Legend For Figure 3a1

15. Idler gear

16. Idler gear spacer

17. Hydraulic lifter

18. Intermediate gear spacer

19. Intermediate gear

20. Tappet and roller assembly

21. Pinion gear

22. Cam gear

23. Breather gear

24. Breather screen

25. Chain oiler adjustment screw

26. By-pass valve

27. Oil feed pump drive gears

28. Oil scavenger drive gears

29. Oil return nipple

30. Oil pump

31. Oil feed nipple

32. Check valve

33. Crankcase

34. Flywheel

35. Crankpin

36. Connecting rod roller bearing

37. Tappet guide

38. Connecting rod

39. Tappet adjustment

40. Piston

41. Cylinder

42. Exhaust valve

43. Exhaust valve guide

44. Valve spring

45. Rocker arm bearing inder connecting rod is forked to fit around the single-end front cylinder connecting rod, allowing a single connecting rod-crankpin connection to the flywheel.

Flywheel rotation is clockwise (viewing engine from right side). Using the front cylinder firing position as a starting point, the rear cylinder fires at 315 degrees rotation (360 degrees minus the 45 degrees between cylinders). The front fires in an additional 405 degrees (360 degrees plus the 45 degrees between cylinders), completing the 720 degrees of flywheel rotation necessary for the four piston strokes.

The gearcase is located on the right side of the crankcase and houses a gear train which operates and times the valves, ignition and crankcase breather. The generator is also driven from the gear train. The rotary crankcase breather valve is located between crankcase and gearcase compartments and functions to relieve crankcase pressure caused by downstroke of pistons, and controls the flow of oil in the lubrication system.

A single cam shaft with four cam lobes is gear driven. The engine valves are opened and closed through the mechanical linkage of tappets, push rods and rocker arms. Tappets serve to transmit the cam action to the valve linkage. Hydraulic lifters installed in the tappets automatically compensate for heat expansion to maintain a no-lash fit of parts. Valve and breather timing are obtained by meshing gearcase gears with timing marks aligned.

Ignition spark is produced by operation of circuit breaker, ignition coil and spark plugs. The breaking of a single set of breaker points by a double-lobe cam on the timer shaft determines the spark timing. The narrow lobe times the front cylinder. The wide lobe times the rear cylinder. Both spark plugs fire on each breaker point opening (twice per complete cycle of 720 degrees flywheel rotation since cam shaft operates at 1/2 engine speed). The valves are timed to produce combustion conditions in only one cylinder at a time so the spark in the other cylinder occurs ineffectually during its exhaust stroke.

Most other engine components function similar to usual internal combustion engine design. For further description of part function, see pertinent manual sections.

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