marty said:Look.
Sheldon Brown / Traditional Thread-on Freewheels
https://www.sheldonbrown.com/freewheels.html
Punx0r said:I assume you're trying to save the threaded adapter?
Grip remains of freewheel in vice with soft jaws (or blocks of wood) and use a pipe wrench on the collar of the adapter. If you suspect a thread locking compound has been used, first heat the assembly to >100°C.
If that doesnt work you have to carefully cut through the remains of the freewheel (taking care not to cut deep enough to damage the adapter threads), then split it with a sharp chisel.
Punx0r said:I guess the dynamic torque from your drive motor is doing it up very tight.
Now you have two opposing slots can cut in the face, can you weld a large nut to a piece of flat steel inserted into both slots and use an impact wrench?
amberwolf said:you still haven't tried the one nearly surefire way to get it off: cut the freewheel itself. you use a dremel or similar, and cut thru the freewheel all the way to the threads. because of the adapter's flange, this will be difficult for the part that intersects it, and you'll have to grind the freewheel's own flange down at that point to avoid damaging the adapter. if possible, don't actually cut into the adapter's threads--the freewheel should be loosened enough just by cutting down until you can see the top of the adapter threads. (or made fragile enough to break it off at that point).
short of that, you could cut the edges of the round outer flange of the adapter itself so that it matches the hexagonal pattern of the largest and longest wrench that could overlap it completely, then use that wrench to take the adapter out of the freewheel, with the freewheel core clamped in a vise.
if the freewheel won't stay clamped, grind *it* to have flat sides, too, for the vise to hold onto.
then when you install the adapter into the next freewheel, make sure you thoroughly grease the threads of freewheel and adapter; this will make it at least a little easier to get it out next time.
judging by the scarring on the adapter, the likely problem with getting it off is that it's such a soft metal it is deforming into the very hard freewheel threads; the grease will help with that but not as much as it would with a hardened metal on both sides.
Punx0r said:OK, here is what I would do if you have no welder and how have the drilled holes:
Get a small offcut of steel plate 6,8,10,12mm thick
Drill a 1/2" hole in the centre and file square to take a socket wrench drive
Drill and tap two threads corresponding to the drilled holes in your adapter
Tighten down some shouldered bolts (preferably 10.9 or 12.9) in the plate and cut to length
If the adapter is not too tight may be OK having the bolts/pegs span the recess from the outer adapter face to the inner face (this will cause a large bending force on the pegs). If the pegs bend you will need to add some round spacers to fill the gap - either make a steel disc the correct size with a hole saw or find some washers close enough to the right size.