During WW I, exhaust valves, connecting rod big end bearings and spark plugs gave the most trouble. In cylinder construction three difficulties presented themselves: (a) the valves warped and burned, (b) the valve seats did not remain true and (c) in long runs the valves hammered into the seats so that the tappet clearance was lost and the valves were held open. The present type of Wright cylinder as shown at Fig. 165 D and the use of tulip head silchrome steel valves have greatly reduced valve troubles. Refinement of details of the 1,947 cubic inches 60 degree V-type 12-cylinder Wright T-3 engine has enabled it to be used satisfactorily at speeds greater than 2,200 r.p.m. and to develop 750 horsepower with approximately 140 pounds mean-effective pressure at 20 per cent less weight per horsepower than that of the original engine.

The Wright E2 engine, shown at Fig. 1 is no longer in production but it was a popular type for some years. This engine has practically all of the characteristics of the Hispano-Suiza as previously described. The improved and refined Wright E4 shown at Figs. 2, 3 and 4 is the type that has been operated for 310 hours with one cylinder assembly, or long enough to have driven an airplane 31,000 miles without overhauling. After a new set of cylinders had been fitted, the other parts were run an additional amount so that the equivalent of 57,200 miles operation was obtained with only minor external adjustments. The old Model A engines developed a maximum of 175 horsepower at 1,800 r.p.m. whereas the latest models of the same type develops a maximum of 285 horsepower at 2,300 r.p.m. The bore of the E4 cylinders is 4,710 inches, the stroke is 5,110 inches and the total displacement is 718 cubic inches. This engine is no longer in production, all demands for this horsepower being supplied with radial air-cooled engines.