My Take on Cylinder Head Studs for Aircooled Engines

[Neil Harvey]

To answer the question by Henry, why did we decide to make our own Head stud? The proper answer should be, why did we decide to start making these again. We used to make and sell these over 25 years ago, before many others were making these. This was before the 993 studs came into existence, when all the Divalar issues were happening. Back then, the reasoning was easy to explain. Today, not so much.

I have gotten involved on this forum and Rennlist to help and give back to the community. I have my opinions on products and ways of building engines. I never assume I am right or it’s the only way, rather base it on what I see, what the engine application is telling me, all based on my knowledge and experience. This has been accumulated over many years and experiences, many of which I am truly humbled by.

My fondest memories are those that include my mentors, sharing their knowledge and experiences with me as I grew up in this business learning my “trade”. Showing me how to, why to, and when to. Then, as it is today, there were and are no books or papers to resort to when building brand new designs. However, there are the theories that are dated in time that give us benchmarks, baselines, foundations, known proven parameters that are used to guide design and development. But, in the real world you must know when to apply these theories appropriately, to match the results you are looking for. This means you cannot overlook or discard what you see. This is where the two worlds collide.

Applying this when rebuilding these Porsche air cooled engines, there are many critical issues that need to be considered. The material the engine case is made from, how old, how brittle, or soft it may have become with age and use. Does it have steel inserts fitted. Remember, just because it has steel inserts fitted, if the studs had pulled, the material holding the inserts is probably in the same condition as were the threaded bores. Are the decks level and straight where the Cylinders mate? Are copper or steel base Gaskets used. What is the class of the stud thread? Maybe a repair threading tap was used in the case? Was it a cutting tap or a proper roll type tap? Are the cylinders the same height? How soft/hard is the Cylinder head material. You can stretch the stud to its proper designed length but if the head collapse inwards around the stud, what have you achieved? This is where looking and understanding what you have in front of you is as important as any theory.

So, what does this whole rant mean. It means, without addressing these critical issues, it really doesn’t matter what stud you use. Certainly, the newer head studs are superior to the older ones. Also, I don’t hear about other brands of studs failing much either. Whenever this does happen, the background use and faults are never disclosed to fully understand the failure point. The fastener seems to get the blame always.

Why did we get back into the game? Simply, we are a company with a DNA that designs and makes our own versions of parts for these engines. Fasteners are one of many parts we have for these engines. Whenever we design something, it is always driven by a solid reason. Are we trying to solve a problem, create our own part under our brand, and can we improve on what is already out there? Whether its Head Studs, Camshafts, Connecting Rods, Crankshafts etc, we like to offer our own versions. But they are not for all builds. They must fit the build budget, the build end performance and fall under our ethos of a designed and engineered build. I started air cooled developments thread some months ago showcasing some of the new parts we have developed.

Our studs have several different features that others do not. I do not know what other stud makers make their studs from, but I would expect many use the same material as we do. Ours are made from 17-4 H-900 SS. This is one of the better materials to use in this application. We made our early studs from the same material. This new version of Head stud uses a 3/8” x 24 thread at the Cylinder head end. This is contrary to what others use. It is not a better thread than 10.00mm x 1.25, its purely so we can use a nut and washer that we use in other applications. Making 12point nuts is very expensive and requires large numbers to be made. These are made from Titanium. Titanium has been proven to withstand the heat cycles better than steel nuts do. It helps clamp the nut to the stud under heat loading better. The washer is also made from Titanium and acts as a heat barrier between the head and the nut. All to maintain the clamping loading we require. The only downside to this is, we supply those assembly hold down nuts for the Cylinders with the 3/8 thread. 12 come with each set of studs. We have added a hex’ed end making installation easier. You can install using a socket and not having to double nut them. Head stud installation, using Loctite or not, bottoming out or not is a totally different issue. I have made my reasoning on this known before. Its all about good building practices.

I’m turned off by all this back and forth over who’s studs are better. I at least have some knowledge of fasteners and their proper use. I cannot imagine how this comes across to those that just want good reliable information.

I have been drawn into discussions over the type of Ignition used. It got to the point where I just got turned off completely. Its not about which is better, it is always which is the better type in a particular application. I based my opinion on what I know and have proven on the dyno and in actual used in these large combustion chambered engines. If others have done the same research and testing and found other results, then that’s great. Then there are two types to chose from. I hope that customers come to me and require advice based on my proven results, not just what I think. I do my best to do this each time. When I do not know something, I tell them.

Are our studs better than 993 studs? Are our studs better than Henry’s. No is the correct answer as we have never tested any others back-to-back. We sell our studs based on our testing and the features we add and why. I never denigrate another stud sold by another company. However, I have been on the end of some who do. Don’t buy from them, period.

[reclino]

I think the standard thread is a great feature for cost savings and availability in the US. Metric 12 point nuts are tough to source. Titanium is probably a better choice of material vs making the nuts from stainless or even steel to prevent galling of the threads. 17-4 H900 is horrible for galling, against even carbon steel.
(Not trying to say this will be an issue with these studs we just have problems with it at work, one of our prime contractors made some jacking screws from 17-4 H900 and even with moly lube they don't hold up well.)

When you claim the titanium clamps tighter to the stud during heat cycling I am not sure what you mean? The heads do get hot, but not like exhaust studs. Is there a prevailing torque feature to these nuts? At the temps that the nut will see the aluminum head is going to go soft way way before even a simple steel nut and stud begins to lose clamping force. Maybe I am just not understanding your description of this. I know Chris Flavell had been talking about a full titanium head stud design, he thought it would be a good match for these engines. He would have jumped in on this discussion metallurgy. Too bad he is no longer with us.
Looks like a good stud.
David

[gsxrken]

Head studs are always going to strike a balance between durability (lasting the service life of an engine build), expand apace of the cylinder and head so as not to leak or have the head move around under boost, not pull threads in the case, deform the head, or distort the cylinders, and not loosen and need retorquing. We’re lucky to have a few good choices now that are functionally-equivalent in practice, if not theory. Thanks, Neil. Choice is good.

[Classic11]

I think i have read ALL, really ALL head stud discussions on this forum over the last couple of years for two reasons. I am trying to decide what do use for engines of course, what is the budget and what is the purpose of the engine. Second because I have studies fasteners and their application for many engineering trouble shooting in automatic transmission over the last decade.

Neil, all you said makes lots of sense and I would agree with. Only the Titanium washer and nut brings up a few questions, just like David mentioned. I don't understand the "Titanium has been proven to withstand the heat cycles better than steel nuts do" I probably question that. Not saying you are wrong but I don't understand the theory behind it. Can you get more information on either testing, theory etc.. on this?

[Neil Harvey]

I should have used a different explanation. My bad.

The reason we spec’ed out Titanium nuts and washers was for several reasons.
Titanium has a lower coefficient of expansion than does steel. We have heard about heads nuts coming loose before, but we never get to see the real reasoning. So, when we decided to remake our studs, we chose to use some “just in case and why not factoring”. It was easy as we already have the nuts and washers in house for other applications so why not use them. Also, finding a AN 12pt nut is a lot easier than a metric one. We are limited to thousands at a time when we have them made, so replacing any is not an issue. The more applications we can use them in, the better the investment becomes.

With every kit a small pack of High Pressure Grease goes with them. There is zero galling and we have not had any failures since we started using and selling.
To go along with these studs, we remade our exhaust studs in Titanium and use a Titanium washer and 12pt nut as well. These have the same hex on the end for ease of installation.

Coming soon are our Titanium Case Through bolts with the center dowel and these will also use a Titanium washer and 12pt nut.

These are just a few of the parts for the air cooled 911 engines we have developed. We run out of man hours for everything. The 911 is just one of the Porsche engines we develop parts for. 996 & 997 GT3 and Turbo, 991.1 and 991.2 and now the newer 992. We are also heavy into the new McLaren engines as well. In between we get to rebuild some and do high end machine work for some customers.

[Focker]

Brilliant post.

How refreshing it is to not hear about how 1 product is great and how another product is garbage/monstrosity/doesn't belong in a generator.

[Classic11]

Hello Neil,
I looked at this again yesterday and the nut is right in the air flow (see picture below) and therefore cooled pretty nicely, I doubt it sees temperatures close to core head temperatures just based on its location, so the lower expansion rate of Titanium is likely not a big necessity. I have nothing to back this up but i don't think the material but rather wrong clamp load (high friction coefficient, shape of thread...) are a cause for head bolts to come loose.
But If you already have the titanium washer and nuts for other products available it make total sense to use them here also as they are for sure not worse compared to steel Especially knowing that you cannot order just a few hundred fasteners from a manufacturer.

Very interested in finding out about the Titanium Case Through Bolts you mention, what will be the benefit of using them compared to stock steel?

[Neil Harvey]

Classic11

The main benefit is the center dowel. These are essentially copies of the older race bolts used in the past.

We started building some air cooled engines again and the displacements and strokes are getting bigger and bigger. The case "shifting" needs to be under control and locking the case halves together is really important. What has been done in the past was fitting solid dowels. Nothing new here. Nor is our new bolt. It just makes it easier and solves two issues with one part. The through bolt and the case clamping.

We decided to make them out of Titanium to save weight, the torque value is low and for the same heat control as engine oil passes all around them. Its just been pro active again, if you can why not. We also use more of the same Titanium nuts but with new Titanium stepped washers. We are not going with the original type of central locating concave washers Porsche did in the past. With the machining control we have today, we feel we can use a stepped type washer similar to the stock versions used in then 964 and 993 cases.

[reclino]

When you make the case bolts into locating pins like this do you find the need to line bore the case? Or are the hole locations from.the factory accurate enough?
I know with aircraft parts when a part is restrained with multiple locating features such as this. If there are any pins or holes out of location preloading the solid part to deflect and confirm to this "forced" location the service life of the part is greatly reduced. This causes rapid onset of cracking in the part due to fatigue. I should probably go find a proper reference for this but it's late. Do cases that are dowel pinned or pinned with these race bolts suffer from cracking more than cases that are not?

[winders]

Neil, how much is a set of the 3.6L case through bolts?

[Neil Harvey]

Originally Posted by winders

Neil, how much is a set of the 3.6L case through bolts?

As for cost, I will not show our costs on this forum out of respect to the forum’s owner. If you need the costs etc, best to email.

These bolts are in production now and I expect to have the first 20 sets by mid-March. We have 7 sets accounted for our own projects and I have 5 more on “order” from other customers. We are making 10 sets of each length as the 911 and the later 964/993 use different lengths. These are made on special “swiss type” machines that are very expensive to contract and difficult to get “time on’. I am about to reorder more sets once I have the first sets in hand.

The though holes need to be increased in diameter and reamed to size. This is required only on one side and into the other case half by 0.500”. The nut side of the engine case remains stock. The bolt head side is fitted with a new stepped washer and O ring.

We made a special bar ground to size to locate the case halves perfectly. The main housing bore will need to be correct before doing this process. For those wanting to do their own fitment, I’m hopeful that just the dowel sleeves located at the #1 main and the front sleeve dowel will work as well or a simple sleeve made to locate the front of the case a little tighter than the #8 main sleeve.

We have chosen sizes, so finding the necessary tooling is easy.

[winders]

Nope. Not interested in a product that requires the case to be machined and then can only use that one product. I am not going to be tied to a single solution from a single vendor.

I think I will use the ARP through bolts and get JB Racing to do this to my case instead:



This serves two purposes: case alignment and seals oil passages at the case halves.

This is far better than shuffle pins as shuffle pins weaken the main bearing web.

[Neil Harvey]

Glad you have a solution that you have chosen to go with.
The great thing here is there are more than one solution for builders/assemblers to choose from.

The more companies offer more solutions and parts the better for all.

[Peter M]

Scott,
I'm sure I'm not the only one to think your response above was unnecessarily abrasive. Surely a "thanks but I'm concerned about being able to source bespoked through studs quickly in the future. Consequently I'm might stick with a more conventional method" would have sufficed.

I'm also sure that I'm not the only one here that appreciates hearing from the various vendors and any behaviour that discourages their participation in this forum, especially when their behaviour is exemplary needs to be called out.

Not saying we should pander to everything they say but I think we should be respectful where it is warranted.

[winders]

Peter M,

I'll make you a deal. You don't tell me how to write and I won't tell you how to write.

[911dhutch]

Neil, gracious response........

thank you for the information regarding your engineering rationale and the subsequent high end products you offer our community..

[MST0118]

Scott, thanks for your post about the case work that jb offers. I was just about to pull trigger on getting my 964 case shuffle pinned but now having second thoughts. I saw a similar post on s registry in 2009 where Mike Bruns did similar work while he worked at jb.

It looks very similar to shuffle pins. Do you know enough about process to explain what makes shuffle pins weaken the webbing? First I heard of that. Also, do you know how jb attaches the pins to the case in their method? Interested to learn more. May need to call them for more info.

[winders]

MST0118,

I don't know the details of the process. I brought up the idea of shuffle pinning the case on my race motor with William Knight since we were spinning it to 8000 RPM and might go beyond that. William suggested that we use the JB Racing process instead of shuffle pins if we felt the engine needed it after taking it apart and examining it. He cited compromising main web strength as an issue with shuffle pinning.

We will be rebuilding the engine soon so we will see then what needs to be done.

[Neil Harvey]

Need to make a public apology to my customers who are waiting for these bolts. I have been remiss in keeping you all informed on the situation.

I just got off the phone with one of my customers who has been waiting patiently for us to assembly his engine with these new through bolts. He received an update by reading my recent posts here about the bolts.

I need to do a better job of informing what is going on privately. No excuses here either.

[Walt Fricke]

Re: shuffle pinning.
The machinist I used to use said the issue with shuffle pinning was the register if the hole pairs. He didn't think standard methods (pre-CAM) were accurate enough, and even one pin a bit out of line by a thou or so made splitting the case a pain.

He would bolt the bare case together, remove a through bolt, drill down one of the case holes to the OD of the bushings until he was at the right depth in the other case half. This produced a perfect register for the shuffle bushings.

When done with them all, he made aluminum bushes to install where the outer case was opened to get the hole back to stock there. I don't know if he over-overbored where these outer bushes went - a step to keep them in place. I only figured this out years later by examining the case outsides and noticing what had to be a bush. I can see how a stepped washer could do the same thing.

Care is needed with the depth of some shuffle bushes to avoid compromising oiling holes. Using the 935 type through bolts as shuffle pins looks like it avoids oiling issues, as no inner bushes are needed.

Any competent machinist should be able to install shuffle bushings.

I like Neil's hex ends on his studs, and having a sort of bullet nose avoids the sometimes frustrating, if minor, issue of getting the washer and nut to slip into place down in the hole.