I have a national 8400 I use on a golf course. Last year the maintenance guy took the blades section off to get sharpened. When he put the rear one back on the belt on the tension pulley is loose when I lower the blades. When I bring them back up the spring gets tight on the pulley. It seems like something is opposite of what it should be. I was wondering if anyone if familiar with this mower and rear pulley ?