I have 5 of the OS55AX's, Two I fly regularly. All 5 have the same type thrust washer. On all 5 of my engines the thrust washer's fit is real sloppy, The notch cut is oversize letting the crankshaft moveside to side inside the thrust washer. no matter how tight I tighten the prop nut it will pop when I grab the spinner and flip it backward against compression to start it.
Am I the only one to have this "problem" and what can I do about it so that it fits tighter??
Great engine by the way.
Fred</p>

The "thrust washer" goes between the drive washer and the front bearing.  It only provides separation, it does not prevent any movement.  If your crankshaft has radial movement in the bearings, then you have either or both of the front and rear bearings going bad.  At any rate, if the crank moves radially in the bearings, then you need new bearings.

Ok, Let me correct my description and say it is the prop drive washer, not the thrust washer, that has the notch machined in it that is too big.
 http://www3.towerhobbies.com/cgi-bin...LXGCU9&amp;P=Z
   There is space between the flat on the crank shaft and the flat on the drive washer and this lets the drive washer move. The noise it makes is a snap or sharp crack when using an electric starter or flipping the prop backwards against compression to start the engine.
 All 5 engine prop drive washers and one replacement part are all this exact same way.
 Fred