I have a "just broken in" ZDZ-40 which has developed a metallic clunk with each engine revolution. It is being returned to RCS and it sound to me like bearing slop or piston slap. Now, everybody is thinking that this idiot ran the engine without oil, but the engine was broken in with 40:1 non-synthetic oil then changed to 50:1 amsoil. The engine has only run on 1 tank of amsoil.

I want to share with you an email from Mike Dooley:

We will evaluate the engine and make a determination about possible failure. FYI, I personally do not care for the Amsoil. It is possibly the worst for carbon buildup I have seen. Very strange failures associated with this oil. We are puzzled and I can not recommend using it. And I have seen ALOT of engines.

We recommend the Pennzoil air-cooled or Klotz R/C Model lube syn, Belray
H1R, Honda HP2, Mobil 2 cycle syn, Red Line, Blendzall etc....at a ratio of
40:1 FOR THE LIFE OF THE ENGINE. (this is a new recommendation as of May 2004).

Mike
RCS

I would bet you simply are hearing the rotor seat - all of em do this when turned over -especially turned backwards.
The rotor is large in diameter and the
"slap" sound really carries .
sometimes at an idle the sound can show up - basically just a bit too much rotor to backplate clearance -
No big deal--part of being a disc rotary valve.

Dick,

I do not believe you are correct. I have 13 of these engines and this one is the only one with the noise. It is really bad when the engine runs.

Elson