This interesting marine engine is of unidentified make, probably scratch built. I don't normally collect scratch built engines but this one is rather interesting. There was also a possibility, at the time of purchase, that it could be identified as some 19th century maker, but this is now unlikely.
The engine is interesting in that it is built into a frame shaped to fit into the shape of a boat hull. It is an open lattice style frame so that the cylinders and crankshaft are clearly visible.
The two cylinders are in a V formation set at 90 degrees and connected to a single crank. They are double acting oscillating cylinders with the ports built into the pivot bearing, similar to full sized oscillating cylinders. The bore is 5/8" and stroke 15/16" (probably a nominal 1").
As acquired, there were a few problems. Two out of the three head retaining screws were missing from one of the cylinders. I have replaced all three so that they match. The steam feed pipes were originally soldered onto the port blocks with obviously too little heat (probably with a soldering iron). These had been cut off leaving only unusable stubs. I have fitted new pipes with a T junction. I have left the exhaust ports open to the atmosphere. The big end bearings are extremely loose. Due to the design of the crankshaft, it will not be easy to fit sleeves. The brass frame is distorted at one point but it doesn't appear to affect operation. I will probably leave well alone for fear of cracking the cast brass frame if I attempt to straighten it.