Just purchased a Tange square taper cartridge bottom bracket. I've only installed the Shimano with the plastic non-drive side cup. The Tange comes with a metal non-drive side cup on the cartridge and I can't seem to get it off for installation. It rotates, but when I pull on it, it doesn't budge. Am I just a weenie or is there something I don't understand about removing the cup on this bottom bracket?