Does the front sprocket have worn or bent teeth? Or is it nice and shiny from metal on metal? The rear is usually aluminum, so does not shine like the front. I go through 2-3 chains to a set of sprockets. Crazy some say, but trials is different from all motor sports. We do not put thousands of miles on a set of sprockets, we put hundreds. Our wear comes from all the starts and stops and stress of ups and drops. We ride in dirt, mud and water. Slowly, and then zap a big rock. Which stretches said chain. Do you know Montesa recommends the 4rt piston to be replaced after like 60 hours? Most 4RT riders are still on the stock piston ten years later. Say it isn`t so!