<VV> Broken bolt in crank...

[Tony Underwood]

At 06:31 hours 04/25/2006, Bill Elliott wrote:
>Always go with your first instinct... as I was mounting the flywheel 
>on the engine I'm assembling, one of those special 11/32 bolts 
>didn't seem to want to go in right. I normally chase all threads 
>when assembling, but I didn't have one of the unusual size taps. The 
>threads on both hole and bolt looked okay and on like the third try 
>it seemed to go in easier (but still a bit tight for my comfort). I 
>should have stopped at that point... but I didn't.
>
>As I was torquing down the bolts, the head on this one popped off. 
>Now that I have disassembled everything again and examined the 
>situation more closely, it appears that the bolt is slightly 
>cross-threaded in the crank AND shows evidence of having been 
>"attacked" by an impact tool sometime in it's history...
>
>Now in 20 years of working on Corvairs I've never seen this problem 
>before. I do have almost 1/4" of the broken bolt protruding, but it 
>is in _tight_.
>
>Any advice on how to best extract it without damaging my crank?


Weld a nut onto the exposed stud.   Be generous with the weld.   The 
heat also swells the stud and helps loosen it.   With care and a bit 
of rocking, the broken bolt should back out without issue.



>Also, assuming that I have permanently damaged the threads (I did 
>just find and order the correct tap) what is anyone's experience in 
>drilling and retapping to 3/8-24?


I'd chase the threads first and see how the bolt fits.    You might 
try using a "rolling" tap (the one with a conical tip and no flutes) 
to reform the threads rather than cut through the current misaligned 
threads.   Use lots of oil.



tony..