Broken Crankshaft Bolt - Extraction How To

[66c10Steve]

Just thought I'd put this together for anyone stuck in the situation of having a broken bolt in the nose of the crankshaft.

In my particular case, the previous owner was removing the harmonic balancer remover/install tool when the bolt sheared off inside the nose of the crank - about half an inch before the threads start so there was no way to grab on to the broken bolt. I spent a fair amount of time searching the web and talking to people and it seemed like my options were replace the crankshaft, take the crankshaft to a machine shop and have them extract it, or try to extract it myself. I decided to try option 3 since it seemed like I had nothing to lose.

Step 1 - Gather tools: You'll need a hammer, a center punch, penetrating oil, a small container to hold the penetrating oil, a large adjustable wrench, a #4 screw extractor, a drill, and a 9/32 cobalt drill bit (don't even bother with oxide or titanium bits).

Step 2 - MOST IMPORTANT STEP - Grab the center punch and your hammer and get the punch as darn close to center of the broken bolt as you can possibly achieve and keep it 90 degrees to the crankshaft before giving the punch a couple good blows with the hammer. The reason this step is so important is because this determines the course of your drill bit and if you mess up the threads of the crank then you're going to have to retap the threads - which I'm not sure how easily could be done.

Step 2a - Lay some rags down below your work area - I forgot to do this but could have saved myself some cleanup.

Step 3 - Spray penetrating oil onto your newly marked bolt and fill up the small container with penetrating oil.

Step 4 - Drilling - The trick to drilling the hole successfully through the bolt is to not let either the bit or the bolt heat up too much. So start by dipping the end of your cobalt drill bit in the penetrating oil, then bring it in contact with the center mark that you punched, holding the drill as close to square to the crank as you can start drilling on low speed with decent pressure (don't try to push the drill through the thing but don't be a sissy about it either)
After 5-10 seconds pull the drill off, squirt the sheared bolt with a bit of penetrating oil and dip the end of your bit in the penetrating oil while spinning the bit. Repeat this step several times until you drill through the bolt - it took me about a half hour. Remember to be patient as you don't want to overheat the bolt or the bit.....if you see any smoke, immediately pull back the bit and squirt more penetrating oil on the bolt and the drill bit. Smoke is a sign that you're either pushing to hard or trying to drill to fast - so try changing your speed and/or pressure.
After you've drill the hole through the bolt (or at least deep enough to set the extractor) blow the hole clean and soak it all down again with penetrating oil.

Step 5 - Extraction - Put the #4 screw extractor in the newly drilled hole and give it a couple taps with the hammer to set it (don't kill it, just a couple taps will do). Grab your adjustable wrench and start turning the extractor counter-clockwise (it's a standard right thread) until you pull it out.

Step 6 - Cleanup - After you're done your happy dance, wipe away the penetrating oil and metal shavings as best you can and then blow the end of the crank clean with compressed air. Finally, if your threads did sustain a bit of abuse clean them up with a 7/16-20 tap.

Here is a link to items you'll need:
Screw Extractor: https://www.princessauto.com/en/deta...et/A-p8619454e
Cobalt Drill Bit: https://www.princessauto.com/en/deta...it/A-p8718900e