Scag belt problems

[yaniaj1]

I have a Scag Z cat with less than 100 hrs on it.I have used the mower most of the summer with no problems.Lately when I start the blade the belt comes off the pulley .The belt looks great. Would the bolts that holds the blades on be too tight or a grease problem in the spindles be causing this problem.Any help would be appreciated .
thanks
Joe y

[steve45]

Sounds like an alignment problem, or perhaps tension. You should be running the engine at low speed when engaging the blade. Also, don't change deck height with the blade engaged.