=================================================================================Torsional vibration, whirl and misc flex can do all sorts of weird and unpleasant things. Not all two strokes used in aircraft were designed to have a prop hung on the end of the crank. Some are fine, others are not. A lot of direct drive car engine conversions need an extra bearing to be reliable.
You state what a PSRU can do, but not How it Solves these 2 Stroke Engine Problems! Could we use some New PSRU's today, Yes. There are very few made today. Rotax has already dropped the A Drive, and for the 582UL the Drive of choice is the C or E Drive, it's only a matter of time for they drop the B Drive. Nobody that I know of makes a New Belt Drive for the 185UL or 277UL. ACE Aviation $560 says they make one for 377-447-503, but have a 6 month wait period. There is a guy advirtizing on ebay $950 some Belt Drives for 377UL - 582UL both Pro4 and Pro8, Challenger $1250 has a Belt Drive for a Pro8 Case.
I just never seen a PSRU that Solved any 2 Stroke Engines problems is all. I have seen Belt Drives cause some 2 Stroke problems though. Over tightening the Belt has melted the PTO Seal and the Crank Bearing Plastic Retainer. That's Why, you should only use Crank Bearings with Steel or Nylon(Best) Retainers.
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