Gabriel,
Sorry hear you are still struggling.
From your previous post, I assume that the exhaust is off the bike and you are just trying to remove the 4 individual header pipes from the muffler. Does your exhaust have the pipe clamps on the muffler collector? There are exhausts out there that do not use this clamping arrangement. My first K had the clampless variant - my current two and my two spare exhausts (one off donor bike and one that came with Gretel) all have the clamp variant.
I had to replace the exhaust on Gretel yesterday - the muffler had been previously repaired but the repair had now rusted/burnt through and needed replacing with the spare that Stephen had provided with the bike back in August.
Before I removed the exhaust, I loosened the pipe clamps and tried to separate the muffler from the header pipes - but nothing would budge - hence the whole exhaust had to come off. A
massive thank you to Stephen - SGMayhew for his care and protection of the header studs and nuts - all came off very easily!
(Phew!!)
Once the exhaust was off the bike, I set about removing the header pipes from the muffler. With the pipe clamps totally released, the pipes still would not budge - even with some hearty hammering. As Charlie mentions, with the exhaust off the bike, it is hard to hold it still. The obvious solution came to me overnight - increase leverage. With the exhaust lying on the garage floor, I inserted a steel bar in one header pipe (extension bar from ½" socket set) and another steel bar in another header pipe (handle from my trolley jack). By standing on the extension bar, I was able to stop the exhaust from turning while pulling hard up on the jack handle. With some screeching of metal, the first pipe started to move. Wiggling the jack handle up and down, soon freed up the stubborn pipe. I repeated this process for all 4 pipes. Once all pipe could be twisted fairly easily, I then bashed each pipe with my wooden mallet while continuing the back and forth twisting of the pipe with the jack handle. All pipes were successfully removed from the muffler collector - and without any damage!
Photos for clarity...
Nothing but carbon and other combustion products were acting as the glue. I didn't need to use either heat or chemicals - perhaps I was lucky, but the increased leverage definitely made a big difference.
Replacement exhaust went back on bike without any problems - new copper gaskets in header, but original studs and nuts (all undamaged). Slackened pipe clamps and gave all header pipes a bit of a wiggle before fitting - once fitted and header nuts torqued up, re-tightened the pipe clamps. Being able to move the individual header pipes actually made fitting to the engine block a little easier.
Now, I wonder where I could get someone to weld a stainless steel plate over the hole in the old muffler? Is it worth it??
Good luck with your challenge.