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Hardening steel
mark chandler - 28/1/19 at 10:06 PM

An interesting one for the collective, I want studs for holding down my jaguar AJ16 engine head, these are not made by anyone and the factory uses stretch bolts.

The block has 7/16 UNC threads, these are ideal for aluminium not stretch bolts as much to aggressive and you cannot buy studs off the shelf.

I purchased a length of 7/16 en24t, cut my threads, UNC for the block & UNF fir the nuts - I have a set of ARP nuts on there way

So my first attempt, heated the stud to 840 degrees for 1/2 hour then quenched in engine oil, it was not as hard as I expected but definitely harder than when delivered then tempered 600 degrees for an hour and left to air cool. From a quick hacksaw test still as hard as when initially quenched.

To test I wound on a HSS nut so it stood proud of the thread, popped into my press and just on 5 tons the threads failed, I thought this was pretty good but it's not enough

So my question, was my heat treat correct, should I have gone higher than 840 degrees (it was glowing a nice red), or was my oil wrong and failed to cool fast enough? This is new 10/40 semi synthetic, maybe it's to insulating and a pint of nut oil from the suoermarket would have been more successful, more conductive?

Anyone else done this, I know rolling threads is stronger but not on my budget, threads were single point cut on my lathe, I went for an engineers fit, no slop so happy I had a good fit.

Cheers

Mark

[Edited on 28/1/19 by mark chandler]


melly-g - 28/1/19 at 10:19 PM

I'm by no way an expert on this but you wouldn't want to use synthetic oil for this would you?


mark chandler - 28/1/19 at 10:45 PM

I just used what was lying around, may have been a mistake this is a test pieces so not an issue at this stage.


loggyboy - 29/1/19 at 12:13 AM

Why not use water?


gremlin1234 - 29/1/19 at 12:17 AM

why harden the studs, when they will shortly be subjected to a lot of heat/ cool cycles, which will probably soften them again?


Angel Acevedo - 29/1/19 at 12:19 AM

I thought cut threads are a no-no on high strenght fasteners....

I may be wrong but threads on high strenght fasteners are rolled and not cut..


AA


mark chandler - 29/1/19 at 07:18 AM

Rolled threads are stronger, I do not have a thread rolling machine.

My car blew it's head gasket @385bhp, I am looking to add 40hp more with cam and head work so have to move to studs, yes I could commission rolled threads but if I can single point cut tight threads and harden if strong enough this costs my £30, not £320, I need 16 of them.

Hardening/softening is in the 700-800 degrees range, In the car maybe 120 degrees so no softening, you have to temper of they may crack.

My first attempt failed at 5 tons when pressing the thread through the nut.

[Edited on 29/1/19 by mark chandler]


CNHSS1 - 29/1/19 at 07:20 AM

ARP will make any stud, any length/thread. You can get a form from them, fill it in and presto.

DIY studs seems a little bit and miss especially if you've had an issue already


Mr Whippy - 29/1/19 at 07:23 AM

While I commend your wish to experiment your are doing so with studs to hold down your cylinder head... just think what could happen if you don't get it right.

1) Studs could snap in the block possibly wreaking the block trying to get them back out

2) They snap and the head ends up distorted

3) They snap at a later date (who checks these regularly?) leading to a breakdown, blown head gasket, damage and the car needs recovered

You also don't say why you want to use studs rather than the normal bolts which are neither difficult to obtain or expensive to buy. Why do you want to fit DIY homemade alternatives instead of using certified reliable parts where the consequences of failure are so serious?


JAG - 29/1/19 at 09:32 AM

First thing to do is make some more Studs, without any attempt at Hardening or Tempering, and re-run your thread strength test.

Compare that result with your previous result for the hardened and tempered studs.

At least you now know how much you have or have not improved things.


Ten go back to your hardening attempt;

You're heating the Steel to dis-solve the current chrystaline structure and while its dis-solved you cool it rapidly to encourage the Steel structure to form Martensite. If you cool it very rapidly (water quench) you will create more Martensite but with the risk of over hardening the structure and generating cracks. That's why Oil is used - to avoid damaging the work piece by cracking. Grade's of Oil etc.... are less important.

I'd read up on the internet - there are lot's of academic research papers out there that contain better and more detailed stuff than I remember from University.

PS; Good question above - why Studs and not Bolts? Thread engagement is king with high strength joints and Studs with Nuts have less thread engagement than Bolts into threaded castings etc....

[Edited on 29/1/19 by JAG]


rusty nuts - 29/1/19 at 11:31 AM

My thoughts were that with a stud and nuts there are two sets of threads which are potentially weak points? Are any of the older jag head studs the correct dimensions and of use if you do decide on studs?


mark chandler - 29/1/19 at 01:17 PM

Jaguar kept aluminium pitch, UNC which means that bolts 70% of the torque is twisting the bolt, 30% clamping, also high end is always studs as you get far better clamping, that’s why ARP exist!

My engine is 6 cylinders 3.2 running 12psi boost so a lot of force, the fire rings on no1 burnt through 1 January so while it’s in bits I am improving stuff.

So UNF nuts on studs will not twist the stud and the fine pitch gets a lot more clamping for my torque wrench to apply fit the same given pull. It’s also a lot more accurate than stretch bolts for loading.

Stretch bolts are a manufacturer cost saving, fine for low performance engines, if I cannot make myself I will bite the rolled threads route.

We are locost after all and I prefer to make before buy, my little car is scratch built and I have a lathe and mill to make stuff

Last year I started to cast aluminium so made a calor gas bottle electric furnace


JAG - 29/1/19 at 02:04 PM

quote:

We are locost after all and I prefer to make before buy, my little car is scratch built and I have a lathe and mill to make stuff



I applaud you and would encourage this attitude all the way

Holding your cylinder head on your engine is a simple Engineering problem. You 'simply' need more tensile load in all of the studs/bolts than force from your exploding fuel pressure multiplied by your cylinder area.

To get that tensile load you need lot's of thread engagement - which equates to metal area under Shear load.

Do the maths - see how much thread engagement you have, calculate the area of the joint under Shear load and then see if the material properties suggest the joint will hold.

As for this comment....

quote:

Stretch bolts are a manufacturer cost saving, fine for low performance engines



It's not true.

I am personally responsible for Bolted joints that hold the Brake Calipers onto a certain Vehicle Manufacturers cars. We use tightening with "Torque and Angle" (or 'Stretch' Bolts) because that produces the maximum tensile load in the joint and, when done correctly, ensures the joint is holding the maximum load it is capable of holding and won't come undone through vibration etc... We have special tools on the production line to apply the torque and subsequent angle and we record the data from every single bolt for Quality Control. It isn't cheaper and it is more complicated and difficult to get right.

[Edited on 29/1/19 by JAG]


Angel Acevedo - 29/1/19 at 03:59 PM

Pros and cons are stated.
in the end, it all boils down to the same, if you are well informed and take a decision based on available information and the amount of risk you are willing to accept is OK.
Everybody has a different threshold to each variable...
I am very interested on your findings...
Good luck.
AA


mark chandler - 29/1/19 at 06:51 PM

My plan is quite simple now

Have another go at hardening the stud, nut oil and shake it about, really should have read up a bit more on quenching oils, then temper.

Add a HSS nut, and try and break it by driving the stud through the nut on my press, if it can hold 10 tons I am in the safe zone.

Repeat with my expensive ARP nut, these may not be as deep as the HSS full nut which may be a problem.

If all goes well I am sorted, I am not expecting the stud to be an issue, the stretch bolts shank diameter is 8.1mm, my stud through the thread around 10mm, the weakest part.

If these fail as noted above its all about thread engagement, I will get some EN24 hex and machine up longer nuts and see how they work.

As I am cutting the threads, it's a wonderful thing watching your 60 yeast old lathe carve out perfect threads, far superior to using as dia, I can keep the clearances really tight, machine the thread diameter to the nut.

Threads in the block are fine, a long engagement, again I can keep tight.

It's a pity that pictures are hard to post, I am using an iPad so will copy to my laptop and transfer across, sticking elsewhere ends up with dead URL's after a while.

[Edited on 29/1/19 by mark chandler]


Dingz - 29/1/19 at 10:03 PM

I’d be more concerned now about pulling the stud out of the aluminium block however much depth of engagement you have. Any idea of the block material strength?


snapper - 30/1/19 at 05:39 AM

If you haven’t already done so read the extensive metallurgy info on the ARP website
Amongst other gems of info they harden the chosen metal before pressing in the thread.


Mr Whippy - 30/1/19 at 07:32 AM

Personally for all the cost of getting custom studs made that are certified and tested there is no way I'd be trying to make my own for something that could potentially cost vastly more when it fails, especially since you have boosted the engine as well so failure is even more likely. Really it sounds (don't take this personally) you don't really have the experience or the equipment to make these.

But then again it is your engine so go for it


James - 30/1/19 at 03:20 PM

Fascinating post Mark- thank you!

I'm amazed these can't be bought- what do 'normal' people do?

(Buy a new car I guess! )


02GF74 - 30/1/19 at 06:22 PM

If the studs you are after are made by ARP, who we'll pretty much agree know what they are doing, you need to weigh up the money saved vs cost to fix engine should it blow.

Thrown into the mix is how confident you are that the DIY studs won't fail.

As an alternative, have you looked at drilling the head and retapping the block to use a larger diameter stud?


mark chandler - 30/1/19 at 08:24 PM

It's a jaguar straight 6, AJ16 engine, these were originally designed to be diesel lumps, worst that will happen is the head gasket fails which has already happened, 1 day to replace once I get going, head gasket is £18 and maybe a skim required.

EN24 is plenty strong enough in this application, been used for years this is not a 2000hp drag car after all and I will make samples and destruction test before I fitting, if they fail I will bite the bullet..

My lathe is a quality industrial machine, 60 years old with very little wear as it came off a submarine of all things, tooling used is 60 degree thread insert so provided I get the heat treatment right it should be fine.

[Edited on 31/1/19 by mark chandler]


redturner - 31/1/19 at 01:22 PM

I don't know whether it is still available but we used whale oil as an alternative to water depending what we were hardening.....


mark chandler - 31/1/19 at 02:55 PM

quote:
Originally posted by redturner
I don't know whether it is still available but we used whale oil as an alternative to water depending what we were hardening.....


Thank you, I will try a litre of nut oil this weekend, this looks like a good option as capable of high temperature with good heat transfer properties and see where this takes me


coozer - 31/1/19 at 09:03 PM

Sure ARP dont make the studs??


mark chandler - 31/1/19 at 09:12 PM

I,m sure I can get rolled threaded studs made, it defeats having tooling to make something.

Second attempt, failed at 7 tons with a water quench, fit was slightly loose after treatment, dug out a HSS bolt and this failed at 4 tons in my press.

It's getting close to being usable now.

[Edited on 1/2/19 by mark chandler]


mark chandler - 2/2/19 at 06:35 PM

A bit more experimentation today, heat to 840 degrees for an hour, water quench and temper @ 340 degrees for an hours soak, now my stud strips the threads out of a hardened nut cleanly @ 7 tons with no deformation on my machined threads so now awaiting a set of ARP nuts to arrive so I can see where the fail point is with these.

The threads were a good fit before hardening, after the nut felt a like they had a little play so tomorrow I will try cutting the threads in hardened metal in an attempt to retain closer tolerances.

The thread depth by my DRO was 0.77mm, from the various tables I should be 0.77978 I assume as I am using the same bit of round for my experiments it may have reduced slightly with the constant heat cycles.


daviep - 2/2/19 at 07:36 PM

Excellent thread and I completely agree with your ethos on trying to do it yourself.

One question, what are the HSS nuts and bolts are you referring to? Presumably they are not High Speed Steel!

Cheers
Davie


mark chandler - 2/2/19 at 08:35 PM

This is the description

"high tensile, UNF full, hex nuts" they seem pretty good quality, 1/10th the price of ARP, I have 20 of these on route delayed due to snow so will be able to see how far above 7 tons I get.

When you look at the thread engagement it's amazing that they can sustain 7 tons of hydraulic pressure pushing the stud through the nut!


daviep - 2/2/19 at 11:35 PM

It maybe that you are using normal grade 5 nuts which are the imperial equivalents of metric class 8

It would be interesting to compare the results with a known grade 8 nut (equivalent of metric class 10).

7/16" Grade 5 nut should be good for at least 6400kgs
7/16" Grade 8 nut should be good for at least 8100kgs

Cheers
Davie


mark chandler - 3/2/19 at 12:09 AM

As someone noted earlier on, also the depth of engagement, bang at 7 imperial tons makes them grade 5 I guess, I was able to spin the thread off the stud as a spiral.

The ARP nuts should be tough, not sure how PSI compares to ton as it's rated sq/inch

Brand:ARP
Manufacturer's Part Number:301-8354
Part Type:Nuts
Product Line:ARP 12-Point Nuts
Summit Racing Part Number:ARP-301-8354

UPC:672036040864
Thread Size: 7/16-20 in.
Nut Style: 12-point
Nylon Insert: No
Self-Locking: No
Wrench Diameter: 5/8 in.
Nut Material: Steel
Nut Finish: Black oxide
Washers Included: No
Fastener Yield Strength (psi): 180,000 psi
Quantity:


daviep - 3/2/19 at 08:51 AM

For comparison

Grade 5 - 120,000psi
Grade 8 - 150,000psi
ARP. - 180,000psi

7/16" unf has a stress area of 0.1187 sq in

so for ARP nuts

180,000 * 0.1187 = 21,366lbs or 9712kgs

Regards
Davie


Oddified - 3/2/19 at 09:04 AM

quote:
Originally posted by daviep
For comparison

Grade 5 - 120,000psi
Grade 8 - 150,000psi
ARP. - 180,000psi

7/16" unf has a stress area of 0.1187 sq in

so for ARP nuts

180,000 * 0.1187 = 21,366lbs or 9712kgs

Regards
Davie


Nearly 10 tons..i think you'd have to be running some serious boost to need that per stud.

Ian


mark chandler - 3/2/19 at 12:17 PM

It also has 14 of these pulling down the head, 12psi today, I am hoping this will drop when the ported head goes on as the Eaton is just stirring air, pressure is just what's being backed up in front of the valves.


Oddified - 3/2/19 at 01:40 PM

From what i've seen/experienced most Eatons are best kept below 10psi, exponential diminishing returns above that with heat and power loss.

Ian


mark chandler - 3/2/19 at 06:22 PM

The inlet heat is pretty much out of control, I have a decent sized intercooler which I had recored a few months ago, it's better but after a 15 seconds at WOT the inlet temperature jumps 40 degrees - much better than before... It recovers quickly although I need a new front charge cooler radiator.

I,m hoping with a much better flowing head to see a drop in inlet temperatures as its will not be having to work so hard, I have ported it as far as I dare go which made a decent improvement.

With the size of pulleys it's running at its limits, I did think about modifying a m112 to fit however research shows that these are very inefficient at moving air fast, okay better at lower RPMs

[Edited on 3/2/19 by mark chandler]


mark chandler - 23/2/19 at 04:53 PM

Slow progress on this as I have been awaiting ARP nuts to test my thread strength, 12 arrived on Thursday with more on there way - ARP nuts are lovely compared to the other ones I have.

Today I heated 2 short lengths of EN24t to 840 degrees C and let it soak for an hour then quenched in the correct oil, both came out nice and hard.

Next I machined one in the hardened state with a really good fit, the other out to one side then tempered both at 400 degrees C, which gives W grade hardness - researching TWR had their own studs for racing XJS's, they used W hardness 9/16 studs.

I now threaded the heated and tempered sample and moved to destruction testing, it did not pan out that way as both can withstand over 10 tons of pressure, I will make 14 studs tomorrow , threading then annealing to stress relieve.

Head is not due for a couple of weeks so I will clean the injectors and flow test using an old pump and regulator to see if they are good for another year.

I asked ARP to quote for rolled threaded studs, they showed zero interest in making anything, either contacting directly or via an agent so Hobson's choice, "We make some for XK engineering, call them" unsurprisingly XK engineering do Jaguar XK engines not AJ16 so a complete waste of time.

[Edited on 24/2/19 by mark chandler]


britishtrident - 23/2/19 at 08:29 PM

Everybody misunderstands stretch bolts, once a stretch bolt had been used once the elastic limit of the bolt actually increases, use it again and increases further the bolt isn't weakened. The value of E of the steel and the ultimate tensile strength is not altered. Undo and re-use too many times and the strain (nb not stress) failure limit is eventually reached and the bolt will start to neck and weaken.

Stretching beyond the elastic limit is how piano wire is manufactured so it retains its tension in use and to make it its properties more predictable.


mark chandler - 23/2/19 at 08:46 PM

That may be so, Aston Martin rate the ones I have pulled out the engine as good for 10 uses provided they meet measurement specifications.

Problem is the use of UNC threads in the block, correct for studs so a hang over from the past but too aggressive for stretch bolts as you are exerting so much force twisting them they are not really pulling the head down - hence my move to studs as I am getting 30% more power out the engine 3.2 putting out +400hp


phelpsa - 24/2/19 at 08:39 AM

T&K Precision will do you a set in S99G (12.9 equivalent) for £12ish a stud. S99G has been pretty much the motorsport industry standard for studs and fasteners for some time is it's easy stuff to get hold of if you want to make them yourself.


mark chandler - 24/2/19 at 05:54 PM

Thanks, I will bear that in mind, for now my single point cut EN24W studs will be going in my car the money has been spent, all £34 👍


phelpsa - 24/2/19 at 06:44 PM

quote:
Originally posted by mark chandler
Thanks, I will bear that in mind, for now my single point cut EN24W studs will be going in my car the money has been spent, all £34 👍


Good stuff