Topic: Broken Tap Removal or: better living through chemisty!

[fantino]

Today I decided to take a look at the part of the split cases on my cb500 I've been dreading: a broken case bolt left from a PO :-(

On closer inspection it got a lot worse... it was a broken tap. A mangled, broken tap at that. Bummer. The edges around the bolt hole are pretty mangled as well.

[EDIT] I started applying a solution of alum (pickling spice) to the busted tap, which dissolves ferrous metals. It's slow goings, but is definitely dissolving the tap away. Unfortunately the case is too large for me to submerse into heated solution, so even slower. Once the tap is out, I'm hoping I can get away with an M8 helicoil to repair the very mangled M6 thread...

I've included a pic of which bolt is causing the trouble, though it's in the top case.


Out of curiosity, what is the feasibility of putting the cases back together simply missing this one bolt? Fine or huge oil leak waiting to happen?

[dave500]

err,it probably wouldnt leak,with saftey goggles on have you tried with patience knocking the tap in the undo direction,or even breaking it bit by bit,ive done this with luck.or getting pointy pliers ground down onto it,pain in the neck.

[fantino]

Yeah, I started out breaking the tap up. Worked for a bit, then it stopped breaking up, broke my center punch and started messing up the hole even more. The alum is definitely working, just real slowly. I'm hoping by the time I get off work tonight it'll be eaten away enough to loosen it out...

Since the hole is on the edge of the case, how much can I drill out for an oversize helicoil before the wall is too thin?

[kvallelunga]

Can you find someone with a carbon EDM (Electrical Discharge Machine)? They'll probably be able to burn it out for between $15 and 30 in about 1/2 hour. I would think you would want to use the M6 helicoil. They are oversize, the coils bring it back to the original size.

[dave500]

is the tap a four land type?the one i broke out was a three,,it more or less fell to pieces with carefull work.,yours might be a few more threads in than mine was.

[fantino]

3 land, broke off pretty far down the hole though. And unfortunately there's no one in my area I could find with an EDM machine. But on the plus side, Alum works!

I set the crank case half with the broken tap into a pyrex dish in a pot full of nearly boiling water and added a strong solution of alum and water into the dish til it just covered the tap hole. Left it on the stove and watched the tap bubble away for a while and it eventually ate enough away that I was able to just extract it with a pick and a pair of tweezers.

Overall the alum for the removal cost about $3. Less than any tap extractor, easy out or electric removal method I looked into, pretty harmless and almost no effort involved :-)

+1 for chemistry! I'll probably never extract another bolt stuck in aluminum again if I can get away with drilling it out halfway and letting alum do the rest.

[mystic_1]

That's a great tip, thanks!

mystic_1