Broken Exhaust Stud

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drak130
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Broken Exhaust Stud

Post by drak130 »

Hello All,

Got the mufflers off for flame cone repair and noticed evidence of minor leaking around the flange at cyl 2 and 4. Soaked bolts for two days in Kroll, thought I was home free when the inside bolt on cyl 2 snapped off reinstalling new gasket (17-19 ft-lbs of torque per the lycoming table). Tried some vice grips initially to back it out with no luck. Also based on that stud snapping decided to replace all the studs on both cylinders. Tried double nutting with no luck. Anyone out there have better techniques? A bit stumped here.

Thanks
Tim

Kirk
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Re: Broken Exhaust Stud

Post by Kirk »

Had a tractor repair done recently on a broken stud. Hit it with penetrating oil daily for a week. My mechanic welded a nut to the stud. After that, he spent a long time tapping a box end wrench to loosen the stud. He’s a patient man, spent 40 minutes on it.

He explained that the light tapping worked best for breaking seized threads. I was impressed, came out clean after being corroded and threads stressed from a massive pull that sheared the bolt head.

Kirk

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DavZeeMXT
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Re: Broken Exhaust Stud

Post by DavZeeMXT »

There’s lots of YouTube videos using different techniques. Maybe you’ll see something there that can work for your situation.
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bentmettle
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Re: Broken Exhaust Stud

Post by bentmettle »

If you have enough room for double nutting, you are in a better position than I usually find myself in.

First off, I'd try the "maybe I'll get lucky" and go with a small plumbers torch around the stud and see if I got any motion on the double nutted assembly.

If that doesn't work, Since you can double nut it, if it's clean, you can usually get both nuts back on it again, and leave the 2nd one proud of the broken stud so that there is a pocket inside the nut, with the broken stud closing out the bottom. With a MIG welder, you can weld the nut to the stud by filling this pocket and get some decent surface area.

Once it's cooled so it's not cherry red anymore, you can try backing it off with a wrench and sensible force. Don't go too nuts. The heat should help you, but it's possible to pull the threads, too, if you just man handle it.

Hale-Yes
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Re: Broken Exhaust Stud

Post by Hale-Yes »

As a farmer, I'm always breaking the studs off of something. The procedure that I use to remove a broken stud in aluminum, cast iron, or steel, was taught to me when I was a high school kid by an old blacksmith who's shop I used to hang around. If there is some amount of stud extending out of the hole, place an oversized nut over the stud, and with with a mig welder set hot, weld it to the stud, filling the hole in the nut flush with new steel, getting the nut very hot in the process (translucent yellow).Then let it sit until cool to the touch. The very hot nut will transfer heat to the stud, expanding it and the threaded hole. The stud then cools and shrinks, breaking the tight bond and very often allowing you to put a wrench on the nut and work it back and forth, take it easy, with a little penetrating oil, you can slowly back it out. Works 90% of the time. If the nut breaks off, just repeat. This method also works on studs broken off flush about 70% of the time. If all else fails, grind the end of the stud flat, center punch it and drill a small hole in it, allowing you to hammer an 'easy out' (mis-named, not easy) in to it, and screw it out. BTW, the stud will drill easer if you have previously tried the welded nut procedure, as the heat from welding the nut on to the stud removes much of the temper from a hard stud.
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Re: Broken Exhaust Stud

Post by Dale Smith »

Hale-Yes, I have had good luck with the same thing you have just described. I have had alright luck with getting studs that are broken a little ways into the hole by putting a fender washer over the hole and welding that to the stud first. As long as it cast of some sorts the weld will not stick to the cast. Then weld a nut to the washer. If the stud was broken when you found it (ie Not clean and rusted up) it might take a couple of tries before the weld sticks to the stud. Last resort is an Easy out fallowed by drill it out and tap it. Just be care full and take lots of time with all of it. Hopefully it turns out to not be anymore than about a 3 beer project...

Best of luck!
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andy
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Re: Broken Exhaust Stud

Post by andy »

Good luck with the broken stud. I've never had to deal with one. Was the exhaust leakage around the cylinder flange or the exhaust header?

If it was around the exhaust header, I have some experience with that. The sign is that the underside of the cylinder is gray. The leakage comes from a deformed exhaust pipe where it connects to the cylinder header at the slip joint. Vibration and engine movement during start and stop can eventually deform the exhaust pipe and allow leakage. I didn't realize that it could be fixed by re-forming the pipe with a clamp until I had to have it done in Idaho in 2016. The exhaust pipes shouldn't fit too tightly on the headers at the slip joints or it may cause cracking or aggravate the deforming. Four cylinder engines are more prone to this than 6-cylinder due to the increased vibration, but it can happen on 6-cylinder engines as well.
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gdflys
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Re: Broken Exhaust Stud

Post by gdflys »

Andy, I have two header slip joints that are leaking. I'm currently doing my annual and will try that technique. I also bought a pipe expander to try and make sure the inner header pipe is perfectly round and may even slightly expand it. Hopefully doing one or both with reduce the slip joint leaks. Thanks for sharing the tip.
Greg Delp
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drak130
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Re: Broken Exhaust Stud

Post by drak130 »

My leak was around the exhaust flange. With the mufflers off and being repaired, I took a close look at the flange/gasket area and noticed evidence of leakage at cylinders 2 and 4. The inboard stud on 4 looked pretty bad so spent several days hitting it with Kroll. After all the horror stories imagine my surprise when it and the other bolts came right off!

Thinking I was home free I went about reinstalling new gaskets. In the fading light I thoght I had set the torque wrench to 18ft-lbs but had actually set 28. Snap went the inboard stud on #2.

Good news is my outstanding A&P came by Friday and with a propane torch and some sort of tool that he hammered onto the exposed stud it came out in about 15 minutes.

New gaskets installed using the correct torque.

Two lessons:
1-Never be in a hurry or get destracted by a talkative hanger mate while working on a plane...ie double check the torque settings

2-You never know how things will end up when you start taking things apart. This started with Maule SB-23...checking the tailpipes. Isn't there a country song about one beer turning into a family?

Thanks for all the advice from all that responded. Thankfully heat worked. Next was welding on a nut.

Cheers
Tim

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