Here it is.... A copy and paste of the original post from 2003:

Well, as I had mentioned, my 16cc Kioritz powered Big Low Stick was a little underpowered here at my new location with a field elevation of 4200' and temps near 100 degrees. Engines lose power at the rate of about 3.5 per cent per thousand feet elevation. That was enough to take my Stick from being a nice flyer to being rather doggy.

So....

I had a Kioritz 21 cc cylinder lying around, and I decided to adapt it to my 16cc crankcase. The bolt patterns, crank stroke, rod lengths, and piston compression heights are all the same. The only difference is the wrist pin sizes, (and of course the bore size). The wrist pin in the 21cc piston is about .060" larger. I used some 6061 T-6 aluminum tubing to make bushings for in the wrist pin bosses in the piston. This would have enabled me to use the stock, 16cc wrist pin, except the pin was a bit too short. So I used part of a drill bit to make another wrist pin with the original diameter, but the longer length of the 21cc wrist pin. The wrist pin retaining circlips were a bit narrow to retain the smaller diameter wrist pin so I added washers trapped between the new bushings and the keepers to be sure the wrist pin was well retained. I also had to make up a couple of small spacer washers to place on either side of the con rod for spacing. The only other modification was to bore out the crankcase where the cylinder fits in a very small amount. This was only about .030" and only about 1/4" deep, and I did it with a dremel and a drum sander tool.

All in all, it was fairly complicated and I don't recommend it unless you are very handy, or a machinist, but it turned out really well. I rather did it as a challenge, and because I had the parts and the need. It turns the same prop 800 rpm's faster than the 16cc did. That definitely makes the difference in how the model flies!! Hope you find this all interesting...

Take care,
AV8TOR