Algodoo

They're not very good. You should use boxes instead of polygons for the pistons (if you want, use a transparent box behind the piston) because boxes have better collision. Also the flywheel should be a circle so that it doesn't swing, and the timing slips after some time. Use springs or use bend instead of a brake on the timing axle. If you make the pistons' travel (bore-stroke ratio) a lot less you'll have a faster engine, and maybe it's stronger too.

Thanks for comment!