Tapered piston?

Paulgibeault wrote:BTW, to answer the initial question. Yes, All Cox pistons can be used in ALL Cox cylinders. BUT.... how well they perform is the question. My take...you never REALLY know until you run them. As this letter states, too tight fitting & too loose fitting always runs / starts poorly, but there is a lot "in the middle" worth trying out...

Dale Kirns 2nd letter to Paul dated 9 Dec 93:

Dear Paul - You have put together a very informative article - esp. on the engine & fuel areas. I added a little note on the last page about the importance of castor oil. I never use less than 10% castor oil in my fuels.
In 1979 cox made a major change in the cylinder & piston sizes (except for the Tee Dee series).
1. Cylinder:
a) went to 2-slit exhaust to prevent a fire from starting from over priming
b) eliminated free port on 2-slit exhausts.
c) "loosened" tolerances on I.D. hone

2. Piston:
a) finish grind - no longer has a "taper" at the top.
b) "loosened" tolerance on O.D. of piston

Unfortunately, the Black Widow has both of the "loosened" tolerances in all engines. If both are on the "right" end (cyl I.D. on the small and piston O.D. on the high) you can have a fairly good engine. But the other way - very loose fit/poor compression/ hard restarts/ poorer performance. In defense of Cox doing these changes it was because the bulk of their engines went to "first time users" who didn't know anything about a 1/2A engine. "Rich" and "Lean" was a term they did not understand. So, by fitting the piston/cylinder on the "loose side" - and leaning the engine to max power (when new) it was less likely to stick.
Apparently, it cut down on a "few" returns, but mainly it cut manufacturing costs. Seems that is always the bottom line.
Good luck on this venture, Your off to a good start.
Keep 'em flying,
Dale Kirn
"and now you know the rest of the story...."