There should be a lug on left side of frame to prevent swing arm spindle turning. Its seized on the inner tube so it gets really difficult to remove. try removing the grease nipples first and cleaning them out. then put 'hose' end of PB Blaster can into swing arm and soak the inside. If that doesnt work you have to lay bike on left side and beat the pivot until the frame flexes slightly. then you use a hacksaw blade with end taped up as a pull saw in the narrow slot.(remove it from hacksaw frame) When you have one side cut you can move swing arm to other side and repeat cutting process (Tape the 'arrow' end of hacksaw blade where it shows cutting direction and pull it towards you, good idea to fit a short bolt, nail or whatever in the normal mounting hole as well)
Done way too many bikes like this, not just Yamaha's (in fact, mostly Honda and Suzuki)
