Now that torsional vibration is being discussed let's get back to the
 single rotor version. Does anyone know what would be a satisfactory
 torsional vibration damper for these as they don't have the
overlapping
 power pulses from the other rotor to smooth things out i.e. how much
 flywheel do they need?
I note that Richard Sohn uses a Hirth reduction box on his - I think
 they use a rubber dough nut like the Rotax 2 stroke reductions?
Are the rubber isolators used by Tracey suitable for the frequencies
 of a single rotor, let alone the increased amplitude with no
overlapping
 power strokes?
It would be nice if the collected wisdom on single rotors was
available
 in one place, after all about 100 to 120 HP (Rotax 912 to 914
 territory) is commonly needed for very light aircraft. I must admit
 I'm not all that impressed with my 912, it only has 29.9 hours on it,
 the fuel pump failed - leaked oil, coolant seems to ooze out
 everywhere, and after all it still has exhaust valves to fail. I've
 just discovered a pinhole exhaust pipe leak that was burning the
 paint on the engine mount, it's not that far from fuel and oil
 lines. Just what I need, an in-flight fire:( I think my old Subaru
 E$A 81 is better engineered and cheaper.
John Evans
 (Heretic)

I think you are going to have to make your own.
 Tracy's system works well for a two rotor but a one rotor
 fires half as often. Tracy's system allows the engine to idle
 down to 1500 RPM. That should be your target idle RPM.
I would use his general design and increase the diameter
 of the rubber bushings and use a lower Durometer rubber.
 Silicone rubber is called for as it has a higher heat tolerance.
 A lot of heat will be going into the rubber.
 You can make the bushings out of silicone rubber sheet
 from McMaster. Allow a bit of expansion room.
There may also be an off the shelf off road rear wheel
 motor cycle part that might work.
The Centeflex is too stiff and they don't make a much softer
 one.
Paul Lamar

Don't forget that the rotors still have longer time per cycle than a
  piston
 engine. 270* instead of 180* that helps torsional vibration.
Check Chrysler products for a damper similar to the one in
  Attachement 4. It
 is used on the drive shaft instead of a U-joint. Chrysler 300, Jeep
  Gr. Cherokee.
Dale Davies

Generally that type is too stiff. The have a resonant frequency around
 2000 RPM. A two rotor is firing 4000 times per minute or
 66 CPS or 66 Hertz in the metric system. The one rotor would
 be half that.
Paul Lamar

Paul,

  Still fiddling with my single rotor.  Will send pics soon.
  It's removed from the plane and dangling from a hoist at the moment.
  Don't want to tear into it before getting an accurate weight.  A hanging
  scale is on its way.

  As mentioned earlier, the initial running of the engine was very rough.
  There were a few tantalizing moments of smoothness, where it almost
  seemed as though the engine was off, but overall the vibrations were a
  match for something with a broken propeller.  Less than a minute at idle
  managed to crack my exhaust plumbing in four places, and crack the
  engine mount as well.  The engine is mounted plugs up.  Engine mount is
  hard pointed to the engine, with rubber biscuits at the aircraft
  firewall, similar to volkswagen mounting for a Q2 airplane.  I added a
  little tubing to the mount for vertical loads, and it was one of those
  tubes that broke.

  I have not been inside the engine.  Lou Ross built it a long time ago,
  ran it for eight hours, and pickled it.

  Will take your advice and thoroughly clean the tbi.

  Also planning to completely disassemble the engine and see what is going
  on.  Will have it P-ported.  Considering aluminum end plates if the
  overall weight is much over 200 lbs.

  Engine mount obviously needs work, too.

  A while ago you sent a drawing of the Ross redrive modified with
  a thrust bearing.  Could you send those drawings, please?  I guess that
  needs to be done as well.  My gear ratio is 3.17:1

  Lewis.

  Assuming it is balanced properly and the mixture and timing are right
  it will be very rough below about 3000 RPM. Think of a one
  cylinder huge 1.3 liter 2 cycle piston engine.

  Paul Lamar