Removing A broken bolt

If you turn a wrench on an old bike for more than 5 min you bound to find a broken bolt, stripped threads, or rounded fasteners. We’ll be removing a broken spark plug from a head. A few of the things working against us here are: Dissimiler metal corrosion with the plug being steel and the head aluminum,the fact that this head hasn’t been on a running bike since 81′ ¬†and was sitting in upstate ny it’s whole life.

As you know my cases and heads are out in Oregon getting vapor blasted. Guy sent me some pics and they look great. Bad thing is the $6.50/hr truck unloader at fedex doesn’t give a shit about my parts and they arrived In Oregon with a broken fin. I had an extra head but it still had this broken plug in it and I had tried simpler methods of removing it weeks before to no avail.

Theres lots of ways to remove a broken bolt, but my favorite is to weld a new bolt to it to allow use of a socket and the bonus of this method is the added heat cycling from the welding itself. First I drilled the old plug out to the same size as a junk bolt I had, this case it was 3/8. This allowed me to put the bolt in and get a good weld on the freshly drilled metal.

Underside of head with bolt welded to offending plug

Top of new "spark plug remover tool"

At This point I heat cycled the head a few more times with a propane torch for extra piece of mind and went ahead with the removing. As you can see It came right out first try.

Plug remover with the threads of the old plug visible on the end

I was ¬†pretty pleased that it came out easily without damaging the threads badly. Since my tap and die selection is pretty weak right now and I didn’t have the correct plug thread tap I did the next best thing. This works especially well for the CEI and WHITWORTH fasteners because I don’t have ANY of those taps. I found an old spark plug and coated the threads with valve lapping compound. Slowly I threaded the plug in by hand working it in and out. Removing all the crud and corrosion out of the threads from 30 years of sitting. Plug now goes in and out freely.

All that's needed for the trick

If you are ever in going to get some Vapor Blasting done. I HIGHLY recommend Jeff. First class dude

One thought on “Removing A broken bolt

  1. Good tip on the valve lapping compound.
    I use small brushes, wd40/solvent and compressed air to clean up threads, running the bolt in and out incrementally further each time.
    Never thought to use compound!

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