Had an issue over the weekend with my 455 Rancher. The chain jumped off the bar as I was finishing up a cut. I did notice that the end of the bar started to smoke so I already know a new bar is in order. My question is about the chain brake. I reassembled the chain and the chain will not move. The chain brake is flopping around and does nothing. I assume it snapped a spring or something and became fixed in the locked position. What do I need to replace to make the repair? While I am in the process I would like to upgrade to a 20" bar. Thanks in advance for your help!