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Use this guide to replace the piston assembly in your Echo Chain Saw CS-4910 (2020).
Although it's not necessary to remove the guide bar, it's highly recommended you do so to minimize any damage to the chain and to yourself.
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Make sure you have the ignition switch turned off before starting your repair.
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Use your fingers to loosen the air filter cover knob.
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Remove the air filter cover.
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Remove the air filter
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Use your fingers to pull up and disconnect the spark plug boot.
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Use a 13 mm wrench to loosen and remove the two nuts securing the sprocket guard.
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Pull the sprocket guard straight off its two pegs and remove it.
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Pull the saw chain away from the tip of the guide bar to unclip it.
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Push the guide bar towards the back of the device to unclip the rest of the saw chain.
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Pull the guide bar away from the device to separate the saw chain from the clutch drum.
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Remove the guide bar and the saw chain.
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Use a flathead screwdriver, or a 3 mm hex key, to remove the three 18 mm screws securing the engine cover.
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Pull the engine cover straight up off the engine.
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Remove the engine cover.
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Use your fingers to pull the top-most fuel pipe out of the carburetor.
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Lift the choke rod out of its recess in the chassis.
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Twist the rod counter-clockwise to disconnect it from the carburetor.
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Remove the choke rod.
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Remove the four screws securing the carburetor and the air filter adapter:
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Use a 3 mm hex key to remove the two 20 mm-long screws.
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Use a 4 mm hex key to remove the two 53 mm-long screws.
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Pull the air filter adapter straight off the carburetor and remove it.
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With the carburetor's choke valve facing you, tilt the carburetor up and to the left to expose the right-most fuel pipe.
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Use your fingers to disconnect the right-most fuel pipe.
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Lift the carburetor straight off the throttle rod and remove it.
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Remove the five screws securing the handle:
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Use a 4 mm hex key to remove the four 24 mm-long screws (on the side and bottom).
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Use a 3 mm hex key to remove the 18 mm-long screw.
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Pull the handle towards the rear of the device to remove it.
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Use a 3 mm hex key to remove the two 20 mm-long screws securing the intake insulator.
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Use a pick tool to remove the insulator intake collar.
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Use a flathead screwdriver to fold the lip of the intake bellows inside the intake insulator.
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Lift the intake insulator out of its recess and remove it.
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Slide the bellows holder off the intake bellows and remove it.
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Insert a flathead screwdriver between the intake bellows and the cylinder head.
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Pry with the screwdriver to separate the intake bellows from the cylinder head.
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Remove the intake bellows.
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Use a spark plug socket wrench to loosen the spark plug.
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Pull the spark plug straight out of the cylinder head and remove it.
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Use a 9/16 inch wrench to loosen the decompression valve assembly.
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Pull the decompression valve assembly straight out of the cylinder head and remove it.
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Use a 4 mm hex key to remove the two 23 mm-long screws securing the muffler.
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Use a 3 mm hex key to remove the 10 mm-long screw securing the muffler plate.
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Use a 4 mm hex key to remove the two 23 mm-long screws securing the muffler.
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Pull the muffler straight out of its recess and remove it.
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Use a 4 mm hex key to remove the four 25 mm-long screws securing the cylinder head.
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Lift the cylinder head away from the chassis to expose the piston.
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Remove the cylinder head.
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Make sure the two black piston rings are aligned in their grooves so the piston can compress properly in the cylinder head.
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Apply two-stroke oil to the piston head and the cylinder walls before reinserting the piston.
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Use snap ring pliers, or a flathead screwdriver, to remove one of the piston snap rings.
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Repeat this procedure for the snap ring on the opposite side of the piston.
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Flip the chain saw on its side so the clutch drum is facing upward.
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Grip the bottom of the piston.
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Use a hammer and a pin punch to tap the piston pin through its recess.
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Remove the piston pin.
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Pull the piston off of the piston rod to disconnect it from the crankshaft.
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Remove the piston, its needle bearing, and the two washers.
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Use a pair of pliers to remove the cylinder head gasket from the crankcase.
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To reassemble your device, follow these instructions in reverse order.
To reassemble your device, follow these instructions in reverse order.
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