I purchased an 04 440 and have been reading about the slip gear which i assume is the 13 plate bottom gear on a 15 plate chain. I don't understand the reasoning behind this for one and for another the chain has walked out and chewed up the case cover. The gear doesn't move but the chain does. Can someone explain this to me and maybe point me in the right direction to cure the problem. Thanks

Not sure why your chain decided to move over, but the reason for the slip gear is because in the event of a power-on landing it simply slips off instead of exploding your case due to the rediculous amount of torque suddenly being put through it.