On a nitro RC car engine, the clutch bell gap is the amount of play (gap) between the clutch bell and the flywheel, as shown in the diagram. There should be a gap there that allows the clutch to operate normally, so it doesn't hang up on the flywheel. The gap should not be too large, or it will prevent the clutch shoes from engaging fully, so the shoes will wear unevenly. Your RC car's manual will usually suggest a good distance for this gap.
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