Belt will not stay on pulley shaft

[Logon]

You misunderstand the design, the platter and pulley is fixed on the same level. Platter does not move in relation to pulley when outer platter is fitted.

Please note that I currently own a Thorens TD 321 Mk II and am not a turntable technician, but I can say that a belt/pulley system working without the considerable weight of the platter (3.2 kg) is working outside of the design specification and therefore not in optimum conditions and therefore the results are not very significant. IMO

 

[percival007]

You misunderstand the design, the platter and pulley is fixed on the same level. Platter does not move in relation to pulley when outer platter is fitted.

Sometimes, when pulley/belt is poorly adjusted, it can be benefitial to see what happens when the outer platter is fitted and extra friction added at startup, so upside down can help.

I mentioned pulley position, when you replace the pulley, it can be set too high or low, which can be a problem for the belt position. 0,5mm too high or too low pulley can lead to belt issues.

Regarding the PDF by Logon; not an official Thorens document. There's too many belts to say all are too tight, in my experience they are not.

Are you sure?
This video (not mine) shows the Motor mounted to the Plinth and the Platter and Arm suspended using Springs on a separate 'Sub-Plinth'. As usual on most Decks.
If yours doesn't move separately, perhaps you have the Transit Screw (if this model has one) still in place.