John deere f72

[Frantic fox]

Hi all, I have been working on a john deere ride on mower, I have had to weld the deck back together as it was in poor condition and now looks a lot better than it did, I put it all back together again and when I engage the cutter the belt jumps off, any idea why?
it has a new belt as the original it came with was snapped and the last owner told me that the belt sometimes comes off, but I cant see why it would.

cheers

[Mick]

These have always been plagued with belts throwing of as far as I remember, even when they were badged as Honda. I seem to recall the hydro models were worse for this.  I'll be honest and say I can't remember what the fix was

Such a short distance between front and rear pulleys that any height of cut adjustment throws the alignment off massively.   Try setting the deck height to make front and pulleys more aligned before engaging the blade.