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David Kerzel,     Pompano Beach, Florida

9 Cylinder Radial CO2 type compressed air engine with a rotary valve  First posted 7/8/2005

1/15/2007 Finally it is time for Cabin Fever and it is done, well built but does not run yet.  It appears there is a speck of grit in the engine that sticks every few revolutions.


I entered the Wright J5 Whirlwind in the Sherline Challenge at NAMES 2008 in Toledo and took first place.



For about 2 years I have been working on small compressed air engines.  It has been my goal to have the last engine in the series be a radial.   I began by researching models in the gallery and plans from S.I.C. Magazine.  Then I started researching real engines on the internet.  What I learned was most of the models had tremendous amounts of detail missing or simplified away.

I started with a single cylinder and try to get a reasonable amount of detail for the scale.  Part sizes were reduced again ending up at 1/24 scale as a target.  Old techniques did not perform well.  Fixtures were essential for everything.  Most parts took several attempts.  My R-100 project show some of the progress

Crank case.  When I was working on this I had a broken wrist and I did not get the chuck tight enough and it popped out and got a few dents.  I decided to finish the part any way.  It ended up with 2 broken drills in it but it is to print.  It is very helpful to see the real part and be able to make minor adjustments before the final one is made.

  These disks will be the master rod.

I have started on the full radial.  Drawings are mostly dome and several parts are under way.  Parts are still small and new techniques are still being needed.  The first build is not going to produce a usable set of parts but it will be a testing path for techniques.

9/13/2005  It has been a few weeks since I have worked on this.  The challenge is back.



The set of 9 pistons and connecting rods on a disk which is part of the master rod.  9 pins are soldered to the disk as wrist pins.  They are tapped for screws that will attach a second disk to sandwich the connecting rods in place to make a complete assembly.




The crank shaft has a large counter weight to balance the weight of the disk shown above.  The hub that will mount the prop is also shown.





Cylinders and liners are lapped and ready to go.




The big part of the master connecting rod on the crank shaft.

The camera is not doing well with this size parts and I am not motivated to get the other one out.




The crank shaft in the crank case with the big part of the master rod.

It is time to make a second crankcase with no broken drills so the cylinders can be mounted and the pistons inserted.  I could do it now but 9 times 4 tapped holes is more than I am willing to do, just for a test.  Wafting to see the master rod move is almost as exciting as getting ready for the first run of an IC engines.  I have been looking at radials for several years.  The animation on the home page was my first try.  Unfortunately the connecting rod hit in that one.  I need to see if the clearance is good. in this one.


The big part of the heads  10/10/2005

Over thanksgiving a new crank case was made, well several were made.  The next to last hole wandered and broke through the side so I will be making one more set.  Each set get easier to make and little design changes are getting added to solve the problems.  11/25/2005

Crank Case #3 is another dud.

See the broken drill at the 2 o'clock hole. 

The new larger holes for the back plate worked out well.  The connecting rods now hit the crank case so some relief was needed.  Then the rods on the bottom 4 cylinders hit the cylinder skirt.  A little tuning of the connecting rods helped but the sides of the cylinders needed a minor adjustment.  I checked the clearance drawings and they look good, parts seem to be to the drawings but this thing is so small and clearances even smaller.

Why do the photos look so bad and show all the defects.  The silver solder smear in the master rod looks innocent to the naked eye.

One more try will be needed. 




First fitting of cylinders. pistons and the full connecting rod assembly.  Broken taps, all the remade parts finally have paid off.  The pistons have a great fit, and it turns easily. A blast from a air hose causes it to move.  1/7/206

12/10/2006  It has been 11 months since I last worked on this engine.  I dropped it for the Simple Vertical when I could not electroplate the parts.  I was glad when I found all the parts.

The parts for one head.  The big item is the head, the small round finned items are the valve guides, and the rectangles are the valve boxes.


I made a new fixture to solder the parts together.

The original fixture was heated by a small torch and overheated the parts and caused  the parts to get tarnished.

The new fixture is heated with a 100 watt cartridge heater, I used a temperature sensor and controller but once the solder will melt on the fixture it is ready.


The 9 head assemblies.  A little clean up with a needle file and a light buff should have then ready.


12/17/2006  It is time to make al the little parts needed to flesh out the engine.  The brass parts are cam followers, the SS are push rods, and the copper is intake and exhaust ports. 


1/9/2007  Holidays are over and Cabin Fever is in a few days.  It is starting to look like a real engine.




Copyright 2005-2006,  Florida Association of Model Engineers and engine builder as noted above, All rights reserved.