Step 1: Boil enough water to cover the part.
Step 2: Desolve alum in the hot water until it can't take any more
Step 3: Drop part with broken tap into water
Step 4: Soak at just below simmer for 3-4 hours
Step 5: Remove part and shake out tap.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"mkazemi" wrote in message
oups.com...
Hello
I have a broken tap in a 1993 chevy lumina water pump housing. the
housing is aluminum but i dont know what grade it is. i am pretty sure
that the tap is cast iron but im not 100% sure. the tap is broken off
right at the base of the housing and i have tried cobalt drill bits and
they didnt work. the drill bits stated that they will work on armor
plate, but i gues they were wrong, being that they didnt work in
removing cast iron. I was wondering how i should remove the tap, would
a diomnd bit help or is there some chemical that i could use?