That was my thought as well. Assuming you've measured it right, dataMarshall has posted suggests that the chain should have failed long ago. And when a chain fails on a 616, it fails rather spectacularly. You couldcount the number of teeth on the gear as you turn the engine to figure out how many degrees each tooth is worth.
TFM is quite clear about a tooth being 18 degrees. (I looked it up.) It's a mystery! -- Jim
