Thursday, June 27, 2019

Webster Update #2

Most of the shop time in the last couple of weeks was spent on the cylinder. The prints say "12L14 Steel or Cast Iron". I ended up buying 1018 Cold Rolled Steel on my shopping session, so that's what it's made out of.   (Not included in the two weeks was time spent on the side project, drilling out the brass bushing and so on - or other little things going on)

In this photo, you'll note four (#4-40) screws that fasten the frame to the cylinder.  I spent some time trying to figure out how to locate the holes for those screw holes, given the tools I have, and eventually decided to chuck up the cylinder on my Sherline rotary table and drill the four holes as a bolt circle. I did the tapping using my drill press as a vertical guide and then spotted and drilled the other two holes on the drill press.

Overall view with the cylinder and frame resting on the Sherline/A2ZCNC mill.  That large hole on the right is for the spark plug.  The three holes on the side facing the camera, below the centerline of the cylinder, are for the intake and exhaust valves, made as a separate subassembly. 

The cylinder isn't "Done done"; it's about .010" short of the .873 recommended in the drawings. I managed to break my telescopic gauge for measuring the Internal Diameter and am awaiting the replacement. I still have to make the piston and lap that to the match the cylinder.  Both piston and cylinder are intended to end up 0.875", but with them being custom fit to each other rather than interchangeable parts, they could really be any size.  For small, one at a time engines like this, it's pretty common to custom fit the piston to the cylinder.  While a lot of guys make cast iron piston rings in various ways, there are hi temperature polymer rings (Viton is the brand) that work well.  The design doesn't call for any kind of piston rings.


  1. How are you planning to lap the cylinder and piston together? Use something like valve grinding paste? I've got some extremely fine Cerium Oxide I use for polishing water spots and other stuff off auto glass. You might not need anything that fine, but it's an option.

    1. Yeah, it's grinding paste. The tooled finish is supposed to be good enough that I can start with 400, then 600. I should get something like 320 in case it's not as smooth as it should be, as well as 400 and 600.

  2. From my industrial life, I note that Loctite Corp has absorbed the entire line of Clover grinding and lapping compounds, down to 3 micron grain size. It might be interesting or useful to research how the model airplane engine industry made such fine piston/cylinder fitting.

  3. This beats the hell out of making whirlygigs. (TM)