VolvoHordz;119129 wrotehmm if memory serves me correctly there is something about shimming in the green books...
You can shim the crank pulley to change the width of the V (and therefore belt radius). In my case that one was okay (belt tension was good).
Last night I actually swapped the Bosch belt for a Gates belt of the same size, 13A0925. The Gates belt runs a deeper "V" shape than the Bosch, and has not suffered from the rolling over problem.
Now that I've spun my compressor up, it doesn't seem like it's moving any air through the inlet/outlet ports, which suggests I may have cocked up the rebuild in some way :|
Luckily I have the compressor from Nina's old B23E, which is also a York 210, so I'll drain that one and fill it with PAO 68 (hopefully I still have 200ml in the bottle) and go from there.