I made one of these a couple of weeks ago but I have a problem. Whenever I get to the 3rd series and 6-8 reps into the workout, the pulley nearest to the weight locks up! VERY annoying! At first I thought maybe the heat was causing parts to expand or something like that but no, the wheel turns just fine. Im only using 38kgs and the pulley is rated for 20kN so weight shouldn't be a problem! Im really puzzled by this and it sucks big time cause it's holding back my lat workout Any ideas?