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TKART magazine Tech Talk | Oil seals
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21 May 2017
The two-stroke models, which are almost always the types of engines used, have the task of sealing the crankcase, allowing them to function correctly and avoiding loss of fuel from the side holes in the crankcase for the insertion of the crankshaft
The oil seal is made of rubbery material whose characteristics may vary depending on the specific use (fluids that vary in terms of corrosion coming into contact with it, operating temperatures, etc.).
The elastomers present in the material may be silicone or nitrile rubber but, they are in any case sufficiently rigid and hard. Material deformity must be limited to allow longer durability but at the same time a minimum amount of elasticity must be maintained so that the oil seal fits the component on which it is mounted. Internally, there is a metal reinforcement ring in the rubber part.
The structure is circular in the outside, where the oil seal is in contact, in a static and forced manner, with at the height of the bench bearings, the crankshaft’s
housing, and so is its interior, where the sealing lips with a cushion profile rest on the surface of the crankshaft.
In a kart, the double sealing lip has a different interior, which is for sealing, and the exterior, which increases the duration of the oil seal by avoiding friction due to external particles entering between the oil seal and the crankshaft.
The sealing of the oil seal is in any case ensured by a helical spring in the interior that throttles the crankshaft.
For effective sealing (and a longer life-cycle), the surface of the crankshaft in contact with the oil seal should be thoroughly polished and be hard enough so that it does not wear out over time, considering the continuous rubbing, even if it is light, against the lips of the oil seal.
Oil seals close the area in which the crankshaft runs from the interior to the exterior of the crankcase
The oil seal in the engine
Oil seals are circular rubber elements with holes in the middle and with internal helical spring to optimise sealing
The 2-stroke engine for karts is an open system with a mixing inlet duct (suction PIPE) and a flue gas exhaust duct that starts from the exhaust socket and any lateral boosts. Clearly, because this system works properly, it is important that there are no other channels. However, the crankshaft is positioned in the crankcase, which exits both sides, connecting to the ignition rotor, on the one hand, and to the transmission gears or to the sprocket, on the other hand.
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