Exhaust Stud Removal

[Tom]

I'm not sure I see the jig in the first picture. If it doesn't bolt to the head to keep the drill hole perfectly centered over the hole, I would not trust it. (And if it doesn't bolt down, what it is supposed to do??)

[danmartinic]

That break appears to be more-or-less flush with the head. If you're going to drill it out, I highly recommend the jig. Otherwise the bit is going to do its damnedest to wander.

As for getting the rest of the nuts off, get an inductance heater. Nothing else comes close in terms of utility. You may need to heat-cycle them a couple of times (with some penetrant in between) to get them loose.

I do have a spring-loaded centre punch I believe small enough to use down there.. that would get me started right without wander, no?

I'm pretty sure the nuts wouldn't be a problem esp with a little heat from a small torch (in any case maybe my advantage if they are stuck so I don't need to double nut); it's the studs that I'm worried about. Induction heaters are $$$ and I'm still not sure why a warm engine & head wouldn't make that easy? I am reading something about galling the threads if too warm.. but doesn't using heat in any capacity incur the same risk?

[danmartinic]

I'm not sure I see the jig in the first picture. If it doesn't bolt to the head to keep the drill hole perfectly centered over the hole, I would not trust it. (And if it doesn't bolt down, what it is supposed to do??)

Jig with adapters behind it (and one installed).. meant more for wood projects I think but basically, if I get a small hole started (centre punched), I thought I could hold this thing flat against the head side and the drill bit guide keeps it 90 degrees

IMG_3202 1.jpeg (2.49 MiB) Viewed 169 times

That said... I DO have access to a 3D printer.. though not sure what filament options. I'm in no particular hurry. If you want to make a file, I'll wait

[jeyjey]

My experience with a spring-loaded centre punch is mixed at best. It's hard to get them perfectly centred especially when the break is not flat. And the punch usually has a much narrower included angle than a split-point drill bit, so you still get some wander.

My guess is the thread galling issue is a result of undoing the stud while it's still hot. Remember, you're just looking for the thermal changes to break down the rust, etc. I never put torque on the nut/stud/whatever until after it's cooled back down.

[danmartinic]

My experience with a spring-loaded centre punch is mixed at best. It's hard to get them perfectly centred especially when the break is not flat. And the punch usually has a much narrower included angle than a split-point drill bit, so you still get some wander.

Ahhhh... I see. Well then... it might be Tom to the rescue

[jeyjey]

That Stromski Racing jig is pretty sweet....

[Tom]

My experience with a spring-loaded centre punch is mixed at best. It's hard to get them perfectly centred especially when the break is not flat. And the punch usually has a much narrower included angle than a split-point drill bit, so you still get some wander.

My guess is the thread galling issue is a result of undoing the stud while it's still hot. Remember, you're just looking for the thermal changes to break down the rust, etc. I never put torque on the nut/stud/whatever until after it's cooled back down.

Agreed on the center punch, but I'd go a step further and say it's mighty hard to nail the exact center of a broken bolt with a punch -- and especially on the side of a head with limited access/visibility. Even if the bit doesn't wander (it will), if you are half a mm off center, the hole will be half a mm off... I'll make you a jig. Which stud is is? If the frontmost one is #1 and the one closest to the firewall is #8.... Knowing that will help make sure I pick up the best locating holes...

[dr bob]

I use an "indexing punch" that pilots in the drill bushing in the jig. I bought a set of them a brazillion years ago for just such episodes. It does demand a rather square end on the stud. With care and gentle initial taps it will start a dimple in the center. You do still need the fixture.

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The steel drill bushings are certainly readily available. I'd be tempted to print the holder for them, drop the steel drill bushings in, index punch the center of the stud, then the drill progression.

The video has a P drill for the last in the sequence. I'd need to look to confirm, but there's a good chance it's the same size drill you might use to pilot a hole you intend to tap for 8mm threads in new metal. You'll struggle to find a drill bushing with a P drill ID, so some adjustment may be needed to get it "just right". The drill will quickly walk to the softer aluminum head metal if the diameter or the center aren't almost perfectly concentric.

Does anybody else use copper anti-seize on the exhaust studs/nuts? That's what I used when I had 911's. Since then I've had the luxury of working with some serious techs in power plants. The gas turbine guys use a non-metallic "nuclear grade" anti-seize that's good to some pretty extreme temps. Think 1200ºF+ for combustor cans. Not as cheap as parts-store silver or even the copper stuff, but considering the downsides it's worth the cost at least for me. You do get to adjust torque settings for the not-dry threads, but again it's a small distraction considering the downside risk. You can buy it on Amazon.

When you do have to install new studs, give very careful though to whether you really need "stud and bearing mount" LocTite. Use a thread chaser (vs. a tap) to clean the thread. The LocTite goes only on the last few threads on the stud, the last ones that go into the head metal. Should you ever need to remove one, heat on the stud will soften the LocTite without having to red-hot the whole head and port.

There are also some handy small "induction heaters" that make very nice focused heat zones around the steel studs in the aluminum. Need to break an oxidation or galvanic bond with some quick focused heat, this is exactly your tool.


Back to our normal cocktail discussions...

[jeyjey]

P is 8.2mm(-ish); tap drill for M8 is 6.7mm (between G and H).

If you stopped at 1/4", I wonder if it would release enough of the tension that what remained would be easy to screw out? If not, you could probably go very carefully from 1/4" to G without a bushing.

I used Copaslip on my exhaust studs (and the copper-plated nuts).

[gpr8er]

FWIW I'll chime in. I haven't had the misfortune of dealing with a broken exhaust stud in the head and worse in car. But have had experience with having an EDM extraction. That being said years ago I pulled all the exhaust studs and replaced them with the same bolts as used in the intake manifold, the perfect size and length using copper anti seize. Makes life so much easier when R&R the exhaust manifolds not having to fight the manifolds around the studs. Everyone knows how those things warp.