was pondering this half an hour ago when swopping out a worn drivetrain. It's like a burny/chemically smell just as the bolts come free - I guess it's heat from either a little corrosion, or threadlock or whatever has bonded them in the 18 months or so they have been done up, being released ?
......or maybe it's just me !
definately ain't shite - bike is always clean when I am working on it !

