Ken, The square piston engine may be similar in operation to the Dake Square Piston engine. I am working on a steam powered fork lift truck that used a Dake engine and since I know your email addy, I can send you a photo of the innards of a Dake. I haven't started to build one yet because I need a few more photos of the lift truck and don't want to build an engine unless I can use it in the truck. The steam fork truck that I have photos for came from a glass factory, but they were also used in foundries. Look over the photo and see if the Robertson looks the same or similar to the Dake. Unka Jesse over the pond in Troy, TN fernj1@xxxxxxxxxxxxx From: "Ken Strauss" <ken.strauss@xxxxxxxxxxxx> Page 28 of "100 Great Models" shows a "Robertson Semi-Rotary Engine" which is described in "Modern Steam Engines" by Joshua Rose (page 329-330). Have plans for this engine for the modeller been published? MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.