Yes.

The thrust washer is SOOO easy to loose.

[link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXCW52&P=Z]This one - Click me![/link]


It is thin, but provides the needed spacing to keep the drive shaft from hitting the backplate.

Without it your engine may not turn over and it may be damaged.