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  How to Replace the Piston & Rod Assembly on a Ryobi Trimmer

Why Read This Article?

Finish Nailer Repair - Replacing the Driver Guide (Ridgid Part # 79004001022)

Article Breakdown

Finish Nailer Repair - Replacing the Driver Guide (Ridgid Part # 79004001022)

Video

Tools & Materials

Fix Factor: Moderate Duration: About 1 hour Frequency: As necessary Tools Required: Receptacle for draining fuel, Phillip's screwdriver, ratchet and socket set, Torx wrenches, starter rope (or similar object), spark plug wrench or socket, adjustable pliers, long-nosed pliers, rubber mallet, standard screwdriver, 2-cycle oil, razor blade Part #: 753-04367

How to Replace the Piston & Rod Assembly on a Ryobi Trimmer

Finish Nailer Repair - Replacing the Driver Guide (Ridgid Part # 79004001022)
Replacing the piston on a Ryobi trimmer The Facts

String trimmer out of whack? It's time to face the fix. Whether you are a legendary landscaper or a weekend weed whacker, eReplacementParts.com provides the parts, procedures and facts you need to fearlessly fix what fails you.

The piston is a central component of your trimmer's two-cycle engine. It both provides compression within the engine, as well as transfers the energy from combustion to the crankshaft (which creates rotation).

The piston and rod assembly consists of the piston itself, the rings, the connecting rod, and the connecting rod bearing. The most common reason for replacing the piston assembly is worn or damaged piston rings.

Damage to the piston rings can occur several ways:

Lack of oil will allow the rings to contact the cylinder, causing scoring, and eventually, seizure of the engine. Dirt in the cylinder will act like sandpaper, quickly wearing away the piston rings. Using old or stale fuel will cause varnish build-up, which will eventually 'glue' the rings to the piston. Because the rings seal against the cylinder, any of these conditions will often damage the cylinder. As such, whenever you are investigating with a piston ring problem, you should also carefully inspect the cylinder for damage.

Replacing the piston assembly is not the simplest repair, but it is definitely something you can do yourself; especially when you follow these instructions. This article provides step-by-step instructions for replacing the piston and rod assembly on a Ryobi string trimmer.

Let's get started.

The Fix   REMOVING THE PISTON [top] 1. Remove the rear cover.

Remove the (4) screws from the rear cover.

 Remove the rear cover screws

 

 

Remove the rear cover from the engine.

 Remove the rear cover

 

 

  2. Remove the carburetor.

Drain any excess fuel from the fuel tank prior to servicing the carburetor or the fuel lines.

 Drain the fuel before servicing

 

 

Remove the (2) screws from the carburetor assembly.

 Remove the screws

 

 

Remove the choke plate and choke assembly from the carburetor.

 Remove the choke assembly

 

 

Disconnect the throttle cable from the carburetor (this is accomplished using a lift-and-twist motion).

 Remove the throttle cable

 

 

Remove the (2) fuel lines from the carburetor. These lines should pull away from the carburetor inlets relatively easily (by hand); however, small pliers may be used as necessary to disconnect the fuel lines from the carburetor.

 Remove the fuel lines

 

 

Remove the carburetor from the engine.

 Remove the carburetor

 

 

  3. Remove the muffler.

Remove the (2) screws from the muffler assembly.

 Remove the screws

 

 

Remove the muffler and exhaust gasket from the engine.

 Remove the muffler

 

 

  4. Remove the carburetor mounting assembly.

Remove the (4) screws from the carburetor mounting assembly.

 Remove the screws

 

 

Slide the end of the throttle cable through the opening in the carburetor mounting plate.

 Remove the cable

 

 

Remove the carburetor mounting plate from the trimmer (this assembly includes the fuel lines and the fuel tank).

 Remove the carb plate

 

 

  5. Disconnect the clutch housing and shaft from the engine.

Remove the (4) screws from the clutch housing.

 Remove the screws

 

 

Remove the clutch housing and shaft from the engine. (The throttle cable should also slide freely from the opening in the engine housing.)

 Remove the clutch housing

 

 

  6. Bind the engine.

This step effectively binds the engine, which facilitates the removal of key components (described in subsequent steps).

 Bind the engine

 

 

Disconnect the spark plug boot from the spark plug.

 Pull the plug boot

 

 

Use a spark plug wrench (or socket) to loosen the spark plug.

 Loosen the spark plug

 

 

Remove the spark plug from the engine.

 Remove the spark plug

 

 

Insert the end of an old starter rope (or similar rope) into the engine cylinder (through the spark plug hole). Continue feeding the rope into the cylinder until the piston is unable to move.

 Insert a rope into the cylinder

 

 

  7. Remove the clutch drum.

Loosen the internal screw on the clutch drum using a Phillip's screwdriver (loosen the screw until the clutch drum disengages the spindle; it is not usually necessary to remove the screw entirely).

 Loosen the drum

 

 

Remove the clutch drum from the spindle.

 Remove the drum

 

 

  8. Remove the clutch assembly.

Cover the clutch assembly with a shop rag to prevent damage during removal.

 Cover the clutch with a rag

 

 

Use adjustable pliers to loosen the clutch assembly.

 Loosen the clutch

 

 

Remove the clutch assembly from the spindle.

 Remove the clutch

 

 

  9. Remove the starter assembly.

Remove the (5) screws from the starter assembly. Four of the screws secure the starter to the engine; one screw secures the plastic base.

 Remove the screws

 

 

Gently lift the starter assembly away from the engine. (At this point, the assembly will remain tethered to the engine via the primary ignition wire.)

 Lift the starter away

 

 

Use long-nosed pliers to disconnect the ignition wire from the ignition.

 Remove the ignition wire

 

 

Remove the starter assembly from the engine.

 Remove the starter

 

 

  10. Remove the flywheel.

Remove the flywheel spacer from the crankshaft.

 Remove the spacer

 

 

Grasp the flywheel and raise the entire engine assembly slightly above the work surface.

 Lift the engine by the flywheel

 

 

Continue holding the flywheel securely with one hand, while striking the end of the crankshaft with a rubber mallet. Repeat this step until the flywheel disengages the crankshaft and engine.

 Strike the end of the shaft

 

 

Remove the flywheel assembly from the engine.

 Remove the flywheel

 

 

Use a pick or small screwdriver to gently pry the woodruff key from the base of the crankshaft.

 Pry the woodruff key

 

 

Remove the woodruff key from the crankshaft.

 Remove the woodruff key

 

 

  11. Remove the piston assembly.

Remove the (2) screws from the crankcase assembly.

 Remove the screws

 

 

Carefully separate the cylinder from the crankcase assembly (the piston should slide freely out of the cylinder).

 Separate the halves

 

 

Remove the piston from the crankcase assembly by sliding the connecting rod (and bearing) off of the crankshaft.

 Disconnect the piston rod

 

 

  12. Remove the cylinder gasket.

Remove the cylinder gasket from the cylinder assembly.

 Remove the gasket

 

 

Use a razor blade to scrape away any remaining gasket residue.

 Scrape the old gasket away

 

 

  13. Install the cylinder gasket.

Install the cylinder gasket onto the cylinder assembly.

 Install the new gasket

 

 

  INSTALLING THE NEW PISTON [top] 14. Install the piston assembly.

Lubricate the inside of the cylinder and the outside of the new piston assembly with two-cycle engine oil.

 Lubricate the piston assembly

 

 

Align the gaps of the piston rings with the roll pins in the grooves. (The roll pins should be centered between each of the gaps.)

 Align the gaps

 

 

Compress the piston rings (ensure that the gaps remain aligned with the roll pins).

 Compress the piston rings

 

 

ORIENTATION IS CRITICAL FOR PROPER FUNCTIONALITY OF THE PISTON. Note that one side of the piston skirt has been cut-away in a circular shape. This "cut-away" section of the piston skirt should face the ignition coil.

 Orient the piston correctly

 

 

The reverse side of the skirt is straight. Do not install the piston with the straight portion of the skirt facing the ignition coil.

 Orient the piston correctly

 

 

Continue to hold the piston rings in compression, and carefully slide the piston into the cylinder; ensure that the piston rings slide smoothly into the cylinder. (Do not force the piston into the cylinder).

 Install the piston

 

 

  REASSEMBLING THE UNIT [top] 15. Connect the crankcase to the cylinder.

Connect the piston (connecting rod bearing) to the crankshaft.

 Connect the piston rod

 

 

Connect the cylinder to the crankcase.

 Connect the two halves of the engine

 

 

Secure the crankcase to the cylinder with the (2) screws.

 Secure the engine case

 

 

  16. Reinstall the flywheel.

Install the woodruff key into the slot on the crankshaft.

 Install the woodruff key

 

 

Tap the woodruff key lightly to seat it into place.

 Tap the key into position

 

 

Install the flywheel onto the crankshaft spindle, ensuring alignment of the keyway with the woodruff key.

 Install the flywheel

 

 

Use a rubber mallet to tap lightly around the surface of the flywheel (not the spindle). It is not necessary to completely secure the flywheel with the mallet; just tap it enough to ensure that the internal components engage and seat properly. Installation of the clutch assembly (in subsequent steps) will secure the flywheel to the crankshaft.

 Tap the flywheel lightly

 

 

  17. Reinstall the starter assembly.

Slide the spacer onto the crankshaft.

 Install the spacer

 

 

Connect the ignition wire to the ignition coil.

 Connect the ignition wire

 

 

Install the starter assembly onto the crankshaft; tuck the ignition wires into the channel on the starter housing as you perform this step.

 Install the starter and tuck the wires

 

 

Align the starter assembly with the mounting holes on the engine.

 Align the holes

 

 

Hold the starter assembly in place while pulling gently on the starter rope. This will engage the starter pawls and ensure proper alignment.

 Pull the rope gently to engage the starter

 

 

Secure the starter assembly to the engine with the (4) screws.

 Secure the starter

 

 

Install the plastic base.

 Install the base

 

 

Secure the plastic base with the (1) screw.

 Secure the base

 

 

  18. Bind the engine. (Again.)

Insert either end of an old starter rope (or similar rope) into the engine cylinder (through the spark plug hole). Continue feeding the rope into the cylinder until the piston is unable to move.

 Bind the engine

 

 

  19. Reinstall the clutch.

Install the clutch washer.

Install the washer

 

 

Thread the clutch onto the spindle until it is hand-tight.

 Install the clutch

 

 

Place a shop rag over the clutch assembly to prevent damage during installation.

 Cover the clutch with a rag

 

 

Use adjustable pliers to secure the clutch to the engine.

 Secure the clutch with pliers

 

 

  20. Reinstall the clutch drum.

Install the small spacer washer onto the spindle.

 Install the washer

 

 

Install the clutch drum onto the clutch.

 Install the clutch drum

 

 

Secure the clutch drum to the spindle with the internal screw.

 Secure the clutch drum

 

 

  21. Reinstall the spark plug.

Remove the binding (starter rope) from the cylinder.

 Remove the rope from the cylinder

 

 

Install the spark plug into the cylinder.

 Install the spark plug

 

 

Use a spark plug wrench (or socket) to secure the spark plug.

 Tighten the spark plug

 

 

Replace the spark plug boot.

 Replace the spark plug boot

 

 

  22. Reinstall the carburetor mounting assembly (with fuel tank).

Verify that the rubber tank isolator is properly positioned on the engine.

Make sure the isolator is in place

 

 

Install the fuel tank onto the engine.

 Install the fuel tank

 

 

Install the second tank isolator (rubber) onto the carburetor mounting assembly.

 Install the second rubber isolator

 

 

Verify that the crankcase gasket is properly positioned on the bottom of the carburetor mounting assembly.

 Inspect the gasket

 

 

Install the carburetor mounting assembly onto the engine.

 Install the carb plate

 

 

Secure the carburetor mounting assembly (and the fuel tank) to the engine with the (4) screws.

 Secure the carb plate

 

 

  23. Reinstall the muffler.

Install the (2) mounting screws to the muffler assembly.

 Install the screws

 

 

Install the exhaust gasket onto the muffler (the screws will help keep it aligned).

 Install the gasket

 

 

Install the muffler assembly and gasket onto the engine.

 Install the muffler

 

 

Secure the muffler assembly and gasket to the engine with the (2) screws.

 Secure the muffler

 

 

  24. Reinstall the upper shaft and clutch drum housing to the engine.

Thread the throttle cable through the engine housing and through the opening on the carburetor mounting assembly.

 Thread the throttle cable into the housing

 

 

Reconnect the upper shaft and clutch drum housing to the engine.

 Connect the shaft

 

 

Secure the upper shaft and clutch drum housing with the (4) screws.

 Secure the shaft

 

 

  25. Reinstall the carburetor.

Install the carburetor gasket.

 Install the gasket

 

 

Install the throttle cable onto the throttle linkage of the carburetor.

 Connect the throttle cable

 

 

Install the incoming fuel line to the lower carburetor inlet.

 Connect the lower fuel line

 

 

Install the (primer) fuel line to the upper carburetor inlet.

 Connect the upper fuel line

 

 

Install the carburetor mounting screws onto the choke plate and lever.

 Install the screws

 

 

Secure the carburetor (and choke plate) to the engine with the (2) screws. Note that the choke lever and the wavy washer must be properly aligned before tightening the upper screw.

 Secure the carburetor

 

 

  26. Reinstall the rear cover.

Reinstall the rear cover onto the engine.

 Install the rear cover

 

 

Secure the rear cover with the (4) screws.

 Secure the rear cover

  The Finish

You don't have to leverage your savings to level your lawns. As you just learned, repairing your own equipment is easy when you follow our step-by-step guides. Not only did you restore trimmer functionality at a fraction of the cost of replacement; you have taken the edge off of future repairs, wherever you may find them.

Find your next fix here.   [top]

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