The M122 is similar in many respects to the M101. The main differences are the twin cylinders and the shape of the boiler. The distinctively long and thin brass boiler is 7" long by 2" diameter. Like on the M101, the traditional single acting oscillating cylinders are totally enclosed by fixed brass covers which make them look much bigger (1" dia. x 2 1/4" long). The cylinders are actually 3/8" bore x 15/16" stroke (probably a nominal 1"). The pistons are lubricated by a pair of drip feed lubricators mounted over the ends of the cylinders. The cranks are large heavy brass disks which contribute significantly to the flywheel effect. Attached to the crank shaft is a small brass flywheel, 1 1/2" dia. x 7/16", and a small gear wheel, approx 5/16" dia. This engages a gear wheel 1 13/16" dia. on the second shaft.
The steam feed is taken from a small dome at the top of the boiler, internally, and the pipe exits through the side of the barrel, about half way down. It then goes via an in-line throttle to the cylinders. The exhaust pipes from the two cylinders terminate adjacently, after only a couple of inches. It looks as if they were originally fed to the bottom of the chimney, which is similar to the M101 but slightly shorter at 7".
The meths burner is a special Bowman design, similar to the M101 but shallower. The brass tank is 3" dia. by 7/8" high. Sticking out from this tank is a brass tube 4 3/4" long x 5/16" diameter, slotted along its length and containing the wick. When lit, the flame extends along the full length of the slot, which is almost the full length of the boiler.
The steel base plate is 9" by 11" and has a single row of Meccano standard holes, 3/16" dia. and 1/2" spacing, around all 4 edges.
As purchased, it was almost complete, apart from the missing exhaust pipe (which I remade from brass tube), and generally in reasonable condition. The boiler end at the chimney end was distorted (probably dropped at some time) and there was a slight leak around the chimney mounting screw. This was easily fixed with solder. The pistons were seized solid in the cylinders but freed after soaking in vinegar. The burner tube was slightly damaged. Rather than try to repair it, I just replaced the tube. After removal from the tube, the wick fell apart so I replaced it with string from a mop. The metal base was screwed to a hinged wooden base, presumably designed to take accessories. This was not original and not in good condition, so I have removed it. Otherwise, restoration consisted of cleaning, repainting and replacing washers.
The bottom photo on the left is in as acquired condition.