I am in progress of designing a model radial engine for small model airplanes. Not based on any real engine, more of an impression. Crankcase is the next step. The examples in the photo are 2cm high. The file is much larger so you can size them to your own needs in the slicer.
Still a bit rough, but good enough for messing around with.
Just glue the halves together.
Done on 123Design. It has helped me in learning the software.