13. Drip feeds to cylinders and pistons. 14. Gear drive to pump. 15. Big-end nuts, lock-strip, and shims. 16. Gudgeon-pin lock. 17. Piston-ring retainer pegs. 18. Cylinder liner screwing into jacket. 19. Open-ended "can" admits air. 20. Fuel supply. 21. (Hot) side of water jacket makes surface carburetter. 22. Sparking plug (comprising positive electrode 23 and spark-producing make-and-break 24). 25. Lever attached to lever 26 via bearing 27 screwed into chamber neck 28. 26. Levers with mainspring 29 and inter-spring 30, and rocked by "cam" 31. 31. Cam with another alongside (for adjacent cylinder). 32. Positive busbar feed to all four cylinders. 33. Assembly retaining-rings. 34. Sealing disc. 35. Exhaust outlet ports. 36. Camshaft right along on underside of jacket and also driving oil pump 11 via 14. 37. Spring-loaded sliding pinion drives make-and-break shaft 38 through peg in inclined slot 39. 40. Cam to push pinion 37 along and so alter its angular relation with shaft 38 (to vary timing). 41. Exhaust-valve cams bear on rollers 42 mounted in end of rocker-arms 43. 44. Generator floating coils. 45. Friction-drive off flywheel. 46. Sight-feed lubricator (on stationary sleeve). 47. Hardwood chain tensioner.] The intake and exhaust valves were identical and of two-piece construction, with the stems screwed tightly into and through the heads and the protruding ends then peened over. This construction was not novel, having had much usage behind it, and it continued for a long time in both automobile and aircraft practice. One-piece cast and forged valves were available but here again it was a choice of the quick, cheap, and proven answer. The entire valve system, including guides and seats, was of cast iron, a favorite material of the Wrights, except for the valve stems, which were, at different times, of various carbon steels. Ordinary cold-rolled apparently was used in those of the original engine, but in later engines this was changed to a high-carbon steel.