How to change drive belt - Al-Ko two wheeled tractor

[WhelpoWeeder]

Hi, I am looking for advice on how to change a drive belt in an Al-Ko COMBI BF 5002 R two wheeled tractor.
This particular belt runs from the cluster of pulleys at the front of the machine to the gearbox and provides power to the wheels.
The problem I have is that the pulley that sits on top of the gearbox has a cylinder nut each side to enable a covering plate to be attached, but they sit so close to the pulley that I cannot slip the belt onto the pulley.
I can't see any way of moving the pulley away from the cylinder nuts, either up, down, forwards or back, without considerable disassembly of the machine.
This seems counter-intuitive as surely the machine would be designed to enable simple renewal of drive belts.
If anyone has experience of these machines and can shed light on how to renew this belt I would be most grateful.
Thanks in advance.

[Mick]

Unfortunately I've not actually seen or worked on one of Al-Ko combi tool power units. I can see what you mean though, those rivet nuts look very close to the pulley. 

I'll have to see if I can find any info on this, though the operators manual will no doubt suggest that belt inspection or replacement should be performed by a service dealer.