While it’s true that many production motorcycles have over the years lubricated their gears by “splash” (that is, by filling the gearbox with oil up to the shaft centerlines or thereabouts), this method has drawbacks. The biggest is power loss through oil churning. Everyone who ran one of Yamaha’s TZ250/350 twins between 1972 and 1980 used the technique of running the full 1.4 quarts for first practice if the engine had been apart, then draining the gear oil and refilling with just a quart. Kawasaki’s KR250 twin, when first run in 1975, generated so much heat in its gear oil that it burned the paint off its gear case. The special problem of the KR was that it was designed for racing and therefore had no extra volume in its gear case to accommodate a kick-start mechanism. Further, that engine’s two cranks were geared together by a pair of roughly 4-inch-diameter gears whose teeth engaged at 200 feet per second, and they were lubed just as was the transmission: by sawing into standing oil. Original fill was 1,100cc but the factory soon advised operators to reduce this to 600cc. I made a trough of sheet metal to keep the trans oil off those high-speed gears, with just a .040 hundredths hole to let in adequate oil. In effect, this same scheme was used on many primary gears. When the engine started, oil level was equal to that in the gearbox, but the fast-moving primary wheel soon threw that oil “over the wall” into the main gearbox. Some was caught in small collectors whose purpose was to direct oil into the centers of the gearshifts, from which radial drillings would lubricate the free-spinning gears. Oil re-entered the primary case through holes of limited area at the bottom. This system prevented excess heat generation and power loss by limiting the volume of oil reaching the primary gears. The KR250 had no such system for its high-speed gears. The trough I made for them saved enough power that rider Ron Pierce was able to put the bike on pole for the 1976 Daytona 250 race, but unrelated problems made him a DNF. Yamaha engineer Noriyuke Hata, hired to build a 125cc GP bike in 1961, created a much better system. Transmission gears were placed far above the gear oil level and were lubricated by oil jets from an overhead drilling, supplied by a small lube pump. Subsequent race bikes not based on production crankcases employed this system, common examples being the Yamaha TZ750 and TZ250H and subsequent. A similar system was used on Suzuki’s 500 GP engines in the 1990s, revealed by the visible transverse “bump” across the top of the gearbox, with six plugged-and-epoxied vertical holes. For the highest mesh speeds, lube oil cannot be delivered on the closing side of the mesh as it was on the above race bike gear sets, for oil trapping could occur, producing destructive wedging stress and vibrations. In such cases, the oil is delivered either on the opening side or against the inside of the rim of the gear. In the latter case, this oil is mainly a coolant, and lubrication occurs via the mist that fills a high-speed gear case. If you spend time in airports, you have seen Pratt & Whitney’s large-graphic ads for the upcoming GTF, or Geared TurboFan engines. An illustration (see main photo above) shows the 3:1 planetary gear reducer with five planet pinions, provided to allow the low-pressure compressor to operate at its best speed without requiring the fan to suffer losses by having to operate at highly supersonic tip speeds. Estimates of these speeds are 10,500 rpm for the LP compressor and 3,500 rpm for the fan (at take-off). If this gear set transmits 15,000 horsepower to the fan and is 99 percent efficient, that leaves 150 hp (the heat equivalent of 150 operating kitchen toasters) to somehow be removed by the lube oil. I want to know how they avoid the obvious problems of oil trapping, tooth surface overheating, and mechanical loss! As you can see, I love gears.Gadget Reviews: mamaktalk.com
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