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How to drill out exhaust bolts?

So when I was removing the exhaust from my 986 from the cat back, the nuts were too rusty to be removed the conventional way. They easily snapped right off. 5 out of 6 snapped without really a lot of effort. I thought, no biggie, I will drill them out

Well, I was able to drill 1 out with moderate difficulty, however moving on to the next, I have only been able to get it about 3/4th way drilled out.

I have burned through or broke probably 15 drill bits in this effort so far.

The best method I was able to figure out was to grind off the ends and then start by drilling a small hole through the bolt and moving up to a larger one with about 5 different sizes to get to 8.3mm. The actual hole is about 8.5mm roughly. The stud that is there was pressed in with splines. there is no way it is coming out by hammering it out. Using oil on the bit and the drill at a lower speed was the only way to get some cutting to happen.

So I have pretty much conceded defeat on the standard drill bit method. With at least 3 or 4 more holes to drill I need to find a better drill bit.

Is there a better tool for this?

Edit: I think I need to find some tungsten carbide bits.

Last edited by steveng1993; 05-13-2018 at 06:19 PM..
Old 05-13-2018, 04:35 PM
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Everything is soft compared to carbide. I take it that you are replacing splined studs with through bolts during this process? Sounds like you're talking about the joint between the cats and mufflers?
I haven't pulled the exhaust of my Boxster (yet). So I don't know what lies beneath. If I were running into the same situation, I would consult Uncle McMaster (McMaster.com) and look at the drill bits I want, along with high temp anti seize and new hardware. I buy almost all of my hardware from McMaster, unless it's a need-it-today situation.
Old 05-13-2018, 06:32 PM
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When I did my engine swap I was sooo lucky not to break any of the exhaust fasteners. Mine were relatively rust free, still I put them back together with new fasteners and antisieze cream.

I had other stuff I had to drill out. I bought a new Irwin drill bit set, rather inexpensive, at ACE. I think it was about $30. You are correct, get the best drill bit set you can afford, start with smaller sizes & work up, use lots of oil and slow speeds on the drill. There may be some special tool for removing the flange bolt remains, but if there is I'm not aware of it. New, relatively high quality drill bits do make a difference. I've had good results with Bosch sets, too.
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Old 05-14-2018, 07:10 AM
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Well some success today.

I went to lowes and got a carbide multi material bosch bit and another cobalt dewalt bit.

The cobalt bit didn't really do much of anything. The bosch carbide bit slowly made its way through the remainder of the hole. Then I was able to increase the size of the hole with the bits I already had.
Unfortunately when the bosch bit exited the hole 1/2 of the tip broke off rendering the bit useless for the next bolt extraction.

Poking around the toolbox I found a pack of High Speed Steel countersink/drill bits that I had bought probably 10 - 12 years ago that I never used.

Now those things went through the next bolt like a knife in butter. So I was able to get through a whole bolt pretty quickly in about 30 minutes or so altogether.

I have to deal with the 2 studs that broke that are on the car still, I think I have a chance at backing them off as there is a nut welded onto the cat side. Only 1 of the pipe side nuts did loosen on the day I removed the exhaust, I may drill that one out.
Old 05-14-2018, 06:38 PM
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Damn these bolts. I moved on to the ones that broke on the cat side. I spent probably about 2 hours to drill out one and over an hour on the second one. These things are a *****. I have spent much more time than anything else on these rusty bolts.

Ironically the car doesn't have any rusty parts on it other than these exhaust bolts.

I used to own a 300zx that had previously been owned in Ohio, that thing had some serious rust issues. I did unbolt the exhaust on it and didn't really have any issues. I got lucky with that one.
Old 05-24-2018, 05:59 PM
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I drilled out the last one today. There was one stud left that actually unscrewed properly when I was removing the exhaust. Ironically this was the first one I loosened.
I was planning to leave that one alone.
Anywho, I picked up some drill bits this week at Lidl, the grocery store. They advertised HSS bits for $3.99 so I picked up 2 sets. Holy crap, I got through that bolt in only 14 minutes. I was completely surprised.

To recap, make sure you have a good set of bits. Start with a size about 1/8" and get the hole all the way through. Then work your way up to about 8.5mm.
Old 06-15-2018, 05:33 PM
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Drilling out rusted header bolts is one of my least favorite jobs. Glad you finally got er done.
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Old 06-15-2018, 08:31 PM
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A couple weekends from now I'll be installing a Remus cat-back exhaust.

What methods has anyone used to prevent breaking the muffler to cat studs?

In the past I've had good luck with Kroil (works best when it sits for a while), Pb blaster, a homemade mix of ATF and acetone, and heat where possible; I haven't tried the "wax" trick.

I plan to try them all since I do not want to drill out/press out any broken studs.

Thanks, any information is appreciated.
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Old 06-21-2018, 05:18 AM
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In my case, I don't think there was much choice. They actually all broke off relatively easily, much easier than I was expecting. So basically removing the muffler I broke 5 of 6, none of the others on the hangars had issues coming off.

Hopefully in your case yours wont be as rusted as mine were.
Old 06-21-2018, 05:27 PM
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Quote:
Originally Posted by johnsonj View Post
A couple weekends from now I'll be installing a Remus cat-back exhaust.

What methods has anyone used to prevent breaking the muffler to cat studs?

In the past I've had good luck with Kroil (works best when it sits for a while), Pb blaster, a homemade mix of ATF and acetone, and heat where possible; I haven't tried the "wax" trick.

I plan to try them all since I do not want to drill out/press out any broken studs.

Thanks, any information is appreciated.
Try letting some penatrating oil soak on them for a while. But get ready to break some. Get some good quality drills, just in case. If I've learned anything over the years, it's that you should only buy American made drills, or European. That goes for most cutting tools. Anything else is a gamble. I've been screwed too many times by not having good cutting tools. Basically, buy them from a place like McMaster and NOT home Depot. Sometimes the cheapos work, but when they don't, you'll be pissed. You're better off spending a little more.
The way exhaust hardware is heat cycled and exposed to air means that they often rust together. Adding some high temp anti seize at reassembly will help in the future if you ever need to break them back apart.
Old 06-21-2018, 06:23 PM
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Quote:
Originally Posted by M Baldwin View Post
Try letting some penatrating oil soak on them for a while. But get ready to break some. Get some good quality drills, just in case. If I've learned anything over the years, it's that you should only buy American made drills, or European. That goes for most cutting tools. Anything else is a gamble. I've been screwed too many times by not having good cutting tools. Basically, buy them from a place like McMaster and NOT home Depot. Sometimes the cheapos work, but when they don't, you'll be pissed. You're better off spending a little more.
The way exhaust hardware is heat cycled and exposed to air means that they often rust together. Adding some high temp anti seize at reassembly will help in the future if you ever need to break them back apart.
Fortunately I was able to remove my stock exhaust without breaking any studs.

I kept soaking them in Kroil, using a needle oiler while I replaced my plugs.
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Old 07-09-2018, 09:14 AM
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Quote:
Originally Posted by johnsonj View Post
Fortunately I was able to remove my stock exhaust without breaking any studs.

I kept soaking them in Kroil, using a needle oiler while I replaced my plugs.

I was just under my car putting in the new M030 suspension. I was looking at the exhaust hardware while I was there and I'm thinking I should hit it with some kroil too. I'd like to do a new exhaust next spring, and I'd like to keep the drama to a minimum.

Good to hear that you managed it without cutting or drilling. Drilling out bolts takes the fun out of just about any job.
Old 07-09-2018, 03:00 PM
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Quote:
Originally Posted by M Baldwin View Post
I was just under my car putting in the new M030 suspension. I was looking at the exhaust hardware while I was there and I'm thinking I should hit it with some kroil too. I'd like to do a new exhaust next spring, and I'd like to keep the drama to a minimum.

Good to hear that you managed it without cutting or drilling. Drilling out bolts takes the fun out of just about any job.
Yeah...I figured I would break something and have to drill.

Biggest trick was finding the right combination of extensions and swivels to get a proper grip on some of the nuts.

Installing and torquing down the new nuts was much easier - maybe because the new pipes to the mufflers did not have a "bent up" lip on the flange.
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Old 07-11-2018, 01:39 PM
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