If I were you, I would take it apart and inspect it after 50 hours, 100 hours, 200 hours ...
Make sure you measure (mike) the needle diameters before first assembly so you have a reference for subsequent inspections.
The major concern here is lack of lubrication. Next is the big  bigger diameter (shaft) thrust bearing.
If I remember correctly, the bigger ID thrush bearing have significantly lower RPM limits than a smaller.
I was using a 35mm ID (2mm needles) thrust bearing. No measurable wear after 100 hours. But did have spray lubrication and I never reached 6000 RPM. Mostly 5200 RPM or so.

Finn

sqpilot@earthlink wrote:

Hi, fellow rotary enthusiasts.  Attached are two photos of the thrust bearing mod performed on my 2.17:1 Ross PSRU. The fix was done by Dave Mix.  He can be reached at harborview@rivnet.net   As you know, each Ross unit is slightly different (machining tolerances, etc). Dave will measure your unit and recommend the best fix considering the shaft, end play, etc.  Given the amount of shaft/play on my unit, this was the best method of installing the thrust bearing. Some units will have enough room for two thrust bearings. I was very pleased with the quality of his work and the fast turn-around time.  When I find a good vendor, I like to pass it on. The cost for this mod was $225.00 plus shipping.  I consider this to be a small price to pay for peace of mind and reliability.  Hope this is of interest to other Ross owners.  Paul Conner, 13B powered SQ2000 under construction.