Didactic model, horizontal gas engine, wood/steel, made by Cussons Ltd, Manchester, UK, 1890-1920. This hand-operated sectioned model shows the essential features of a four-stroke gas engine. On the out-stroke of the piston, gas and air are drawn into the cylinder through the two poppet valves actuated from levers situated under the cylinder. The gas main connection and the air intake are indicated on the model. On the return stroke the gas-air mixture is compressed, its temperature rises and it is ignited by the firing tube which is heated by a Bunsen burner. On the second in-stroke of the piston the products of combustion are exhausted through the exhaust poppet valve. The engine is prevented from overheating by the water space surrounding the cylinder; the cooling water inlet and outlet are marked.
The piston pin connects the piston with the connecting rod which, in turn, is connected to the crank pin and then the crankshaft. The 'big end' of the connecting rod is sectioned to show the big end bearing and the bolted means of attachment. An arrow shows the direction of rotation of the crankshaft. The piston moves between two positions: the inner dead centre position is indicated by the shaded line separating the clearance space from the remainder of the cylinder volume; and the outer dead centre position occurs when the right hand end of the piston protrudes beyond the end of the cylinder. The model indicates that the ratio of 'clearance volume' to 'stroke volume' is about 50%, which was typical of gas engines built in the late nineteenth century. Running along the back of the model, and driven from the crankshaft at half engine speed, is a camshaft that actuates the inlet and exhaust valves.
Different parts of the model are painted grey, blue, orange and black. Part names and arrows are added in white paint. Sectioned parts have white hatching added in accordance with conventional engineering drawing practice.
Noel Svensson, 'Object documentation report, object number B1741' (unpublished).
In addition to part names and arrows, the model bears the maker's name: 'Cussons Ltd, The Technical Works, Manchester, England'.
It is also marked 'No 510'. This is probably a University of Sydney stock number.