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Author: Subject: Hardening steel
mark chandler

posted on 28/1/19 at 10:06 PM Reply With Quote
Hardening steel

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]

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melly-g

posted on 28/1/19 at 10:19 PM Reply With Quote
I'm by no way an expert on this but you wouldn't want to use synthetic oil for this would you?
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mark chandler

posted on 28/1/19 at 10:45 PM Reply With Quote
I just used what was lying around, may have been a mistake this is a test pieces so not an issue at this stage.
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loggyboy

posted on 29/1/19 at 12:13 AM Reply With Quote
Why not use water?
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gremlin1234

posted on 29/1/19 at 12:17 AM Reply With Quote
why harden the studs, when they will shortly be subjected to a lot of heat/ cool cycles, which will probably soften them again?
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Angel Acevedo

posted on 29/1/19 at 12:19 AM Reply With Quote
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





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mark chandler

posted on 29/1/19 at 07:18 AM Reply With Quote
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]

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CNHSS1

posted on 29/1/19 at 07:20 AM Reply With Quote
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





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Mr Whippy

posted on 29/1/19 at 07:23 AM Reply With Quote
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?

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JAG

posted on 29/1/19 at 09:32 AM Reply With Quote
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]





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rusty nuts

posted on 29/1/19 at 11:31 AM Reply With Quote
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?
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mark chandler

posted on 29/1/19 at 01:17 PM Reply With Quote
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

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JAG

posted on 29/1/19 at 02:04 PM Reply With Quote
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]





Justin


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Angel Acevedo

posted on 29/1/19 at 03:59 PM Reply With Quote
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





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mark chandler

posted on 29/1/19 at 06:51 PM Reply With Quote
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]

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Dingz

posted on 29/1/19 at 10:03 PM Reply With Quote
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?





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snapper

posted on 30/1/19 at 05:39 AM Reply With Quote
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.





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Mr Whippy

posted on 30/1/19 at 07:32 AM Reply With Quote
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

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James

posted on 30/1/19 at 03:20 PM Reply With Quote
Fascinating post Mark- thank you!

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

(Buy a new car I guess! )





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02GF74

posted on 30/1/19 at 06:22 PM Reply With Quote
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?





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mark chandler

posted on 30/1/19 at 08:24 PM Reply With Quote
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]

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redturner
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posted on 31/1/19 at 01:22 PM Reply With Quote
I don't know whether it is still available but we used whale oil as an alternative to water depending what we were hardening.....
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mark chandler

posted on 31/1/19 at 02:55 PM Reply With Quote
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

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coozer

posted on 31/1/19 at 09:03 PM Reply With Quote
Sure ARP dont make the studs??





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mark chandler

posted on 31/1/19 at 09:12 PM Reply With Quote
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]

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