Broken exhaust stud removal

[Astro14]

For a low torque/low stress application, like this, helicoil. There just isn’t that much stretch on the studs, helicoil will be great. Drill it square, cast iron will drill and tap easily, but the remnants of the studs will be hard to drill, which means that the bit can get off center, off square, easily. If you have a drill press, that would be best to preserve the drill path and keep it square.

 

[JHZR2]

For a low torque/low stress application, like this, helicoil. There just isn’t that much stretch on the studs, helicoil will be great. Drill it square, cast iron will drill and tap easily, but the remnants of the studs will be hard to drill, which means that the bit can get off center, off square, easily. If you have a drill press, that would be best to preserve the drill path and keep it square.

Thanks. My greater concern is that the flange isn’t parallel to the manifold side, so I need to get it shimmed and leveled just right. Not the end of the world by any means. But just need to get that right, and then ensure that when I plunge in to drill out the hole, and the whole thing torques to the side, that it doesn’t all shift.

I can see that trying to get it starting to cut with that hardened stainless in there might cause a bit to snag.

 

[CleanSump]

Thanks. My greater concern is that the flange isn’t parallel to the manifold side, so I need to get it shimmed and leveled just right. Not the end of the world by any means. But just need to get that right, and then ensure that when I plunge in to drill out the hole, and the whole thing torques to the side, that it doesn’t all shift.

I can see that trying to get it starting to cut with that hardened stainless in there might cause a bit to snag.

Slow and steady, tiny short turns, remove and clean often, use lots of real tapping or cutting oil with sulfur in it.

 

[JHZR2]

Ok, I’m not exactly sure how I’ll do it, because the angles of the manifold don’t work well for securing it to my drill press. But something like this:

A minor point of concern. I think heating the studs may have caused some minor cracking of the manifold flange. I tried to heat very evenly all over, not just one spot. But the end shows a crack that isn’t quite through, but is visible and was not in my earlier photos:

Should I be concerned?

 

[JHZR2]

Helicoil.

Thinking out loud, given the cracking, would the strength of a time sert which has a wall thickness and adds more structure be better than a helicoil?

 

[Pablo]

Drill and tap. Any further material removal will just make it weaker.

You've come this far kind of thing and probably most in the junkyard will look the same

 

[CleanSump]

What @Pablo said. Use as big a washer as possible to spread the load on the flange when you put it back together.
Edit: A thick washer and heat treated. You can grind one side down to clear the casting if you have to.

 

[JHZR2]

Drill and tap. Any further material removal will just make it weaker.

You've come this far kind of thing and probably most in the junkyard will look the same

Thing is, I know that unfortunately this cracking was due to the heating. As it wasn’t that way before.

Do you think helicoil at least is going to remove that much more material to weaken it much? It would seem to me that better quality threads would be desirable as compared to some hybrid stainless-cast mix that I tap.

Of course I guess tapping could ideally just remove the stainless from the grooves. But I doubt it.

 

[Astro14]

Helicoil removes less material than Timesert.

I would lean towards helicoil

 

[D60]

Ok, I’m not exactly sure how I’ll do it, because the angles of the manifold don’t work well for securing it to my drill press. But something like this:

View attachment 336836

A minor point of concern. I think heating the studs may have caused some minor cracking of the manifold flange. I tried to heat very evenly all over, not just one spot. But the end shows a crack that isn’t quite through, but is visible and was not in my earlier photos:

View attachment 336837View attachment 336838View attachment 336839View attachment 336840View attachment 336841View attachment 336842

Should I be concerned?

I'd build a jig with the exact 4-bolt pattern. It could bridge over the manifold as shown to "hang" the work plumb and square, but truthfully with a jig and some drill bit bushings you could probably do this on the bench with a hand drill.

A Timesert theoretically "wedges" and could maybe "blow out" the walls. In truth, doubt it matters

 

[JHZR2]

Helicoil removes less material than Timesert.

I would lean towards helicoil

Helicoil wants 21/64, which is 0.328” or 8.33mm to tap. Their tap is supposedly m10x1.25 size (a nut of that size will ride the tap down), but it’s STI thread(?). M10x1.25 is 0.394”.

Time sert wants a drill that is “0.323” (per their chart, has a letter designation). Their tap is 0.381.

I’ve also read that both use STI taps. Of course they could be different sizes.

Seems like splitting hairs while time sert provides less chance of errors and more structural material to thread into.

Not being argumentative just trying to do full due dilligence.

Drill and tap. Any further material removal will just make it weaker.

You've come this far kind of thing and probably most in the junkyard will look the same

I do think I’ll try this on my way towards the helicoil. Reason being that I’ll need to drill out larger than the M8 tap regardless if I’m to helicoil it (see dimensions above). Thus it can’t hurt to try, and may result in a fine outcome. Not a fan of some new hybrid stainless/cast cut thread, but it seems the worst that could happen is to drill out with the 21/64 for the helicoil anyway.



Process question, should I chamfer first? Kits obviously don’t come with that, and I’ve not seen that step stated, but it would seem to me to make sense to help center my drilling. Saw that step done by a slightly more professional video here:

 

[Trav]

One difference is the Time Sert swages in the iron possibly further weakening the already weakened part, while the Heli Coil just threads in with no additional stress. The Heli Coil is stronger than the Time Sert in a stud application, there is no rotational force on the threads only axial tension which is where the Heli coil shines. Time Serts have advantages in a few applications but the high price and all the hype does not make it any better than the cheap coil.

 

[D60]

I think Timeserts make sense for repeated use like drain plugs. For a manifold that you're not taking apart every 5000 miles, a coil is just as good.

That's probably noted in the vid -- I didn't watch it but think I saw it long ago if it's the one where JB does surprisingly well.

 

[D60]

Helicoil wants 21/64, which is 0.328” or 8.33mm to tap. Their tap is supposedly m10x1.25 size (a nut of that size will ride the tap down), but it’s STI thread(?). M10x1.25 is 0.394”.

Time sert wants a drill that is “0.323” (per their chart, has a letter designation). Their tap is 0.381.

I’ve also read that both use STI taps. Of course they could be different sizes.

Seems like splitting hairs while time sert provides less chance of errors and more structural material to thread into.

Not being argumentative just trying to do full due dilligence.



I do think I’ll try this on my way towards the helicoil. Reason being that I’ll need to drill out larger than the M8 tap regardless if I’m to helicoil it (see dimensions above). Thus it can’t hurt to try, and may result in a fine outcome. Not a fan of some new hybrid stainless/cast cut thread, but it seems the worst that could happen is to drill out with the 21/64 for the helicoil anyway.



Process question, should I chamfer first? Kits obviously don’t come with that, and I’ve not seen that step stated, but it would seem to me to make sense to help center my drilling. Saw that step done by a slightly more professional video here:

Countersinks are more for "guiding" a threaded fastener into place. It's mostly about ease of assembly, and knocking down problematic burs.

But yeah, any machinist will pretty much c-sink ANY hole they create. It's like trim around a door frame: a finishing touch that reflects a professional job

If you don't own a few c-sinks.....well, I'm disappointed in you. 90* is good for general use. I've got sets of 60, 82, 90 and 110 but that's overkill for most.

Many step bits will also countersink provided your hole is close in size to one of the steps.

 

[JHZR2]

Countersinks are more for "guiding" a threaded fastener into place. It's mostly about ease of assembly, and knocking down problematic burs.

But yeah, any machinist will pretty much c-sink ANY hole they create. It's like trim around a door frame: a finishing touch that reflects a professional job

If you don't own a few c-sinks.....well, I'm disappointed in you. 90* is good for general use. I've got sets of 60, 82, 90 and 110 but that's overkill for most.

Many step bits will also countersink provided your hole is close in size to one of the steps.

I have some, I guess the size and angle doesn’t much matter here, so long as it’s big enough?

 

[D60]

I have some, I guess the size and angle doesn’t much matter here, so long as it’s big enough?

Yep that's exactly right. Only really matters for FHCS (flat head cap screws) or wood screws

 

[spasm3]

The big question is, as difficult as it was to drill the hardened stainless, will a tap be able to cut threads in that same hear hardened stainless?

 

[JHZR2]

The big question is, as difficult as it was to drill the hardened stainless, will a tap be able to cut threads in that same hear hardened stainless?

Exactly right. That is the risk/issue/concern.

Thing is, drilling at 6.8mm then tapping to m8 doesn’t impede my ability to drill and helicoil, as that helicoil drill is larger than the major dimension of the m8. If I try to tap and it fails it’s just a step in the path to drilling out for the helicoil. So it doesn’t seem like I have much to lose, and I’d guess I have much to gain in terms of less work and risk…