Exhaust manifold studs

[track_addict]

Preparing my motor to go back in and I need to replace 3 of the manifold studs. Got a price from Mazda, they want drug money ($10 a stud). I spoke with the engine builders and they're struggling to find some aftermarket studs since it seems that not many people do header studs and if they do they're all UNC/UNF. Are the Mazda studs good enough for a turbo street/track car? I'm guessing probably not since 3 have fallen out already. What are the aftermarket options, if any?

[NitroDann]

Which studs specifically?

[track_addict]

Head to manifold. Sorry, should of specified in the OP.

[pezchops]

is there any reason you cant buy high tensile threaded bar and cut studs to length?
buy high tensile bolts with long enough threads and cut off to length?
any Bolts and Industrial outlet will help you out.
probably save a little bit.
so long as the studs are the correct tensile strength and you use the correct thread locker it should be good.
i dont have direct experience with manifold studs but in general engineering, so i might be missing something?

[NitroDann]

OK,

Chase the threads, use new studs from the muffler shop/ebay, locktite if you hate your future self, and torque them in and it will be good.

Dann

[chrons_rotary]

is there any reason you cant buy high tensile threaded bar and cut studs to length?
buy high tensile bolts with long enough threads and cut off to length?
any Bolts and Industrial outlet will help you out.
probably save a little bit.
so long as the studs are the correct tensile strength and you use the correct thread locker it should be good.
i dont have direct experience with manifold studs but in general engineering, so i might be missing something?

It isn't about having a high tensile strength, it is more about being able to withstand the extreme temps, and the heating/cooling that happens to those studs.
While genuine Mazda studs will be best, like Dann said, you can just go to a local mufflers shop and get some studs from there.
Also while you are there, might as well get some new nuts too, since they will be just as old.

[hks_kansei]

Look for wherever your nearest bolt/fasteners shop is.

They should have them, if not can order them, and are usually cheaper than the other options.

[track_addict]

Great, thanks guys. Going to the fastener shop this arvo for some other stuff, so will ask then. Will not be loctiting them in. Engine shop warned me of that. They also said NOT to use lock nuts. They say, when you go to remove them after a while, they don't release the thread and you end up either winding the stud out or, worse, snapping it. Can anyone shed some light on this? Are plain nuts, torqued up, acceptable?

[Mr Morlock]

$10 each- chicken feed for the right product. Often with the local bolt shop you don't really know what you are getting insofar as bolt specs are. Threaded rod is normally just M/s its not hardened rod and if you ask them what is the spec expect a don't know answer. Most of the stuff you see is just soft rod with clear zinc plating which would be useless in a stress environment. You can mess about trying to save a few dollars and spend more time than "your" time is worth.

[hks_kansei]

Most OEM applications just use flared nuts, so thats what i'd use.

Pretty sure at my GF's work she uses regular nuts and a spring washer on their builds, but that's also on non-crossflow heads, so the one nut is holding tension on both the exhaust and intake manifolds together.



Don't use Nylocs, the heat will just melt the nyloc bit out anyway.

[hks_kansei]

$10 each- chicken feed for the right product. Often with the local bolt shop you don't really know what you are getting insofar as bolt specs are.

Most fastener shops are very knowledgable in the product, the specs, and the recommended usage of the item.
After all, they specialise in it.

the $10 stud from the engine builder's workshop is most like the same one as at the bolt shop (since the bolt shops main trade is to shops like engine builders etc)

[NitroDann]

Having built and dealt with these issues on 70 odd turbo MX5's I feel that this answer is pretty accurate.

For head-> manifold, have clean threads, all of them, not just the ones that came loose. Replace all of the studs with new ones, nothing fancy is required, but they do need to be exhaust studs with the unthreaded centre section. Tension the studs down hard on the unthreaded section, you may use low strength loctite, it releases with heat, so there is no reason to not use it if the person who next removes them is made aware.

Use OEM style nuts, these are flanged, serrated nuts.

Tighten all nuts gently and then Torque to spec from the middle nut outward, like smoothing a crumpled sheet of paper. This keeps the flange dead flat and sealing well.

Never think about it ever again.

Dann

[track_addict]

Thanks Dann. Have ordered a new set of OEM studs and nuts.

Morlock. Sounds like your getting your local bolt shop and the bloke who works at your local supercrap/repco, mixed up. Or your local bolt shop doesn't know much. I know how much my time is worth, and to be honest, its worth more than the time I spent typing this reply to your uninformative post.

[track_addict]

So, I went and got a new set of studs and nuts from Mazda, will put them in on the weekend. Just want to ask what the best practice is to go about it. Just get two plain nuts and wind them on the studs still in the head, then wind them out? Or will I need some heat/inox/wd40 to help the stud come out cleanly? Also, what sort of torque should I be applying to the new studs? Just standard torque for a M10 thread? Or elbow torque with a ratchet (less preferred on my part)?

[NitroDann]

Soak them in penetrating fluid (wd40).

Double nut, start by working them in and out a bunch of times to break down any corrosion between the threads, then wind them out.

Torque the new studs in hard.

Dann