ARP head studs - which way to install

[Walt Fricke]

A discussion of rod bearings got diverted when someone noticed a picture in that discussion of a set of ARP head studs in their package, noticed that these studs have one end radiused to a dome, while the other is cut mostly square. He, joined by some others, opined that the domed end should be installed into the blind threaded hole in the case, because the dome is there to prevent unwanted stresses if the stud is bottomed on installation, and that this is the industry or engineering standard for studs and is the reason for the dome. This was buttressed by a call to an ARP tech, who said that the dome was there to avoid problems if the stud were bottomed in the case.

This precipitated worries from DIY guys who had installed ARPs with the dome out where the head bolts go, who wondered if they had blundered.

Then there were guys like me who assumed that the longer threaded end of the ARPs should go into the case, on the theory that more thread engagement in aluminum is a good thing (in mag it would be even more important), and noted that the threaded length on the domed end is a lot shorter on these studs than it is on the square cut end. Porsche's studs of this era have the same number of threads on each end.

ARP's instructions were then posted, and they don't make any mention of this one way or another.

Me, I rebuilt a motor which came to me with the ARP domes in the heads, and I loved it because the washers and nuts pretty much self centered, like bullet ends on wheel studs.

Those of us in the "put the dome out" camp noted that Porsche cuts both ends square (or, if you want to quibble, not domed and pretty square), and that Henry's Supertechs have no domed ends. In addition, our 911 head studs ought not to be installed so deep that they bottom, because then they will be too short. As long as these studs aren't bottomed, much less torqued when bottomed, it is inconceivable to me that a square end could distort the case, etc., so on that score it can't matter.

The back and forth is found here before someone suggested this topic should have a separate heading: Glyco vs clevite rod bearings - with data. Good point, as the rod bearing question really does matter.

I see the practical issue being is it better mechanically to install the ARPs with the longer threaded end in the case, or the other way around? And the more academic question being is it, indeed, industry best practice to have a domed end on a stud which goes into a blind hole? And if so, did ARP put the dome on the wrong end, because it is hard to imagine they decided that fewer threads were better for the end screwed into the case. I can accept that no one at ARP thought that a bullet nose would make assembly a little bit easier.

[DRACO A5OG]

I am pretty sure it is with the bullet side facing out.

Question I have is do we measure from top of the thread or tip of the bullet end for the 135MM height spec.

[Walt Fricke]

That's an interesting question. With those bullets you don't want to use the barrel nuts, that's for sure.

I think from the top thread would do it. That's what you would do without the dome part. But you could calculate the distance from the spigot top to the cylinder top, and the thickness of that part of the head, and add the washer and nut thickness, and account for the head socketing into the cylinder, and the base gasket and so on.

Or just do a dry assembly in the condition shown (no piston, anyway) in the pictures for just one head, and peek in through the fins and see if a thread or two is sticking above the top of the nut.

The height measurement isn't as exacting as cam timing or bearing clearances, especially after dumping the barrels.

[DRACO A5OG]

Interesting.

I think I will contact ARP, they seem to be very kool kats last time I called. I have to ask them about their torque specifications.

Their instructions state in short: Follow Auto Manufacturer's specifications and Install studs in TWO EQUAL parts to 38 ft lbs.

Does this mean torque at 19 ft lbs then finish with 38 ft lbs?

or

As PAG specifies: 15 ft lbs then 90 degrees

So confused about this???

[Henry Schmidt]

The bullet end is used to assist in the installation of the nut. We suggest a magnetic socket to assist in the installation process on our studs but the bullet tip is a nice addition.
There is no need to measure installed height when using a standard hex or twelve point nut. Installed height is just needed when using stock Porsche Allen nuts.
With ARP just like with the Supertec head studs, you want to install the stud all the way in the back it out a 1/4 turn to relieve stress on the threads.

[m42racer]

Originally Posted by Henry Schmidt

The bullet end is used to assist in the installation of the nut. We suggest a magnetic socket to assist in the installation process on our studs but the bullet tip is a nice addition.
There is no need to measure installed height when using a standard hex or twelve point nut. Installed height is just needed when using stock Porsche Allen nuts.
With ARP just like with the Supertec head studs, you want to install the stud all the way in the back it out a 1/4 turn to relieve stress on the threads.

Without coming off as a """hole, but really, you need to have assistance to install a head washer and nut? If rebuilding one of these simple engines, assistance is required to fit these two parts, I cannot imagine how difficult it must be to fit some of the other fasteners, for some.

All kidding aside, if this is why this feature is added, why isn't the fitted end made with the same dome so the case isn't distorted possibly when the studs are fitted? This is the engineered reason head studs and main studs are made this way.

I don't know of any other head or main studs made for engines that are fitted this "wrong" way around to make the installation of the head fasteners easier.

Seems to me that some of these aftermarket studs were made without knowing this feature is done for this reason.

If ARP have a domed end and have backed up the reason why, maybe it was unknown to them the depth of the case bores. I have no knowledge of this or why, so I cannot speak why they are like this.

In the real world, if you are building a 500+ HP engine, every part used and assembled needs to be carefully inspected and chosen.

I can be fairly sure any of the Porsche studs made by ARP and sold by them to the general public are made as replacements for stock studs. So if the engine you are building makes HP in the 200- 400 HP, I see no reason why the studs would pull out of the case if the dome end was fitted down. If the threads in the case have been prepared correctly, and all other parts in good condition, I would be surprised that even a Turbo engine making upwards of 500HP will pull a stud out of the case.

But you are responsible for assembling the engine, and you have the choice to fit the studs any way you wish. In fact, for a NA engine making 200- 300 HP it will make no difference which way around they are fitted, except the main housing bore issue that could happen.

[gtc]

If you try fitting the ARP head studs both ways, it is readily apparent which way they should be installed.
The length of the threads on the flat end match the depth of the holes in the case. Thread a stud all the way in and then back it off a quarter turn. You will have about a half a thread exposed above the case, and the top of the threads at the other end will be right at the spec for stud height.

[DRACO A5OG]

Spoke with the Tech Support Zach at ARP 805-339-2200.

He apologized about the instructions and clarified the following:

1. Domed (bullet) side is for the NUT. Side without goes into the CASE

2. 38ft lbs is correct, one must split the difference, 1st torque step is 19ft lbs, 2nd final step is 38ft lbs using their included lube. Follow Manufacturer's Sequence of Tightening Order/Pattern.

Sorry, did not bother to ask why they have the domed end in the first place.

[JFairman]

I installed new Mahle 3.3 pistons and cylinders with ARP head studs in mine with red loctite on the case end threads and it's surprising to me that anyone would even consider putting the domed end of the stud with fewer threads on it into the case.

When measuring the 135mm installed stud hight you measure from the case surface to the end of the threads for the nut just below the dome on the end. When doing that you will see all of the threads at the other end threaded into the case.

I did this with the motor in the car with engine tins removed and the back of the motor lowered down about 8 inches on to a jack stand. I do not have an engine stand or yoke or any way to get the motor into my tiny kitchen and into an engine stand so it and the transaxle stayed in the car.
As long as my lower back pain is not unbearable then sitting on the driveway or laying on my side behind or under the car is much easier for me.

The domed end did help make it easy to install the ARP forged steel washer and 12 point ARP nut with the engine in the car.

To install the washer I used one of those small Harbor Freight magnetic tools about the size of a pen or pencil. I stuck the washer to the magnet and inserted it in there and slid it down on the threads on the stud and then stuck a flat blade screwdriver in there to hold the washer in place while pulling the magnet out.
Then I put a little piece of masking tape inside the correct size 12 point socket on an 8" long 3/8" extension to help hold the ARP nut in the socket without falling out.

When I torqued the head nuts I wasn't in a hurry so I did it in 3 steps instead of two for my own satisfaction. Final torque being the 38ft lbs ARP recommended with ARP fastener thread lube on the threads and nut to washer contact surfaces.

Did all this around 2.5 years ago and it all worked out good

[DRACO A5OG]

Outstanding Brother JFairman,

Wow, in the car install, again outstanding.

Yeah, I think ARP assumed you will be installing the studs out of the car and on the stand.

Interesting about the 3 step you took on the torqueing of the nuts.

Very good to hear all went well. BTW why did you change the studs? Preventive Measures or a failure reasons?

[Olsen911]

Walt.

What engine are you making.?

We had some problems with the Arp head stuts and the twin plug heads on 1969-73.

Lower sparks and the domed heads on the Arp studs would touch each other.

Just a head's up.

Cheers - Olsen911 - Tommy Olsen

[JFairman]

Originally Posted by DRACO A5OG

Outstanding Brother JFairman,

Wow, in the car install, again outstanding.

Yeah, I think ARP assumed you will be installing the studs out of the car and on the stand.

Interesting about the 3 step you took on the torqueing of the nuts.

Very good to hear all went well. BTW why did you change the studs? Preventive Measures or a failure reasons?

Compression was a little low in number 6 and all the exhaust valve guides were really worn out. This is in an '87 930 and it seems they use up exhaust valve guides quicker than other motors.

Here's a pic I took when putting it back together with new Mahle 3.3 pistons and cylinders from a sealed box and resized connecting rods with new bearings at each end.


The ARP studs look nice and the red stuff is Redline assembly lube I put on the piston skirts to help lubricate them during initial start up. Not needed but I did it and only motor oil is on the piston rings.
The blue stuff is hylomar gasket sealant I put on new .25mm cylinder base gaskets. A little more than needed but I didn't want any oil seepage there and any squeeze out cleans up easily with lacquer thinner on a rag. Then it looks real nice when done.
I balanced all the pistons down to 1/10 of a gram by grinding some metal out of the inside ends of the wrist pins with a die grinder like I've seen done before.
The aluminum foil and wadded up paper towels are there to keep anything (like a wrist pin circlip) from flying into the case while doing this.

[DRACO A5OG]

Interesting choice on the Hylomar Blue, may I ask why?

I am digging the foil and paper towel trick .

Yes, those studs look great!

Do you happen to know the valve guide material?

[JFairman]

I used Hylomar because I like it. It's similar to Curil-T but a little different.
It can be hard to find but this place has it for 11.95 shipped.
Hylomar Universal Blue Gasket Sealer - 100 Gm Tube | eBay

I don't know what kind of valve guides were in my car when I got it. They looked like the usual phosphor bronze alloy valve guides

[DRACO A5OG]

Sowwy Master Walt for the HiJack. I will stop now :-(

So I think it is pretty certain Dome goes towards the outside of the case. Love to see anyone try the other way and see how that worked out. I guess long as one does not go Double Plug set up.

[Walt Fricke]

Tommy - the ARPs on the 2.8 (2.7 heads twin plugged at 14mm) are a bit tight for getting a wrench on the nuts. But do-able. On my other twin plugged motor, a 2.7, the lower plugs are 12mm to reduce the interference issues, and I had to bevel the barrel nut tops before I realized the reduced head flange nuts probably would help there. My twin plugged 2.8SS with 3.2 heads has none of these issues.

But I think there is no Porsche spec for after market twin plugging, so I anticipate some variation from machine shop to machine shop, as each is likely to have its favorite and tried and true setup.

Does anyone note the irony that one ARP guy says dome goes in, and another says it goes out?

But when I went to build an engine from the ground up, so to speak, I got Henry's studs. Wish he had those domes, but not a deal killer.

[DRACO A5OG]

Originally Posted by Walt Fricke

Does anyone note the irony that one ARP guy says dome goes in, and another says it goes out?

That is crazy, that is why I asked for the head tech's name.

[chris_seven]

Some of the 'advice' that ARP provide does seem worrying and that they would suggest fitting the 'domed' end into the blind hole makes me smile

In their general advice they also make statements that I fond difficult to accept.


Do the head studs only go in hand, or finger tight?

Yes, cylinder head studs are installed only hand tight. Other than the use of an allen wrench on the hex broached into the end of the stud (to ease installation, not to apply torque), use no tools to seat them in the block. However, it is extremely important to ensure that the studs are fully bottomed out in the hole in the block and not hung up on damaged or corroded threads in the block preventing the stud from being fully seated. This is often indicated when the stud threads extend past the deck surface.

The idea of bottoming a stud into the blind end of a threaded hole cannot be good practice.

The final threads in any blind hole are very unlikely to form correctly and two problems can occur.

The first is that the stud can misalign in the thread clearance and this means it may not pull down completely square and can cause head seating problems.

I would say this is unlikely with a 911 as the stud is fairly long and quite thin so it will bend quite easily but short large diameter studs could cause real issues.

It used to be common practise in old motorcycle engines to drop a small ball bearing into the bottom of stud holes to prevent this problem.

Tightening a stud to the bottom of a hole can also cause failures in the base material.

The forces created due to the poorly formed thread can cause cracks when the stud is tightened to 'bottom' out the thread but this would only tend to occur with cast iron parts and as ARP also say not to apply torque I am not sure how both objectives can be achieved.

It has become common practice to use studs than a 'base seating' feature' which has been promoted by Cosworth.

They state that this is to distribute load evenly into the stud rather than the thread and this needs some qualification.

There are many studs now being made with this feature which I believe only has one important characteristic.

From the measurements we have made virtually all aftermarket head studs are made to a an ASTM A2 class of fit. (Equivalent to 6g for ISO Standards)

This is a 'commercial standard and is not as good as the stock steel stud supplied by Porsche which are measurably better than this specification.

This means that the alignment of genuine Porsche studs is better than would be obtained when using an aftermarket component.

If we add to that the fact that many individuals clean case threads using a tap rather than a thread chaser than the quality of fit and hence alignment will only deteriorate.

We now only clean threads using a chaser- which is made from an old stud.

We now have our own thread rolling machine and we are trying to find a way to improve the class of fit of stud by carefully controlling the size of the blank and see if the can obtain the same fit as Porsche.

At the moment our new studs do have a dog point and we do tighten then into the case but only to a very low torque.

We do this to optimise alignment before the thread locker sets.

[Walt Fricke]

Chris - What is a dog point? I can make myself believe that the Porsche stock older studs have a slight conical end, maybe about half a thread width?

Are your studs made over length and you are confident that they don't have to be separately set for matching height off the deck?

What do you suppose the domed or bullet end on ARP's Porsche head studs might be for - at least as a general feature of studs threaded into blind holes?

The Supertec stud installation instructions say to screw the stud in until it bottoms, and then back it out a bit (I forget the specification for this), but of course until the height off the case is correct. No chance of installing these bottomed if you follow instructions.

The guys who supposed that the dome end was meant to be screwed into the case sounded like they had training as mechanics (most of us are DIY), and might know about engines other than Porsches. I know there are lots of people who know more about this kind of thing than I do, so I'm not inclined to dismiss their contributions. What might be behind their views?

I think that in auto mechanics, as in various other fields, sometimes a practice which made sense once no longer matters. My favorite example is bleeding brakes. We are told to bleed the caliper farthest from the master cylinder, and work our way to the caliper with the shortest line. For 911s this always means start with the rear calipers first. Since the advent of the tandem MC, there can be no earthly reason to do the rears before the fronts, as they are two separate systems, just as a dual MC would be. I'm unsure how bleeding a shorter line first would allow a bubble to be introduced back into it when the longer line was bled, but there might be something to that. Not enough for me to bother - I tend to bleed the side I have up for tire changing first, and then the other side, whichever one it is.

[chris_seven]

My amusement is that ARP would suggest this not that people who, like me, grew up in the days of installing ball bearings in Norton and Velocette Engines may make this assumption.

I have always thought that the domed end on an ARP Stud is to 'catch' the nut. ARP seem to supply their studs with a 12 point Flange Nut and the dome makes it a little easier to drop into place.

Fitting the domed end into the case as a 'base feature' suggested by Cosworth would mean that the radius at the bottom of the blind hole would need to match the tip on the end of the stud or it could push sideways.

Cosworth tend to use a 'square' end about 6mm diameter which could also be a problem if the end of the blind hole does have a radius.



Stud with Dog Point

We have used a traditional 'dog point' which has a small flat on the end of a cone which will tend to seat even into a shallow radius.

We have checked a number of studs and they do line up quite square to the engine case and the small torque we use does allow us to achieve this before the Loctite sets. We also use Loctite 640 which is quite 'slow'.

We supply a very similar 12 point flange nut to that used by Henry - it is an M10 x 1.25 and is a Porsche 928 Con Rod Nut. This means that the installed length is not very important.

We have also measured the blind hole depth distribution on early sand cast cases, magnesium cases of 2 x generations and later Alusil cases both Carrera 3 and SC and they were all within 0.35mm of the shortest length but did not describe a normal distribution.

we have made the thread length at he head end slightly longer os we will have no issue with washer position.