cylinder numbering

In aircraft reciprocating engines, except rotary engines, the propeller shaft end of the engine is always the front end, and the accessory end is the rear end, irrespective of how the engine is mounted. An engine is referred to as right or left rotation, as viewed from the rear, or accessory, end. Radial engines are numbered clockwise, as viewed from the accessory end. In V-engines, the cylinders, or cylinder banks, are known as the right bank and the left bank, as viewed from the accessory end. The numbering of engine cylinders is shown in the diagram. The numbering of the cylinders of the opposed engine begins with the right rear as 1 and the left rear as 2. The cylinder forward of 1 is 3; the one forward of 2 is 4; and so on. The numbering of opposed engines is not standardized, but one arrangement is shown in the illustration. Single-row radial engine cylinders are numbered clockwise when viewed from the rear end. Cylinder 1 is the top cylinder. In the double-row engines, the same system is followed. The number 2 cylinder is the top one in the rear row. The number 2 cylinder is the first cylinder clockwise from 1, but 2 is in the front row. The next clockwise cylinder is 3, but it is in the rear row. Thus, all even-numbered cylinders are in the front row. This is the normal standard method of numbering engine cylinders, but some manufacturers do follow a different pattern.