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10 Here’s a shot of the input shaft and the main gear after it has been pulled from the case. Note the groove cut into the face of the gear and the hole in the shaft that’s on the same spline the groove in the gear runs to. The purpose of this hole is to feed oil to the needle bearings the shaft spins on. (The needle bearings have been removed, but you can see the housing bore it spins in.) When reinstalling the gear onto the input shaft, you must make sure the groove in the gear and the hole in the shaft line up, otherwise, Cook says the needle bearings will be burnt up by your second or third night of racing.