Recently purchased a Tractor 11. Took it for a mow for the first time last weekend and whenever I hit a high spot or a rock (yes I know they should be avoided) the cutting deck belt comes off, flips and get's all tangled. It doesn't feel overly loose, although when engaged it does slip a little bit on the deck pulley.
Is there an adjuster to tighten it? Also I feel that maybe it would benefit from a belt guide at the front of the deck pulley, not sure?
Ummmm, that detail is not applicable to the tractor models............
The first thing to try is a new belt, of course. If that doesn't solve the problem completely, I've found the need in the past to put spacers behind the spring to 'firm up' the belt tension - especially if the deck is bit loose on its mountings. Beyond that modification of the system shouldn't be necessary.
Try a new belt first and see if that fixes it and if it doesn't we can talk more.
Forgive any errors or omissions, I'm doing this from memory - too llate to go to the shed now but I'll check tomorrow morning if I get time and correct anything I've missed then.
Pop the transmission cover (rear bodywork panel off by removing the bolt and nut securing the seat base. The tin work slides off. This gives reasonable access to the clutch/pulley bracket thing that you are referring to. There are a couple of slightly different variants of this thing. The early variant has folded sheet steel belt keepers around the pulleys and these are loosened or removed by undoing the pulley bolt at each pulley. The later variant has a welded pulley keeper arrangement that hinges open when the bolt on each side that secures it is removed.
There is also a welded style pulley keeper at the engine pulley. Loosen or remove this as required to remove/install the belt. Similarly there is a keeper at the deck pulley in the shape of a bent bolt that is loosened or removed for access.
Yup, your right there is a guide each side of the deck pulley as well as the bolt at the front. My apologies, I was working from memory- too tired and lazy to walk out to the shed last night!
The absence of the forward keeper could be part of your problem but my gut feeling is that it's not a huge deal. It should be there and popping it in will cover that base. Once belts start rolling over for whatever reason ( just an old belt or some other underlying problem), it'll keep doing it and need replacing. It's possible there is another problem such as looseness in the cutter deck mounting or height adjustment mechanism or weak spring tension but a new belt is the place to start by the sounds of it.