Oh and a good site for info ... http://www.stirlingbuilder.com/troubleshooting-tips
As a complete aside you also have the opposite end of the scale with a Flame Licker Engine... where it intakes hot air from a flame source and then it cooling in the cylinder causes the piston to move UP due to the CONTRACTION of the cooling air ... I have thought about making a train with one I have , but its on the "to do" list which seems to get longer as I get older