The History Man":1opqoxgi said:
Is it seat tube or down tube?
If seat simple. Long metal tube down inside to press on rivnut ? Obviously both need to come out if it’s bottom one.
Those metal broom/mop handles? That kind of thing.
I would give this a 1% chance of working and a considerable more chance of doing frame damage.
A riv nut on a bike frame is typically some soft AL and round - just like a pop rivet (not hexagonal); so having a
sufficient grip by just applying a down force to it's smooth side is a tall order. It
will spin around. The problem
is due to corrosion on the bolt and riv nut inside the frame, the longer the bolt and riv nut the chances of
more bonded corrosion increases, and hence more force will be required to remove the bolt.
What you want is to try and preserve the riv nut in position; at least to start with.
Attempting to drill it out will most likely make it spin more and start to enlarge the hole in the frame which
will make a subsequent riv nut be loose fitting. There is also a real world problem of having enough space for
the drill and drill bit to position it on axis.
The best advice above was to carefully Dremel the sides, fold the edges and punch it out; personally, that
would be my next to last resort for a AL frame. The last resort would be to weld it in place!
I have seen whacked out advice of using super glue - how that can be applied properly to
an unaccessible part and not making a mess is a mystery. I wouldn't trust super glue on Ti, Steel or AL, especially
not knowing if the parts I want bonding are either oily, rusty or corroded.
BTW the OPs problem is the down-tube.