This engine runs fantastic, the problem is that the engine they sent does NOT match the item in the picture. I specifically wanted a thermoacoustic stirling engine with an "extended" hot tube. What they sent was the standard "short" hot tube variety. I already have 3 engines of this style, if I wanted another I could have purchased the one from this site for $23.99 or $19.99. Instead, I paid $29.99. This engine comes with bearings in the flywheel mount so it runs exceptionally fast. It is a great engine overall, but unfortunately not the engine in the sales pictures. Based of performance this engine is "5 star", however Sterlingkit should never substitute engines without customer authorization first