I have a John Deere 535 Round Baler. It bales good for awhile and then breaks the baler pickup chain. When I replace the chain with a new one it is too short unless I add a half link. This leaves the chain with too much slack in it and it jumps a cog once in a while on the sprocket, which eventually leads to more chain breaking. There doesn't seem to be an idler tensioner on this chain. What should I try?