Trimmer Repair – Replacing the Piston & Rod Assembly (Ryobi Part # 753-04367)


Hi, I’m Mark from eReplacementParts.com.
In this video I’m going to show you how to replace the piston in a Ryobi trimmer.
The piston is a central component of your trimmer’s engine. It both provides compression
within the engine, as well as transfers the energy from combustion to the crankshaft,
which creates rotation. The piston assembly is made up of the piston
itself, the piston rings, the connecting rod, and the connecting rod bearing. The most common
reason you need to replace the piston would be worn rings. If you need to replace the
piston, it’s not uncommon to also have to replace the cylinder, as the two work together.
Replacing the piston isn’t the easiest repair, but it’s something you can do yourself if
you follow our instructions. Pistons, as well as many other parts, can be found on our website.
Let’s get started. I’ll begin by removing the rear cover. Now remove the two screws
that secure the carburetor to the engine. Before removing any of the fuel lines from
the carburetor or the lines from the tank, you will want to make sure that you drain
any gas that might still be in the fuel tank. Now I can pull the carburetor away, disconnect
the throttle cable and remove the fuel lines. Now remove the muffler. It’s held in place
with two screws. Now remove the carburetor mounting plate. It’s held in place with
four screws. I’ll also need to thread the throttle cable through the opening in the
mounting plate. As I take this assembly apart, the fuel lines and fuel tank will also come
with it. Now remove the clutch housing and the shaft from the rest of the engine. It’s
secured with four screws. Now remove the clutch drum and the clutch.
Before I do that though, I need to bind up the piston. If I don’t bind the piston,
when I go to remove the screw that secures the clutch drum and the clutch itself, the
crankshaft will simply rotate and I won’t be able to free them. I’ll remove the spark
plug boot and then the spark plug. Now to bind the piston, I’ll insert a piece of starter
rope into the cylinder. The starter rope will coil up and take up all that space inside
the combustion chamber, so that the piston won’t have any travel, and the crankshaft
won’t be able to rotate. Now that the piston is bound, I can remove
the clutch drum and the clutch. Now I can remove the starter assembly. As I pull the
starter away, there’s a wire that leads to the ignition coil. I’ll need to remove
that. Now I’ll remove the flywheel, and the flywheel is secured to the shaft by means
of a taper. There’s a spacer on the crankshaft, I’ll pull that away. To remove it, I’ll
lift up the engine just slightly by the flywheel, and I’ll strike the motor shaft with a rubber
mallet. Beneath the flywheel there’s woodruff key
that indexes the flywheel to the crankshaft, and I’ll remove that key. Now I’ll separate
the cylinder from the crankcase. It’s secured with two screws. I’ll now carefully pull
the piston from the cylinder, and separate it from the crankcase. Now I’ll remove the
cylinder gasket. I’ll use a blade to remove any residue that’s left by the gasket. Now
I’ll install the cylinder gasket. Now we can install the piston.
The first thing I’ll do is apply some 2-cycle oil to the piston itself. This will make it
go into the cylinder a little easier and won’t scratch up the cylinder. Next I’ll compress
the piston rings, and I want to make sure that I have the ring end gaps lined up with
the roll pin in the ring groove, like that. Now install the piston into the cylinder.
The piston needs to be oriented correctly. You’ll notice that one side of the piston
skirt has been cut out. The other side is just straight. This cut out side needs to
go on the side of the cylinder where the ignition coil is. That’ll be the same side that the
counterweight is on the crankshaft. If you get the piston in backwards, the skirt will
strike against the counterweight. So, I’ll hold the rings in compression and
slide the piston into the cylinder. Now I’ll install the connecting rod onto the crankshaft.
I’ll slide the cylinder into the crankcase and secure the cylinder with the screws. Now
I can install the flywheel. First, I’ll place the woodruff key into the slot on the
crankshaft, give that a little tap to seat it in place, and now I can install the flywheel.
I want to make sure that I line up the slot on the flywheel with the woodruff key. The
flywheel may stay a little loose at first, it will get tightened up later when we install
the clutch. Now we can reinstall the starter. First I’ll slide the spacer back onto the
crankshaft. I’ll connect the ignition wire back to the ignition coil, and then I’ll
slide the starter over the crankshaft. As I do, I’ll tuck the wires, the ignition
wires back into the starter housing. With the starter back in place, now secure it with
the screws. I’ll reinstall the base and secure it with its screw. Now install the
clutch. First comes the large washer and then the clutch. If you’ve removed the piece
of starter rope that was in the cylinder to keep the crank shaft from rotating, go ahead
and reinstall that now. And then I’ll tighten down the clutch with a pair of adjustable
pliers. Now install the clutch drum. First comes the
small spacer washer, and then the drum. And I’ll tighten down the internal screw inside
the drum. Now reinstall the spark plug and replace the spark plug boot. Now install
the crankcase cover. As I reinstall the fuel tank, I’ll want to make sure that the rubber
bumper is in place that isolates the tank. There’s also a bumper that goes on the crankcase
cover. Make sure the gasket is in place and slide
the cover onto the crankcase, and now secure it with the screws. Now install the muffler
gasket and reinstall the muffler to the engine. Now reinstall the upper shaft to the engine.
As I do that, I need to thread the throttle cable through the engine housings. I’ll
secure the clutch drum housing to the engine. Now install the carburetor gasket.
Now reinstall the throttle cable back onto the carburetor’s throttle linkage. Now install
the incoming fuel line to the bottom of the carburetor, and the line leading to the primer
bulb on the top. And I’ll secure the carburetor, as well as the choke plate, with the screws.
As I tighten the upper screw, I want to make sure I have the choke plate lined up, as well
as the wavy washer, so it doesn’t get pinched by the screw. Now reinstall the back cover
and secure it with the screws. And now you know how to replace the piston
assembly on your Ryobi trimmer. If you found this video helpful, be sure to give us a thumbs
up and leave a comment.

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