bang your head I have a 95' zrt 800, last year I was hearing thumping when I hooked up hard. I thought it was the track hitting the tunnel so I tightened the track. Soon after I was hole shoting and the chain snapped appart. I installed another used chain and sprockets,they were thumping also. I took them back out and the chain and sprocket is damaged allready. Someone sugested maybe jack shaft bearing causing it. What do you think?