Blade belt jumped off mine when I engaged the blades on the first lawn of the day yesterday. Looked at it and I dont see any wear or marks on the belt so I laid down and put it back on. Worked fine rest of the day and again today. Not sure what caused it. I personally think the tensioner needs to be snugged up a bit.
2013 Gravely 460Z 29EFI
2011 Gravely 36GR
2008 Gravely 160Z
2004 Gravely 34Z
1998 Lazer Z HP 48 (old faithful)