled hard. The thread material is a lot weaker that the steel stud. Threads get deformed some. Therefore, it’s important not to bottom out the stud in the case thread. The stud needs to turn when the nut is tightened. Once the friction increases and overcomes the torque or angle pressure on the nut the stud will stop turning and the nut will tighten. If you bottom the stud and it cannot turn, all you will do is to pull the threads in the case out of shape.

The use of Loctite on the stud threads in the case is something that needs to be done with care. If you are going to be pulling the heads on and off in some quick succession, like Drag race engines, then go ahead and Loctite the studs in. Or if you will tighten the head nut before the Loctite cures, use it with care. But if the Loctite cures before you tighten the head nut, you are in the danger zone of having issues. Often the Loctite gives way and you feel and hear a snap as the Loctite gives way when you are tightening the head nut. The torque wrench clicks, or the angle gets all messed up and you have no idea where you are. My advice is, do not Loctite the studs. Use some grease and back the studs out at least ½ turn. EPG sold by McMaster-Carr is a good grease.

Before you send out the heads for rewire, check the washer platforms for deformation. This is common. The platforms are not flat and now the washer contacts the platform only on the outer edges. Under the tightening of the nut, the washer collapses and there goes the accuracy again. In recent testing we have found a huge issue with accuracy, just in how the head washer contacts the head even with flat platforms. The new kit includes are new washer that addresses this problem.

How accurate is your torque wrench? Has it been calibrated recently. Do you leave it wound up or do you unwind the setting each time? Is it a quality wrench or is it a cheap brand? We take this part of the assembly very serious. To give you an idea, our Torque wrenches are checked every year. They cost over $2500.00 each and the values can be downloaded to files that show each fastener, its angle, its torque value, sequence, and a measured percentage of friction verse time to reach the desired torque and angle.

So, before you trash the heads studs, check your assembly procedures and do not take the assembly for granted.

Thread Chaser
 

Good gouge here!!!

My brother (Pelican "Cabmando") decided to use a thread chaser and broke it off in the block. The chasers are made of hardened steel - which made removal very challenging (difficult to drill into it to try using a remover). In the end, we boogered up the threads trying to remove the broken chaser and had to fix the threaded hole with a time-sert.

Gordo

Amongst Neil's very good points, this one stood out to me most because I recently cleaned up some old head stud washers and they're not all that flat. So it's good idea to get your washers flat by truing them up on a flat plate with some wet sand paper. It's also good to make sure the washer and head surface "bite" to avoid loosening.

This link below is not to crap on the ARP studs, but to point out the benefit in having the thick washer provide some roughness/friction against the head

http://forums.pelicanparts.com/porsche-911-technical-forum/993295-pulling-head-studs-arp-finding.html

Great stuff, Neil Harvey. Thanks for sharing.

The notion of a tap breaking implies some force beyond hand turning is required. Is the thread forming aspect of stud replacement best left to experienced hands ? I would think thread chasing with a old stud is a minimal torque affair.

From this other head stud thread, sounds like the Supertec stud is thicker... http://forums.pelicanparts.com/911-engine-rebuilding-forum/930172-raceware-studs-911e-engine-2.html

Interesting, Some of the head stufs threads come with what looks like some sort of Loctite on the thread ends which go into the case, would you clean this off or leave it?