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ARP head studs
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Author:  LMWatBullRun [ Mon Feb 27, 2012 4:53 pm ]
Post subject:  ARP head studs

Can anyone provide the diameter, thread pitch and length of the head bolts used in the 2.8 CRD? I have not taken mine apart to that degree yet, and I have just decided that I am going to get ARP studs for this motor.

A number of other diesels have aluminum heads, and almost without exception the additional clamping force and superior torque control that the ARP studs provide help prevent/correct head warping and allow higher boost pressures. The stories I have read here about the aftermath of overheating the engine sound a great deal like those I have read about TDIs and Volvo TDs like my 760. A set of ARP studs will probably run a couple/ three hundred bucks or so, but next to the PITA factor of head warping/hg failure I think it is worth it.

ARP does not list a set for our 2.8 VM, but if I get the bolt specs, I will post the ARP part numbers when I get them.

Author:  racertracer [ Mon Feb 27, 2012 6:14 pm ]
Post subject:  Re: ARP head studs

LMWatBullRun wrote:
Can anyone provide the diameter, thread pitch and length of the head bolts used in the 2.8 CRD? I have not taken mine apart to that degree yet, and I have just decided that I am going to get ARP studs for this motor.

A number of other diesels have aluminum heads, and almost without exception the additional clamping force and superior torque control that the ARP studs provide help prevent/correct head warping and allow higher boost pressures. The stories I have read here about the aftermath of overheating the engine sound a great deal like those I have read about TDIs and Volvo TDs like my 760. A set of ARP studs will probably run a couple/ three hundred bucks or so, but next to the PITA factor of head warping/hg failure I think it is worth it.

ARP does not list a set for our 2.8 VM, but if I get the bolt specs, I will post the ARP part numbers when I get them.



I'll look for mine and let you know.

Author:  LMWatBullRun [ Mon Feb 27, 2012 10:32 pm ]
Post subject:  Re: ARP head studs

racertracer wrote:
LMWatBullRun wrote:
Can anyone provide the diameter, thread pitch and length of the head bolts used in the 2.8 CRD? I have not taken mine apart to that degree yet, and I have just decided that I am going to get ARP studs for this motor.

<snippo>
ARP does not list a set for our 2.8 VM, but if I get the bolt specs, I will post the ARP part numbers when I get them.



I'll look for mine and let you know.


Thanks, RacerTracer. I suspect that ARP is going to sell quite a few sets of these to folks here.

Author:  racertracer [ Mon Feb 27, 2012 10:43 pm ]
Post subject:  Re: ARP head studs

Well I hope i will never need to replace mine again.

Author:  LMWatBullRun [ Mon Feb 27, 2012 10:47 pm ]
Post subject:  Re: ARP head studs

The thing about the ARP studs is that they hold the head so much tighter. I know of one fellow who reportedly has run 45 pounds of boost on a D24T, designed for 12 pounds, and with ARP studs has had no trouble :!: I know a lot of TDI members swear by them, as they reduce HG problems to virtually nothing.

Author:  msilbernagel [ Mon Feb 27, 2012 11:22 pm ]
Post subject:  Re: ARP head studs

Perhaps someone who's pulled a factory head bolt can send them one along with the tightening specs from the FSM.

Since they're not re-usable...

That'll help them get it right.

Part of the reason for choosing torque-to-yield is that it results in smaller/lighter bolts and reduced expense.

Be interesting to see if ARP can fit a reusable bolt in the same space?

Mark

Author:  warp2diesel [ Tue Feb 28, 2012 12:28 am ]
Post subject:  Re: ARP head studs

The thermal expansion rate of aluminum is twice that of steel. The ARP studs look like they are turned down so they stretch when the head expands and go back to the original length when the head cools down. By having the head bolts or studs elongate with in the elastic limit, the head gasket lasts longer. That is why torque to yield bolts/studs work better.
If the stock 2.8L CRD head bolts are like the VW pre-TDI head bolts with threads going all the way to the head, the studs should have a turned down section that is about the same as the root diameter of the head bolt (assuming the same alloy for both the bolts and studs in theory). If the head bolts are turned down, the studs should be about the same. If the studs are turned down to a larger diameter than the head bolts, the head gasket may get trashed because the studs will not yield enough.
If ARP is willing to engineer a set of studs for the 2.8L CRD, they should be great. Even a Wild @$$ Guess from ARP would be better than just matching up bolt to stud sizes, it is not that simple. If you try to only match up the length, diameter, and thread pitch, you are gambling on your own dime. So good luck, you will need it.

Author:  LMWatBullRun [ Tue Feb 28, 2012 2:39 pm ]
Post subject:  Re: ARP head studs

Arp studs clamp tighter for a number of reasons, some of which are:

-the threads on nuts and studs are precisely machined to spec, either precision machined or ground, or both.

-the bearing faces on the nuts are exactly perpendicular to the thread axis.

both of these factors mean that nut torque translates to compression more repeatably.

-the steel used is high strength high temp alloy, which has a much higher yield point than other steels. This means that when the steel stretches under load, it never is stressed past the yield point and always returns to the starting compressive preload induced by the initial torque. the precise machining of the threads means that there are no high spots along the block thread helix to yield when overstressed in service.

Bottom line, they work. The fact that they facilitate head removal and replacement is just icing on the cake; I have heard that a number of TDI club members have replaced their bolts with ARP studs one by one just to allow more boost.

Author:  warp2diesel [ Thu Mar 01, 2012 9:33 pm ]
Post subject:  Re: ARP head studs

LMWatBullRun wrote:
Arp studs clamp tighter for a number of reasons, some of which are:

-the threads on nuts and studs are precisely machined to spec, either precision machined or ground, or both.

-the bearing faces on the nuts are exactly perpendicular to the thread axis.

both of these factors mean that nut torque translates to compression more repeatably.

-the steel used is high strength high temp alloy, which has a much higher yield point than other steels. This means that when the steel stretches under load, it never is stressed past the yield point and always returns to the starting compressive preload induced by the initial torque. the precise machining of the threads means that there are no high spots along the breeze helix to yield when overstressed in service.

Bottom line, they work. The fact that they facilitate head removal and replacement is just icing on the cake; I have heard that a number of TDI club members have replaced their bolts with ARP studs one by one just to allow more boost.


I Read through their catalog and their quality exceeds the Bean Counter Engineering of the Auto industry, no dispute. Their Carefully Engineered Studs for the TDIs that work great. If they Engineered studs for the CRD, they would work great as well. My point is, even their Wild @$$ Guess is better than trying to pick out fasteners from their catalog on your own with out their input.
A head bolt/stud for an aluminum head has to yield when torqued but not exceed the elastic limit. If the head bolt/stud does not yield when the head heats up the head gasket has yield to make up the difference and when it wears out from being over stressed the head gasket fails. ARP plugs all of this into their calculations to design the stud for the application, that is why they work so well.

Author:  geordi [ Fri Mar 02, 2012 1:17 am ]
Post subject:  Re: ARP head studs

If somebody can confirm a way to identify which bolts are the head bolts... I will happily donate one from my collection of used engine parts. I've got a couple bags of assorted bolts, some of which are BIG honkin things. I'm guessing the big ones would be the winners... But I wasn't there for the teardown.

Racer / Sam / Mark... Somebody who has been into the top end - is there any way to definitively ID these things? Distinctive markings? Special head size / shape?

Let me know. If there is a way to change the bolts to studs without pulling the entire top end apart, I would be ALL ABOUT swapping to ARP studs. I did it that way on my Jetta TDI, one bolt at a time and the head gasket never moved. I do think the studs helped compression too, b/c the engine started right up after doing it, when it had an internal problem in the pump that was making it VERY hard to start. After getting the pump fixed, it would start almost by looking at it funny, and ran like it was brand new.

Author:  racertracer [ Fri Mar 02, 2012 1:22 am ]
Post subject:  Re: ARP head studs

I'll find the bolts in my spare parts bin this weekend and see about sending them off to ARP.

From what I can understand the block bolt holes would have to be re-tapped to accept the new ARP bolt size.

Author:  LMWatBullRun [ Fri Mar 02, 2012 9:38 am ]
Post subject:  Re: ARP head studs

racertracer wrote:
I'll find the bolts in my spare parts bin this weekend and see about sending them off to ARP.

From what I can understand the block bolt holes would have to be re-tapped to accept the new ARP bolt size.


Not sure about that either way. The holes in the block for the D24 did not have to be machined as long as they were the 12 MM bolts.

Author:  LMWatBullRun [ Fri Mar 02, 2012 9:49 am ]
Post subject:  Re: ARP head studs

warp2diesel wrote:

I Read through their catalog and their quality exceeds the Bean Counter Engineering of the Auto industry, no dispute. Their Carefully Engineered Studs for the TDIs that work great. If they Engineered studs for the CRD, they would work great as well. My point is, even their Wild @$$ Guess is better than trying to pick out fasteners from their catalog on your own with out their input.
A head bolt/stud for an aluminum head has to yield when torqued but not exceed the elastic limit. If the head bolt/stud does not yield when the head heats up the head gasket has yield to make up the difference and when it wears out from being over stressed the head gasket fails. ARP plugs all of this into their calculations to design the stud for the application, that is why they work so well.


I wasn't planning on picking a bolt by myself, but I am not going to pull my head just to get the required measurements. ARP has a rather detailed series of questions that they ask about hole depth, diameter, thread pitch, etc. etc. that you need to answer so that they can do the design. I knew that others had replaced heads and gaskets and was hoping to jumpstart the process by getting the bolts specs to start.

If they needed more thread engagement in the block for stud loads then I could ask for more input regarding hole depth. My hope was that just as with the D24T that the stock thread engagement would be sufficient for the increased load of the stud, but I am going to let ARP do the design. If you or RT are going to engage in talks with ARP, and you have all of that information, great! If you are going to do that, looking at their questionnaire is recommended, because they are going to want that information. been down that road twice, once with the D24T and once with a Honda Civic.

Author:  geordi [ Fri Mar 02, 2012 12:57 pm ]
Post subject:  Re: ARP head studs

At least on the Jetta TDI, the head did not need to be retapped for their studs. You simply twist it in finger tight, then go to town on the nut on top following their torque specs. To do the job without removing the head, there is a specific clamping procedure to follow, applying torque in (IIRC) 3 passes over each nut.

Based on the stock bolt itself, I don't see where they would have a problem matching the number of threads, but I know they probably want to increase the thread count IN the block as a means of increasing the clamping force. Don't forget to tell them that you are threading the stud into an iron block, not an aluminum head... The holding power of those threads should be a lot higher, iron can put up with a LOT of shear force.

Author:  warp2diesel [ Fri Mar 02, 2012 5:14 pm ]
Post subject:  Re: ARP head studs

Here is a photo of the CRD head posted by another member with the cam shafts and the integral intake removed.
Image

As you can see, the integral intake and the cams will need to be removed to do any retorquing of the head. You will want to point this out to ARP so they can make a good recommendation. Having to retorque with a warm engine or turning an extra fraction of a turn after the engine is assembled is not an easy option with the 2.8L VM CRD. Also let them know how much room there is under the integral manifold that houses the cam shafts so the studs and nuts will clear. If I were doing the fit, I would set the integral manifold onto the head with out the cams to make sure it seats properly and did not crash into the studs or nuts.

A historical example of the need to have head studs stretch to keep the cylinder heads sealed up is the old VW air cooled engine. When straight 10 mm studs were used, the jugs dug into the heads and trashed them out causing the heads to leak. When the 8 mm studs were used, the studs stretched and the heads did not leak. I would bet a cup of coffee that the Gents at ARP learned this historical factoid early in their life either from working on VW air cooled engines, Deutz diesel engines, or air craft engines.

Good luck!

Author:  racertracer [ Fri Mar 02, 2012 5:37 pm ]
Post subject:  Re: ARP head studs

I called VM Motori to inquire about the information we need for the development of the ARP bolts.

The gentleman I spoke with said to forward him an email with what we are looking for and that he will respond.

I downloaded the info sheet from the ARP web site and forwarded it to VM.

I believe we desire studs instead of bolts.... any opinions on that question?

I'll keep you all posted as soon as I get a response.

Author:  LMWatBullRun [ Fri Mar 02, 2012 6:19 pm ]
Post subject:  Re: ARP head studs

racertracer wrote:
I called VM Motori to inquire about the information we need for the development of the ARP bolts.

The gentleman I spoke with said to forward him an email with what we need and that he will respond.

I downloaded the info sheet from the ARP web site and forwarded it to VM.

I believe we desire studs instead of bolts.... any opinions on that question?

I'll keep you all posted as soon as I get a response.

Studs.

Author:  papaindigo [ Fri Mar 02, 2012 6:28 pm ]
Post subject:  Re: ARP head studs

X2 plus any tips VM could provide on how to do an install. It sure would be nice to be able to do the install 1 at a time without removal of the head as geordi notes can be done on a TDI.

Author:  racertracer [ Fri Mar 02, 2012 6:56 pm ]
Post subject:  Re: ARP head studs

I will see what VM says about that.... I hope they can give us some advice.

The ARP tech said that replacing the head bolts one by one has been done in the past with success but there is no guarantee that the head gasket will not leak.

He said that in his thirty years at ARP and hearing stories from people who have done it that way in the past, more often than not the cylinder head gasket leaked, he said that if you're into the engine that far it would be silly not to go all the way.

Furthermore, he said that if the bolts are not custom made and are picked from readymade off the shelf stock, the cost would be approximately $375.00, if instead the bolts are custom made then the cost would be considerably more, approx. $1000.00 with an 8 to 12 week lead time.

Author:  LMWatBullRun [ Sat Mar 03, 2012 8:44 am ]
Post subject:  Re: ARP head studs

I haven't looked at the integral intake manifold to see whether there is any way to get at the head bolts without removing the integral manifold, but I don't see how you could. (The manual sketches are only as detailed as they think they need to be, so I could not tell by reading the book) The seating surfaces of the manifold appear to wrap all the way around all the head bolts. If I were an engineer at VM Motori, I would probably be very interested in a better solution to the head sealing issues presented by that design.

If you look at the location and the tightening pattern for the head bolts, it sure looks to me as though the 10 inner bolts are doing most of the work, while the 8 outboard bolts are there mostly to seal the fluids. My bet is that the problems inherent in TTY head bolts are only magnified by the differential temperatures and stresses those head bolts encounter. I'd love to see the computer stress simulation over a combustion cycle for that motor, but even without looking at that it does not surprise me that these engines are so sensitive to overheating or coolant loss.

Question to those of you who have done HG replacements: Do the stock headbolts come with precision ground washers?

Followup: Did any of you try to lap the block bolt threads in any way before installing the new bolts?

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