For anyone else considering taking out the primary mirror I suggest you follow Geoffs article on GSO dobs. Put the scope on the ground before unscrewing and removing the primary.
Unfortunately, I had not read the article. I was sitting on a chair with the scope horizontal and the primary facing me. When I unscrewed the primary and pulled it out I was suddenly wacked in the head with a scope that was now very top-heavy. If I had of realised how much a primary mirror weighs I would not have had this problem.
