solidworks stirling hot air engine (Subdivision ready 3D model) is available on CGTrader for $5. Original author: lets-make-it-cad.
SLDPRT (SolidWorks, filesize: 6.56 MB), AMF (amf, filesize: 43.9 MB), AD_PRT (Alibre/Geomagic, filesize: 3.56 MB), IGE (IGES, filesize: 20.9 MB), STP (STEP, filesize: 17.6 MB)