The shoulder bolt / pin / hollow centre drum setup is very elegant! Like it! great progress Chris.

This is coming on very well.

On using the face mill for refinishing the cylinder and mouth piece bolting faces, the surface you have there looks fine for purpose, but when you want a better finish for functional or cosmetic reasons, a fly-cutter will generally do that, especially with a radius at the tool tip, and a sweep radius sufficient to cover the whole surface in one pass.

While I am sure your spool valve will work fine, I would suggest for next time, the sharp working edges should be just broken with a fine stone rather than being chamfered or rounded. This would be more important with a piston-valve engine, where anything but a sharp edge would adversely affect the timing.

Ah right, got it thanks - I like to understand how they work rather than blindly make these things!

Thanks guys!  Getting close to having it spinning (by hand anyway). This afternoon I cut the pivot pins for the lower ends of the arms

and turned/threaded the shoulder bolts for the upper ends of the upper arms:

Then thread into the widest yoke, and is a slip fit on the inner yoke and the fitting on the center spindle. Here they are assembled to show how the pins project through the inner yoke:

Here they are assembled onto the spindle:

and the parts so far. Next I'll make up the flyballs to get things spinning. The balls will have a pivot rod through them to engage withg the yokes, and a hole down from the top to go onto the ends of the upper rods.

Yeah, the exhaust goes out the ends of the valve tube.