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1997 S 500
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Discussion Starter #1 (Edited)
How to remove stripped hex bolt?

Wanted to perform the driver-side oil tappet/guide replacement yesterday but was stopped early on, by a stripped Hex Bolt on one ignition coil. This car had only been serviced by dealerships and I couldn't believe they had left a stripped bolt in place. It was obvious someone had tried to use vice grips or something similar as the head of the bolt is pretty nicked up. These are the 5mm hex (female heads), so basically the bot is rounded off on the inside. I don't have a picture of the specific bolt, but here's what the good side looks like. Any suggestions on how to get this off? I'll be sure to replace with a new bolt.

Thanks.
 

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'14 E350, '07 CLK350, '01 SLK320
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Hit it with some penetrating oil (3-in-1, WD-40, or similar) let it sit for several hours or even overnight. Try the vice grips again. If that doesn't work, hit it with more penetrating oil and then get over to Sears and buy an appropriate sized easy-out.

When you but everything back together, make sure you use a dab of anti-seize paste on the bolts. You will make life easier for yourself (or someone else) next time.
 

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providing the head of the bolt still exist and is not too torn up, get a dremel tool (or die grinder) with a cut-off disc attachment. square the tool as best possible to the head of the bolt and cut an area of uniform depth across the head of the bolt. what you are doing is cutting a groove for a flat blade screw-driver to fit into. try not to go any deeper than the inside area where the hex key would bottom out. also try to use a screwdriver whose tip is slightly wider than the bolt head is.

if this doesn't work, you can grind the head off flush with the coil bracket, remove the other coil bolt and then the coil. with the coil out of the way, you should then have access to a small part of the shank of the bolt to grab ahold of (like with vise grips) and extract.

if that didn't work, it will have to be drilled and heli-coiled or time-zerked.

* take no offense when i say this, but the fact you have asked how to go about this repair makes me want to recommend that if it goes this far (drilling, tapping, heli-coil), try to have someone around who has performed that type of repair so all goes well.

watch out where any metal shavings go and, as mentioned by bobs, use anti-seize on your bolt threads (anywhere where dis-similar metal threads meet).

good luck.
 

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1997 S 500
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Discussion Starter #4
No offense taken - I'm new to most of this, so I'm happy to rely on the help of experts. Still pissed though, that the last supposed experts (dealer) screwed this up.
 

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1997 S 500
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Discussion Starter #6
Update

Managed to get the SOB out today by using a screw extractor. Had to modify the extractor by grinding off the tip, as it was bottoming out before the threads had a chance to do their job.

I was surprised at how much down force I had to put on the extractor in order for it to work.
 

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