I originally found this engine on the cover of the Nov / Dec 2005 edition of The Home Shop Machinist. I hadn't really paid too much attention to it as I thought it was beyond my capabilities. I was also deep in other projects at that time. In February 2009 I started looking for a project; something just beyond the reach of my technical skills. Beyond, because it would challenge me and push me to learn and reach beyond my comfort zone.

It made sense to build from the bottom up. I wanted to build in the same order as assembly - I didn't want any parts on hand that couldn't be attached to another part. The Frame or as Terry calls it, the Tuning Fork was first.

Before I start cutting, I print the part off the Cad program and make sure that the size and location suits my mill and material. I also use it to zero the mill on the material.

Then let the fun begin...

The four extra holes on the left side are pin holes to align the Frame and the base.

Next came the pillow blocks. The basic dimensions are the same, sort of, but I did not split them but rather secured the bearings in place by way of a setscrew down below. Terry advised not to do this as it distorted the bearing enough to induce a bit of unwanted friction. But, once I installed these lovely (and rather expensive skate board bearings), along with the flywheel, a quick spin of the flywheel showed that it would spin for a very long time indeed.

The pillow blocks are also attached from below with button head cap screws.

As with all of the parts, they are only wet sanded to a moderate finish. Once everything is built and the engine running, I'll wet sand everything down to about 1000 grit and either leave raw or anodize & dye for a bit of colour.

They will be secured to the shaft with No. 4 set screws. Jeez those things are small.

These were eventually sent to the recycle bin. See new crank arms below.

You can see the same alignment holes in the base as in the frame above. They will also be added to the cylinder which joins the base to the frame.

It's starting to look a bit like the picture on the magazine cover.

A piece of MDF is next clamped to the mill and three matching .125" indexing holes are drilled. Then three .125" x .400" pins inserted. Now the part can be flipped over and laid on top of the MDF with the index pins exactly aligning with the holes in the part. You normally don't want to expose MDF to moisture but the work is all done in an hour or two and that's not enough time to adversely affect the MDF.

The second side is now milled and the part cut out. Note the nice finish on the 
edge this time from using an end mill of with the right length flute.

Everything is fitting just fine so far.

As it turned out, I left the hole the original size which was the same diameter as the cylinder ID whereas it needed to be the same diameter as the cylinder OD in order for it to slide over the cylinder. It gave me the opportunity to mount a mostly round part in a four jaw lathe chuck, center it using a dial test indicator, and opening the hole to the correct size. I knew theoretically how to do this but had never attempted it before. Remember what I said about pushing my limits above ???

You may not be able to tell but the fit of the retainer against the frame at the Four o'clock position leaves just enough room to slide a cigarette paper in there. As they say, sometimes it's better to be lucky than good.

I also like the more finished, less industrial look of button head cap screws in many places like on the cylinder retainer.

Notice the enlarged hole compared to the picture on the left.

This shows how the cylinder was cut leaving a shoulder on it
 to fit inside the retainer. The cylinder still need the diameter
 reduced to 1.375" to fit inside the recess of the body.

 Lapping will wait until the other cylinder to finished.

The retainer stands proud of the body a little too much at this point. 
What I had in mind was closer to about .050" or so - just enough so 
I was certain that the cylinder was firmly seated against the body. 
I may reduce the shoulder on the cylinder. But then again, maybe not;
 it actually doesn't look too bad as it is.

With such short screws there is no chance of distorting the cylinder. 

The cold end cylinder was the most time consuming. Grooving the exterior with the parting tool took the longest. Lots of tool chatter which, no matter what I tried, would not go away. I took this procedure extremely slowly so as not to end up with a lump of scrap after so many hours.

Hot end, cold end, and retainer completed except for holes.

Displacer piston connecting rod. That end mill is .020" and is just used for lettering and similar fine jobs.
The rod may end up being too heavy and have to be re-cut in aluminum. The bearings are router bearings from the local fine woodworking store.

The power piston was certainly one of the fussier parts to make so far. It needs to fit the cylinder extremely closely yet slide smoothly.

The Displacer Piston Barrel
 This is a very thin piece. The first one I made, I cut off a little long expecting to  face it off to exact length. It was too thin to hold tightly enough in the lathe chuck and when the cutting tool touched it, the end crumpled and ended up looking like a Cabbage Patch Doll.

The finished Displacer Piston.
Sometimes, I find that parts like the end caps can be made more accurately on the mill than the lathe. The thin .150" material is way too thin to grip effectively in the lathe chuck. I could have turned them from a thick rod but the parting off process may create its own issues. For me, at least, the mill was just as fast, more accurate, and required minimal touch up on completion.

I just couldn't quite get used to the crank arms I made previously. I saw one something like this on another engine and designed and cut these. So much better and in tune with the rest of the engine I think.

Finishing touches to follow