ARP Head Stud Installation - Instructions vs. Reality

[Edunit]

ARP info - perfect!

[JFairman]

some more ARP info...

[The Watson]

I had an interesting day yesterday installing the Supertec stud kit. My case has inserts that were very clean and case was just machined by Ollies. The studs screwed in about through 2/3 of the stud thred with no resistance - even a bit wobbly. Then it became a very tight fit. The fellow at Supertec (wasn't Henry) on the phone had not run into this situation and recommended I just insert, with a ratchet, until almost all the threads were inserted. That meant only about half or three quarters of a rotation of the stud once there was any tension. The holes were certainly deeper than the inserts so I was not bottoming out. I didn't walk away with a real confident feeling about all of this but hopefully they will be ok, especially if hand tightening is all that is really necessary. Thoughts anyone?

[Lapkritis]

Could be air compressing beneath the stud. Sometimes letting it rest overnight will release the pressure and they'll turn a bit easier.

[Gordo2]

Originally Posted by The Watson

...Thoughts anyone?

Yep -

You are describing the exact situation that promted me to start this thread.

Gordo

[chris_seven]

I you consider a metric thread form the crest is always cut away and the root is rounded so there will always be a small gap. Air is also extremely compressible so I am not sure that air compression can be the cause.

This issue being described is almost certainly a result of the Fit of the two threads.

Depending on what has been done to the case threads there could be issues with the fit of an aftermarket stud.

It is quite difficult to measure the thread in the case without buying a few expensive gauges but it is relatively easy to gauge a stud.

I am sure that most studs are well made but as there is no published data available so it is hard to make a judgement when there seems to be a problem.

The Class of a thread is quite difficult to explain and I am not sure I have a complete handle on it yet as there can be variations in pitch, pitch diameter, maximum and minimum diameters and they will all have some impact on how easy it is to install a stud and subsequently how much load it can support.

I hope to have a detailed model which looks at the impact of case thread and stud thread tolerances in a couple of weeks time and I plan to write a short note on the subject.

From some basic measurements I think that there is around 27mm of well formed thread in the holes in the engine case. The hole depth is between 34.5 and 35mm and the base of the hole is rounded.

If you try to insert a stud for longer than the 27mm distance you will run into some poorly formed threads and tightening into this regions is a little undesirable but unlikely to be fatal.


Until we started making detailed measurements I has always assumed that 'extra thread' on the case end of the stud was a good idea but as we have started gathering data for an FEA Model, I am not quite so convinced.

If this is not the problem you are encountering then it could be that the thread on the stud may be a slight mismatch to the thread in the case.

The fact the thread may seem 'wobbly' with just a few threads engaged is a red herring as the mismatch will become more apparent the more threads engage.

During the last few weeks, however, I have come to the conclusion that studs with a 'base seating' feature are a good idea and once we have our model completed we hope to substantiate this belief with some good design data and design a suitable stud with all of the thread class data provided.

[DSPTurtle]

Love this group! Can't wait to see the details on the FEA model.
The Matco tool truck carries a relatively inexpensive thread chaser. I think I bought the whole set, m6-m10, male and female for under $30. Most well used tools in my box.

[The Watson]

Was still unsure about my installation so I went a pulled one of the Supertec studs to compare it to the stock stud. The Supertec studs threaded area was a tiny bit narrower than the stock stud. This could account for some of the wobble I was seeing.

Stock Stud:


Supertec Stud:


However both had a bit of wobble when inserted into a new 10x1.5 nut, so I guess that aspect is standard.

I was also concerned about the amount of thread still showing after my install>


But then I compared the threaded portion on each of the studs and the Supertec studs have a longer thread area (right end in photo below). Without this extra thread area I would have been pretty close to having no threads showing if using a stock stud.



So I decided to re-blue-loctite the removed stud and call it a day. If anyone thinks I am making a mistake I'd love to know.

Gordo, I hope I haven't hi-jacked your thread. Just trying to add more discussion to the helpful thread you started....

[Henry Schmidt]

Originally Posted by The Watson

I had an interesting day yesterday installing the Supertec stud kit. My case has inserts that were very clean and case was just machined by Ollies. The studs screwed in about through 2/3 of the stud thred with no resistance - even a bit wobbly. Then it became a very tight fit. The fellow at Supertec (wasn't Henry) on the phone had not run into this situation and recommended I just insert, with a ratchet, until almost all the threads were inserted. That meant only about half or three quarters of a rotation of the stud once there was any tension. The holes were certainly deeper than the inserts so I was not bottoming out. I didn't walk away with a real confident feeling about all of this but hopefully they will be ok, especially if hand tightening is all that is really necessary. Thoughts anyone?

I just noticed this thread so I'll respond to the question the best I can.
The gentleman who answered your question Terry (my machinist) is not an engine builder.
He was trying to help but your insistence prompted him to generalize without completely understanding your specific issue.
The issue is not with the stud. The issue is with the insert.
Generally after installation you need to clean the threads with a forming tap. This type of tap forms the threads to a more consistent dimension than the cutting tap that was originally used to manufacture the insert. Also quite often, the tool used to install the insert is not threaded into the insert completely and the threads end up inconsistent towards the bottom.
We offer the forming tap to any customer experiencing this type of issue.

[The Watson]

Henry -

I would like to obtain this forming tap. The issue you describe with the inconsistent threads at the bottom sounds exactly like what I have encountered. I will contact you separately.

[Jcslocum]

I looked this up just to be able to know what Henry is referring to:

Thread forming taps are designed to displace material by pressure rather than cutting the material away. Also known as cold forming taps, they have a fluteless design which is well-suited for blind holes since there are no chips to evacuate. Tool life can be three to twenty times longer than traditional taps, and thread forming taps can be run at faster spindle speeds for higher production rates at less cost per hole. Suitable for use in ductile materials without chips, such as aluminum, brass, copper and zinc - generally, materials which provide a continuous chip when drilling work well with these cold forming taps. Available in standard and Metric models.

[Henry Schmidt]

In response to Chris' query about thread class, the Supertec head studs are built to a Class 2A using the ASME/ANSI B1.3-2007 Screw Thread Gaging Systems.

[chris_seven]

Henry,

Thanks - I guess this is equivalent to a 6g in Metric speak which is classed as a 'medium' or commercial fit and from the number of studs you have supplied clearly good enough.

We have gauged a number of 'old' steel studs and the are a 'Close' fit and better than 6g.

We have also tried some Porsche supplied new steel studs which will fit though a 6g No-Go gauge so are a lower class of fit but I don't want to buy a set of gauges to measure a 'loose' fit.

[Gordo2]

Originally Posted by The Watson

Gordo, I hope I haven't hi-jacked your thread. Just trying to add more discussion to the helpful thread you started....

Good to go Chuck,

Glad you jumped in and contributed. Saving others from similar head scratching in the future - that's what it's all about.

Good luck,

Gordo

[JohnJL]

Originally Posted by Henry Schmidt

In response to Chris' query about thread class, the Supertec head studs are built to a Class 2A using the ASME/ANSI B1.3-2007 Screw Thread Gaging Systems.

Holy poo Henry. That was a 10 year old post!

[JohnJL]

Error

[triguy]

The Watson, How did this turn out for you. I have the same situation. I have case savers installed in my 2.7 and when I put the supertec head studs in they are quite loose. I believe both parts to be ok but do not fit together properly due to tolerances.

Thanks Neil

[The Watson]

Neil. I did use Henry's thread shaper to extend good threads all the way through the case saver. They were still somewhat loose but tight after blue loctite set up. I am pretty comfortable with it due to the clamping force being what secures everything but time will tell ;-)

[triguy]

Thanks for the information. I thinks the studs will function very well, My main concern is I could not get them to stay tight even with Loctite and they would loosen off.