31. The distinction between a worm and a helical gear is that at least one tooth persists for a full rotation around the helix. 32. The gearbox was a four-speed and reverse constant-mesh unit, with helical gear trains for second and third gear. 33. Their advantage over the helical gears is that the side-thrust of one half is balanced by that of the other half. 34. The engine has a 2.7 : 1 Propeller Speed Reduction Unit ( PSRU ) with helical gears in an oil bath. 35. In a stable orientation, the helical gear faces are oriented so that each axial force is directed toward the center of the gear. 36. If the gear in a worm-and-gear set is an ordinary helical gear only a single point of contact is achieved. 37. In a helical gear , however, a plane can be normal to only one tooth at a point lying in the plane surface. 38. A helical gear pressed in No . 3 counterweight drives twin contra-rotating balance shafts in the shaft housing within the lower crankcase. 39. If a helical gear is being roughed out, then the table rotates and moves along the vertical axis to interpolate the helical path. 40. The two propellers are powered by two meshing and counter-rotating shafts, powered by helical gear wheels running in an oil bath.
