exhaust manifold stud material

[Lambolica]

Factory Studs would be 8.8 Grade, you can go up 10.9 or 12.9, but there is no way living that an exhaust manifold stud is going to fail even at 8.8.

OC: correct me if I'm wrong but the higher grades would be more prone to shear failure? less ductile and more brittle?

Cheers
Simon

[oldcorollas]

at higher temp, all grades will reduce strength.. if you start with a weak bolt, then it might stretch once it gets hot (depends how hot we are talking tho)
they might be more prone to fatigue failure, but not many bolts have high enough forces on them to shear (sideways)

if you look at this (very general) guide, you will see that only the shittest of shit bolts are mild steel (low carbon steel).. ie grade 2.
http://www.boltdepot.com/fastener-in...ade-Chart.aspx
then again, here it has up to grade 5 as low carbon http://www.engineersedge.com/hex_bol...tification.htm

i would suspect that something like 8.8 (or any high tensile bolt) will be so underloaded, that they would not fail, even with fatigue loading.
more of an issue is corrosion and nut sticking.. steel and steel will rust, but staino will also stick together.
at least on old rollas, they still used brass nuts but i'm sure they are not strong enough for turbo application..

i don' thave anything calibrated enough to check the carbon content accurately, but i could do hardness tests or check microstructure


ductile vs brittle... if you have ever overtorqued a head bolt to failure, that is sudden brittle fracture. (with a bang)
whereas if you get some galvanised or bright bolts from the bunnings shelf, and overtorque them, they will twist and stretch and slowly fail (like licquorice)... you really need to load up or abuse a high strength bolt to get it to fail...

[Lambolica]

Or get a poorly made bolt.

Most failures on exhaust stud would be from actually trying to remove a nut off a seized stud (or Torsion failure / Shear failure). I'm yet to hear of a tension failure.

So my question would be: what does the cycling of heat do to the higher tensile strength bolts in that they fail after many years in torsion? surely the temps in an N/A manifold/head don't get to the point of altering the crystalline structure of an 8.8 bolt?

Cheers
Simon

[Draven]

but i'm sure they are not strong enough for turbo application..

Quoted for truth.

I munted a variety of brass bolts before going cone locks on high tensile studs. no issues since
(on dump pipe I'm talking, but similar temps to manifold)

[broken22]

Thanks for the input so far guys.
I might price up some OEM studs/nuts.
Has anyone used titanium nuts on steels studs, theory is they expand at different rates so dont come loose.

[love ke70]

wouldnt expanding and contracting at different rates cause looseness?
when i got my manifold from kyle at 6boost, it came with studs, they were those goldy coloured suckers, i never had an issue with those, and that car saw alot of heat running on LPG and plenty of boost in a very small bay.
came off nice and easy when i needed them too

[oldcorollas]

goldy would be the chromate conversion layer applied to stop corrosion.. did it burn off after use?

[love ke70]

think it might of on the tensioned section of thread, but the nuts and exposed thread dulled but were still goldy.
is that an indication of how hot, or not hot it was getting, or just a question?

[oldcorollas]

not sure, but i can stick some in a furnace there must be some temp at which the coating changes, since it is only for usual temps..
maybe the bolts aren't getting that hot?

[Z2TT]

When removing the nuts, would heating either the nut or bolt (not both) with a blowtorch, make the Nut come off easier?

[AAAAGZE]

for those who want ridiculously high tensile exhaust studs,

Socket set screws, or Grub screws are 14.9 grade, and they have an allen key drive, so they're easy to install and remove later.



-dave

[LeeRoy]

I munted a variety of brass bolts before going cone locks on high tensile studs. no issues since
(on dump pipe I'm talking, but similar temps to manifold)

As I said above cone locks held my turbo on and getting it off I sheared/stripped bare every single stud. Have fun if you ever want to remove it

Although to be fair theyre often the only nuts that will stay on.

When removing the nuts, would heating either the nut or bolt (not both) with a blowtorch, make the Nut come off easier?

You'd only want to heat the nut so it expands and loosens it off the stud - although in reality you would more than likely heat both so something like innox would be better.

If theyre super tight even an angle grinder and throw the nuts in the bin - nuts are cheaper than studs, and even cheaper than buying an easy out kit to remove a broken stud from a head. Not to mention the time taken to do this.