Joined: Jan 2009
Posts: 44,338
Likes: 6,640
From: New York, NY, and High Falls, NY, USA
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
This could happen as a result of insufficient tightening. Something about the gap allowing the metals to fuse chemically.
Use more leverage and make sure you're turning in the right direction. You'll get them out. I've never used heat.