Husqvarna 122 HD60 Workshop Manual

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Contents

637Cylinder and pistonMedium to deep scores on the exhaust side.The piston ring is stuck in the groove.Black discoloration under the piston ringdue to blow-by.Exhaust side damaged by a broken pistonring. The piston ring parts damage the topsection and cause score marks.Cause:• Wrong type of two-stroke oil or petrol.• Incorrect oil mixture in the petrol.• Incorrect carburettor setting.Piston scoring caused by heavy carbon depositsToo heavy carbon depositing can cause damage similar to that caused by insufficientlubrication. However, the piston skirt has a darker colour caused by the hot combustiongases that are blown past the piston.This type of piston damage starts at the exhaust port where carbon deposits canbecome loose and get trapped between the piston and the cylinder wall.Typical for this type of piston damage is brown or black discoloration of the piston skirt.Piston damage caused by a too high engine speed.Typical damage from too high engine speed is ruptured piston ring/piston rings, brokencirclip on the gudgeon pin, faulty bearings or that the guide pin for the piston ring hasbecome loose.Piston ring breakageA too “lean” carburettor setting results in a too high speed and a high pistontemperature. If the piston temperature rises above the normal working temperature thepiston ring can seize in its groove, consequently it will not sit deep enough in its groove.The edges of the piston ring can then hit the top edge of the exhaust port and besmashed and also cause piston damage.A too high engine speed can also cause rapid wear to the piston ring and play in thepiston ring groove primarily in front of the exhaust port. The ring is weakened by thewear and can be caught in the port causing serious piston damage.Action:Change the fuel.Correct the carburettor settingChange to a fuel with the correct oil mixture.