What tensile strength are cylinder head studs?

[Davezj]

I will be needing to replace my head gasket soon I am looking in to replacing the standard head bolts with high tensile studs.
so how strong do the studs need to be.
8.8 threaded bar is available all over the place, is that strong enough. I don't want it to stretch. As I am in two minds weather the current head bolts have stretched or not. I haven't started the full diagnostic procedure yet. So this is just a pre emotive question about replacing head bolts with head studs to allow me to run more boost.

Any thought would be good.

The reason I mention the threaded bar is head studs are stupidly expensive for a set.

I know you can get ARP 203-4204 head studs for an mr2 engine but you need two sets of them for the 6a13tt engine @peter Thompson used these for his engine.
You can also get a set for 6a13 from rpw which has the correct quantity of studs, but that is $450 NZ.

[adaxo]

AFAIK head bolts are designed to stretch under hot/cold condition together with head/engine block (expand and shrink metals) and its not good idea to just change them to 'stronger' ones, they could cause head to split. It will be probably OK to change for 'tuned' and designed ones from ARP or similar tuning companies.

[Nick Mann]

Also remember that higher tensile strength, due to requiring less deformation, often goes hand in hand with making the bolt/stud more brittle. Having said that I would imagine that the stock bolts are a lot stronger than 8.8 anyway.

[Davezj]

I am sure I get stronger stud bar than that but it was more of an example.
I will be changing to studs only if I find the head bolt that are in my engine at the moment are overly stretched.
So it all depends on what I find.
Just trying to find the info.

[adaxo]

One more thing to consider is, if you use studs, are you be able to fit heads (especially rear one) with engine in situ??or engine need to be removed from car to get enough room for fitting head?? I'm not saying 'not', just a thought.




off topic slightlyave, just not end up like this guy

[Davezj]

Yes that is a very valid point, and one I must consider.
If I fit the manifolds after the heads are fitted, to the block then fit he turbos it will probably be ok, but will have to check.

[adaxo]

Fitting exhaust manifold with turbo on fitted head is huge PITA and close to impossible to do it properly (all bolts torque to correct Nm) I will not advise to do this way as I just made this little mistake not long ago.

[Davezj]

I was thinking heads on then manifolds then turbos then turbo elbows.
But that is some way off.

[Davezj]

Here is some
10.9 tensile strength.
http://www.shop4fasteners.co.uk/acat...elf_Colour.asp

Here is some info on stretch head bolts, how good it is I don't know, but seem logical.
http://www.gomog.com/allmorgan/stretchbolts.html

Here is some info on the difference between the markings on bolt tops
http://www.tessco.com/yts/customerse...bolt_grade.pdf

Here is another comparison chart
http://www.americanfastener.com/tech...ings_steel.asp

What have noticed is the commercially available threaded bar only seems to go up to 150,000psi
And head studs are being quoted at about 200,000psi standard and up to 265,000psi for some cosworth parts.

Maybe I need to re think the option unless I can find a supplier of some stronger stuff.

Now have a look at this, it is not a surprise ARP one of the top fastener companies in world with a material range and strength range like this
http://arp-bolts.com/pages/technical_metallurgy.shtml
From about point 18 onwards.

[Gowf]

For what purpose do you need uprated bolts/studs? If you are changing gasket material then ok, but even then you will have a different torque setting.... If its because you are scared of blowing gaskets, there must be a reason for that, so better to identify it rather than just trying to weld the heads down? After all you want to treat the gasket like a fuse and get it to blow first, otherwise you'l find that your pistons take the brunt (if we are talking about excessive heating causing it) Below 2 bar I wouldnt say that you need them.

[Davezj]

Cheers for you comments Garth, this is a very brief history of what has been going on with my car.

At present I started hitting issues with 1.4-1.5 bar combustion gas in cooling system after japfest II on track session1, when I thrashed the life out ofthe car.
Then went out for track session 2.
With hindsight that was probably not the best thing to do.
But now with he boost turned back down to stock pressure I don't have any major issues. If I do a sniff test on the coolant gases I only get a slight change from dark blue to a slightly light blue of the fluid.

Knock and AFR are ok at 1.4-1.5 bar. I just think I pusher it too hard for too long on track. The coolant was properly boiling, steam from the rad cap with a whistle.
But since japfest it has driven really well on lower boost, still very responsive.

[taylor]

IIRC the 6a headstuds are 10mm vs 4g63 being 11mm. The evo ones are 2mm longer, Id suggest re-tapping the block to accept the 11mm evo studs and using ARP ones.

Use proper head studs/Bolts, not DIY threaded rod. Bad Idea.

[Adam.Findlay]

IIRC the 6a headstuds are 10mm vs 4g63 being 11mm. The evo ones are 2mm longer, Id suggest re-tapping the block to accept the 11mm evo studs and using ARP ones.

Use proper head studs/Bolts, not DIY threaded rod. Bad Idea.

+1
high tensile steel is treated in a specific way, (both heat treated and tempered) to give the best possible strength and fatigue properties,
ARP know what they are doing where as some bloke who sells you some "high tensile" rod and nuts probably doesnt have a clue
Im in the process of finding a source for ARP studs through a friend. will report back here when I get an answer.
as taylor said drilling and tapping the block to accept the bigger bolts could be an option but oil feeds and galleries need to be watched out for when drilling holes in the head and block bigger.

[taylor]

+1
high tensile steel is treated in a specific way, (both heat treated and tempered) to give the best possible strength and fatigue properties,
ARP know what they are doing where as some bloke who sells you some "high tensile" rod and nuts probably doesnt have a clue
Im in the process of finding a source for ARP studs through a friend. will report back here when I get an answer.
as taylor said drilling and tapping the block to accept the bigger bolts could be an option but oil feeds and galleries need to be watched out for when drilling holes in the head and block bigger.

You should be ok @ 1mm difference, as the 4g63 (very similar head design) often are stepped up to 12mm studs.

a quick look in ASA shows a CM5A GSR uses the same Bolts.. Whether or not thats any help..

[taylor]

Also the way the threads are made are substantially different on ARP fasteners compared to bog standard threaded rod..

I believe ARP cold roll their threads.

[Adam.Findlay]

threadded rod is usually machined thread which causes yuck machining marks in the material making it weaker. yes ARP's are rolled threads which results in a smoother therfore stronger thread.
and yes 4G93T head studs are the same.
some 3sgte ones are the same also from memory. will try get a price up for a complete set for 6a's

[wintertidenz]

You can get the head bolt sets for significantly less at STA Parts here in NZ. $40 NZ for a set of 16.

www.staparts.co.nz - part # HBS040AJU

[Adam.Findlay]

that would be std torque to yeild type bolts. the good thing about the ARP jobbies (despite the cost) is they are not torque to yeild so can be reused

[Davezj]

You can get the head bolt sets for significantly less at STA Parts here in NZ. $40 NZ for a set of 16.

www.staparts.co.nz - part # HBS040AJU

that is a very good price for a standard set of head bolts for the 6A13tt engine, albeit an after market supplier.
if i find i don't need to use high stensile studs then i will probably get some of these, but as i said above it all depends on what i find under the rocker cover, if it is a lot of loose bolts then i might go down the stud route.