Thanks for all the ideas for removing the two broken motor mount bolts
in the block of my old Volvo wagon. For your reference here's a summary
of solutions ranked roughly by increasing degree of difficulty, or
decreasing degree of luck.
0. Use some penetrating oil to pre-loosen the bolt.
1. If part of the bolt is sticking out, grab it with locking pliers and
turn it out.
2. Use the broken off bolt head, engage the jagged end of the broken
bolt into it's other half inside the block, and turn it out.
3. Use a sharp pointy tool (chisel, scribe, awl) to tap the bolt
counterclockwise. Often the remains of the bolt are jagged and will give
you something to catch, otherwise drill a real small hole to one side to
catch your pointy tool.
4. Use a bolt extractor. Center punch the bolt then drill a very small
pilot hole. Use a left handed bit for the larger hole for the extractor,
and if you're lucky the left handed drill bit will unscrew the bolt
before you get to the extractor.
5. Weld a nut to the broken bolt. If the bolt is broken below the
surface, drill a sacrificial bolt and screw it into the exposed threads,
then weld through the hole.
I had a moderate degree of luck. Not Geo Hahn level luck (#2) but maybe
because the bolts weren't broken by overtightening they weren't too
stubborn. I soaked them in penetrating oil before heading to the
hardware store, then used my new carbide-tipped scribe and a tiny hammer
to reverse the bolt that was broken about two threads deep. It was
pretty jagged and took a couple minutes to free up then it came out
quickly. The second bolt broke smooth and flush with the block and the
scribe didn't catch. At the hardware store I'd found a small diameter
dremel metal cutter wheel and used that to cut a screwdriver groove in
the bolt. It wasn't a great groove but the second unscrewed quickly too.
For reference, if I'd been less lucky I could have gone back for a power
drill designed for "close quarters" that would have allowed me to drill
the bolts for an extractor -- at Sears they started around $150. It's
good to know they exist, but I was lucky to need no more than $15 in new
tools and it'd have been less if could have found my old jeweler's
scribe from college. I couldn't find a neighbor with a welder so I'm
glad I didn't get to #5.
--
Steven Newell
Littleton, CO
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