Here are three spool valve engines. The one in the back is a direct implementation of mrpete’s single-acting spool valve engine using the excellent(!) drawings provided by toly@sysmatrix.net. If you ask for mrpete’s spool valve drawings, he will e-mail them to you.
The two in the foreground are also derived from the same source. Obviously, I liked the square head with eight head bolts better than the original round head. I also eliminated the spacer on the main shaft that positions the eccentric by doubling the thickness of the upright and machining the main bearing such that it is also a thrust bearing for both the flywheel and the eccentric. I like the thicker pedestal better, but that is subjective.
A simple video of a 5/8″ diameter A325 bolt tested in single shear. There are no boundary conditions confining the bolt and you can see early in the analysis that the bolt rotates freely about its long axis. Not shown are two large plates modeled in the analysis. The bolt stops spinning as these plates slide past each other, making contact with the bolt, and causing the shear deformation in the bolt.
This has been modeled in Abaqus Explicit 6.10.