what qualcast is it? they make/made dozens of models cylinder and rotary,petrol and electric. but if your on about a rotary mower turn it on its side (carb uppermost if petrol and ht cap off) then jam a lenth of 4"-2" up the channel that the grass uses to get in the bag that will stop the blade moving as you try to loosen the bolt(they are made to tighten rather than loosen in use)but if i was you i would find a friendly mower shop to do it for you :) i do them every day for customers while they wait and for nothing,it takes seconds with a air hammer they always come back, but its nice if they get it sharpened and balanced at the same time (or replaced)i dont know where you are but its £4 to sharpen at our place
benadams
August 2008