Husqvarna 243RJ Workshop Manual

Also see for 243RJ: Operator's manual

645Cylinder and pistonExhaust side damaged by a broken pistonring. The piston ring parts damage the topsection and cause score marks.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 piston tempera-ture. If the piston temperature rises above the normal working temperature the pistonring can seize in its groove, consequently it will not sit deep enough in its groove. Theedges of the piston ring can then hit the top edge of the exhaust port and be smashedand also cause piston damage.A too high engine speed can also cause rapid wear to the piston ring and play in the pis-ton ring groove primarily in front of the exhaust port. The ring is weakened by the wearand can be caught in the port causing serious piston damage.The guide pin for the piston ring has beenpushed up through the top of piston.Irregular grooves on the piston’s inlet sidecaused by a broken roller retainer.Deep, irregular grooves caused by a loosecirclip. Shown here on the piston’s inlet side.Piston ring guide pinvibrated looseA too high engine speed can cause theends of the piston ring to hammer againstthe guide pin when the piston ring movesin its groove. The intensive hammeringcan drive out the pin through the top of thepiston causing serious damage also to thecylinder.Damage caused bygudgeon pin circlipsA too high engine speed can causethe gudgeon pin circlips to vibrate. Thecirclips are drawn out of their grooves dueto the vibrations, which in turn reducesthe circlips’ tensioning power. The ringscan then become loose and damage thepiston.Bearing failureFailure of the crankshaft bearing or onthe connecting rod bearing is usuallycaused by a too high engine speed,resulting in the bearing being overloadedor overheating. This in turn can cause thebearing rollers or ball to glide instead ofrotate, which can cause the roller or ballretainer to break.The broken debris can be trappedbetween the piston and cylinder wall,damaging the piston skirt.Debris can also pass up through thecylinder’s transfer channels and causedamage to the top and sides of the pistonas well as to the cylinder’s combustionchamber.