Charles Vincent wrote:

There are also several acids that will attack steel and not aluminum. I
have used that dodge many years ago to remove a busted tap from an
aluminum part that I had a lot of time invested in. I used plain
battery acid that time, but I think I recall that nitric acid could work
better. This would likely attack the valve seats and liner, but would
not harm the head or piston. You would want to degrease everything
before trying the acid.


On reflection, forget I said that. To much risk that the acid would
have some long term effect and I simply don't know enough about it to
recommend it for an aircraft part.

Charles