The MSM "Big 4" are all 19mm bore/stroke slide valve engines. They are named after historical Australian Murray River paddle steamers and their ports. They are respectively:
Each of these basic models can be supplied with options for a low profile "Marine" flywheel, a traditional "Spoked" flywheel and also "Reversing" and "Non--reversing" configurations that have the classical Stevenson's reversing linkage design.
Unfortunately single cylinder engines do not reliable reverse, so only the Gem and Mildura are suitable for powering model boats in that they have full RC control abilities. Hence there is a special RC reversing option for these.
An early objective was to make a range of slide valve engines that shared component designs as much a possible. Thus there are only two crankshaft designs, one cylinder casting for all engines, one valve chest casting, one piston rod design, and the list goes on...! This has allowed more economic production runs with lost wax castings and subsequent maching of castings and the other components that are machined from stock.
The castings are made from a free machining brass alloy that is highly corrosion resistant. Non casting based components are either stainless steel or brass - again corrosion resistant and easy to maintain.