These two were built by Dale Petty from Pasco, WA. The one on the right is the "conventional" Rider-Ericsson which has been around for several years EXCEPT, this one is a 3" model and is pretty new on the market. The one on the left is an "IMPROVED" Rider-Ericsson Hot Air Water Pumping Engine, and is also one of the 'newer' models available. Castings for these engines came from Myers Engine Works. http://www.myersengines.com/ >
Dale plans to build a 4" model (engine on right) from scratch (no castings available) which will give him the entire series from 1" to 6" bore. Dale is another excellent model builder.