The quality of the materials entering into the construction of a steam engine is an important matter. The principal factor in the construction of a steam engine is the cast iron. It is not alone sufficient that castings should be smooth and sound; it must be known that the important qualities of strength and duration are not lacking. A strong, hard mixture is best for cylinders, pistons, rings, valves, etc., while a softer mixture is more suitable for other parts which are not subject to wear.
The crank shaft, connecting rod, piston rod, crank pin and wrist pin are commonly forged from steel, the quality of which should be assured by a reputable maker and of a specified chemical analysis.
A good hard brass should be used for lining wearing surfaces, such as crank pin boxes, wrist pin boxes, etc.
The crank shaft bearings are generally lined with Babbitt metal, made after an approved formula.
Some makers prefer to use a good quality of iron in place of steel for the larger parts of the engine, such as crank shaft.
In the best shops cylinders are carefully tested for straightness and roundness by measuring with micrometer gauges reading to the one-thousandth part of an inch, eight diameters in each cylinder, four parallel to the shaft and four at right angles to it. Bushings for steam chests are turned six one-thousandths of an inch larger than the bore of the steam chest castings, which is the allowance we make for the forcing fit.
- New catechism of the steam engine 1902 page 49