Broken bolt in rear dropout

On 10/4/2008 10:48 AM A Muzi wrote:

Mike Rocket J Squirrel wrote:
The bike that I've recently repurposed as my town bike used to have a
set of fenders -- mud guards? -- on it. I took them off a couple years
ago, and when doing so I craftily broke off one of the mounting bolts in
the rear dropout. Don't ask. It wasn't one of my prouder moments.

We're getting some rain and it's time to mount the fenders. But I'm
staring at the face of the broken bolt. And it's not wearing a very
helpful expression.

I have a feeling that things are gonna get messy real fast.

So it's broken off flush with the outside of the dropout, and there's
nothing on the wheel side to grab onto. The bolt wasn't any special
hardened type, just the usual cheap and cheerful kind that came with the
fenders.

Most articles on broken bolt extraction are targeted at extracting
larger ones from engine blocks and such. Anyone have any advice on how I
should proceed with his little one?

Drill straight through on center with a 1/8 (3.1mm) bit. Try a screw
extractor. If still not, and if it is truly on center, follow with a
9/64 (3.5) drill. Repeat screw extractor. Clear with m5 x 0.8 tap and
use an anti seize paste next time. Even stainless screws in a small fine
thread are no help as adding salt water makes the end itself oxidize and
lock those in any way.


Hey -- worked as advertised. Easy as cake. Thanks.

@ Ryan: fortunately I have an automatic center punch. Getting a nice
little dimple on the face of the broken bolt was a piece of pie. I do have
one of those little Harbor Freight tabletop drill presses, but I wasn't
too interested in stripping the frame then figuring out how to lay
it--just so--under the chuck, so the work was done by hand.

The initial hole I drilled was 1/8'' (Dremel) as Andrew suggested. I used
a pilot tip bit. Nothing useful happened at this point and since I don't
have an extractor I opened the hole to 9/64ths (Dremel don't take a
9/64ths, switched to regular drill), and while some little sharp bits of
metal wanted to come out, they weren't real enthusiastic about it. Shy, I
reckon. So out came my father's old circa-1970 Chinese metric tap and die
set and its m5 X 0.8 tap cleaned up the threads real nice.

Fenders are mounted, and we'll see how it all works tonight. Riding
downtown to join Mrs Squirrel and a couple of her lady friends for dinner
then a play.

The only issue is that this is a road bike frame and I've got some 35-622
bumpy tires on it, leaving little fender clearance between the rubber and
the frame. I'll probably get some leaves stuck in there, but my son who
was in the Netherlands last year tells me that the sound of trapped leaves
and other street detritus rubbing on the tires is considered normal.
Apparently indicates proper operation. Warns others of your presence or
something.

Thanks, all, for the tips.

--
Mike "Rocket J Squirrel"
Bend, Oregon