Update: it seems the design in this area has been beefed up on later revisions of the Tina2 and Tina2S. If an inspection of the underside of your unit shows 8 ribs around the mounting for the Y belt pulley (rather than the three shown here), hopefully there is no need for action. It is not necessary to remove the pulley to see the ribs. See photo in this post (click).
The photos show the threaded insert that secures the screw for the guide pulley (see also viewtopic.php?p=1575#p1575). Note the cracking in the plastic pillar which houses the brass insert. I have no doubt it was this cracking that eventually resulted in the plastic breaking away and the insert no longer holding the pulley in place on my Tina2S, and I have no doubt this also accounts for other reports.
.
- IMG_4464.jpeg (160.13 KiB) Viewed 914 times
- IMG_4465.jpeg (82.07 KiB) Viewed 899 times
The cause is the (necessary) tension of the Y belt on the guide pulley, the pulley's axle being the screw through it and into the insert. The screw is only captive at the insert, which is off-centre from the force applied by the belt and therefore applies leverage on the insert. If it were not for this leverage, I do not believe the plastic would fail. To counter it, the plastic pillar needed to be designed thicker (the alternative being some kind of bracing at the other end of the screw, which would make assembly difficult).
A stitch in time saves nine (so the adage goes), and action while these are only cracks (or preferably before cracks appear at all) should be less difficult than after it has failed completely.
What to do? See next post, but if yours looks like this you probably want to stop using it...
(1)
(2)