Has anyone added a second belt to their VPI Scout

Since you have a SDS for your Scout, I would suggest replacing the VPI belts with a thread belt. I tried mono-filament fishing line (Spiderwire) and silk thread. I preferred the silk thread using a blood knot as I can get the knot to reduce to a smaller size.

The Scout motor pulley is tapered on both the 600 or 300 RPM motors. You can verify this on yours by using one belt and setting the speed, then move the belt to another pulley grove. If the speed changes, the pulley is tapered.

If I were to use two belts, I would ensure both are talcum powdered so I did not have too much noise introduced by buckling or slipping due to the different diameters of the pulley groves.

If it is the case that the pulley is tapered then my observation is moot, the speed differential would be due to the tapering. Etbaby originally reported that his pulley was not tapered.

An interesting experiment would be to try the dual belts on all possible combinations of grooves.

AFAIK every Scout pulley is tapered. It is not really noticeable with the naked eye, but it is there. I think this explains his speed differences.

With that in mind, I cannot see how this would lead to positive results as it would seem the two speeds would be "fighting" with each other.

More is not better in this case. Stick to a single belt and stop trying to reinvent what Harry spent years optimizing.

I have a spare belt for my Scout. I added the belt to the 300 RPM motor pulley and adjusted the platter speed. Everything was flat and dull sounding with the two belts. Popping one belt off restored the energy and dynamics.

Even if there wasn't a degradation of the sonic characteristics, I would not recommend using two belts on a tapered pulley.