Does your saw not start, does it start and
die? If so, you might need a new piston ring. The piston ring is attached to the piston,
it stills the piston to the cylinder, producing compression as the engine operates. As the ring wears, the seal will be lost and
compression will drop. Under optimal conditions, the piston ring
will wear very slowly. Depending on the amount of use that the saw
receives, the ring may last a lifetime. Most problems with piston ring wear are the
result of other issues with the saw. Dirt and dust will quickly cause piston ring
wear. If the air and fuel filter aren’t properly
maintained, dirt or dust can enter the engine and cause premature ring failure. During normal operation, the piston ring doesn’t
actually contact the cylinder, there’s a thin coating of oil between the ring and the cylinder
wall, only a few molecules thick. If the fuel use doesn’t contain the proper
mix and type of oil, the ring will make contact with the cylinder, the steel piston ring will
quickly heat up and expand, which causes severe damage to it and the aluminum cylinder. Because the piston ring and the cylinder work
as a pair, anytime there’s ring damage, there will likely also be cylinder damage, so both
components should be carefully inspected. You can test for piston ring damage with the
compression tester, the tester attaches to the spark plug hole and rates the amount of
compression produced by the engine. You will need to refer to the manufacturer’s
specifications to find the compression range for your engine, as it does vary. Replacing a piston ring is a more advanced
repair, but if you have some small engine repair experience and the right tools, it
is a repair that you can do yourself, and I’m going to show you how. Hi, I am Mark Sodja. Do it yourself repairs like these are easier
than you might think, from lawn machines to cordless drills, kitchen mixers, outdoor grills. Our how-to videos walk you through each repairs
from start to finish, so doing it yourself means never having to do it alone. Let’s get started. I’ll begin by removing the side cover, the
chain and the bar. Now we remove the top cover, it’s held in
place with three screws. Now we remove the starter assembly. Now we remove the top handle. Now we remove the clutch drum. Next I’ll remove the clutch, there’s a number
of ways you can do this, you can just use a pair of adjustable pliers, if you do that,
it’s a good idea to put a rag over the clutch so you don’t damage it with the pliers, and
also, you’ll need to bind the piston so the crankshaft can’t spin. To do that, you remove the spark plug and
then insert a short length of starter rope into the cylinder and that will bind the piston
between the rope and the top of the cylinder. The better method is to use a clutch removal
tool, there’s a couple of pins that will bind up with tabs on the clutch, you place the
tool over the shaft and then place a socket onto the tool and use a ratchet wrench to
remove it. Again, you’ll need to bind the cylinders if
you use this, or I think the better way is to use an impact wrench if you have one. With the impact wrench, the compression inside
the cylinder will be great enough that you don’t need to bind up the piston, just simply
the compression will keep the engine from turning over. Next I’ll remove the brake assembly, there’s
a spring inside the brake that is under tension when the brake is released, so to safely remove
this, you need to make sure that the brake is locked. Now I can remove the side cover. Now I can remove the oil pump assembly, it’s
held in place with two screws, and I’ll remove the oil pump gear. Now we remove the carburetor, I’ll pull the
trigger so I can access the end of the linkage and pull it away from the trigger. Now I need to pull the wires away from the
cylinder, they’re held in place with this wire clip, and I’ll go ahead and remove that,
and then I can pull away the wires. Now we remove the flywheel. Again, I’m going to use an impact to remove
the flywheel nut, but if you don’t have an impact, you can use a ratchet wrench, you
will just need to bind the cylinder so that the crankshaft can’t spin. If the flywheel is stuck on the taper, what
you want to do is thread the nut back onto the shaft, not all the way, though, you don’t
want any threads extending out past the nut. Then I’ll use a socket on the nut, I’ll strike
the socket with a hammer and the flywheel should pop free. There we go, we remove the nut, and the flywheel
comes free. Now we remove the remaining cylinder assembly
from the saw, the top half of the cylinder is connected to the crankcase with the same
screws that hold the engine to the base, so I’ll remove those screws. Okay, now I should be able to pull the cylinder
away from the piston. Now we remove the piston ring from the piston,
before I do, you’ll notice at the piston ring end gap, there’s a radius milled into the
ring. I’m just going to take note of the direction
of that radius, the radius is pointed up, so to install the new ring, I install it the
same way. Let’s carefully work the ring around the piston
and out. Now use a rag to clean the piston ring groove,
just want to get any oil and tar or other debris that might be in that groove. Depending on how dirty it is, you might want
to use a little carburetor cleaner to help with this, this one’s not too bad. Now I can install the new ring, I’ll place
one end of the ring into the groove, and then just work around the piston, slightly spreading
the ring and pushing it down. You don’t want to spread the ring too much,
these are very brittle, you’ll break it into two pieces, just like that. The joint between the cylinder and the crankcase
is sealed with some liquid gasket, before we reassemble this, I need to clean off all
the old liquid gasket to get ready for the new. I’ll use a razor blade to carefully scrape
the gasket material away. Now we will install a bead of liquid gasket
around all of the sealing surfaces on the crankcase and the cylinder. This is a case where less is usually better. On the cylinder side, I need just a small
bead up against these shoulders for the bearings. Now I can install the new piston assembly,
before I slide into the cylinder, I’ll again add a little bit of oil to it so it’s not
dry when the saw is started. Now I can slide the piston into the cylinder,
before I do, I want to make sure that I have the porting on the piston pointed towards
the carburetor. I’ll line up the piston ring with the end
gap pin and then insert the piston into the cylinder. As I bring the assembly down, I’ll seat the
bearings into the liquid gasket, and now I can replace the crankcase. This will get snugged up when we install the
engine back into the frame. Now we can begin reassembling the saw, this
is one of the clips that secure the top cover. If this clip on the front of the saw has fallen
out, you’ll want to make sure you reinstall it now because you won’t have another chance. Now I’ll place the engine back into the frame. Just want to be careful that the crankcase
doesn’t come free from the cylinder as I do this. Now it’s in place, I can re-secure it with
the bolts. I’ll get each of the bolts started, now just
work my way around the engine, slowly bringing the two halves of the engine back together,
the cylinder and the crankcase. I don’t have an exact torque spec for these
bolts. What I want to accomplish is just making a
good seal with that liquid gasket so they don’t need to be super tight. Basically, just hand tight with a screwdriver
is all it’ll take. That ought to do it. Now reinstall the flywheel, make sure I line
up the key with the groove in the shaft. Because the way the engine is mounted to the
frame, there’s quite a bit of play, and that can change the gap between the ignition coil
and the flywheel, which it has, as you can see the flywheel is now rubbing against the
ignition coil. I need to reset that gap. To do that, I’ll just loosen the screws on
the ignition coil, pull the coil away from the flywheel, I’m actually going to move the
magnets away from the coil temporarily. Now I’m going to use a gap gauge to set the
proper gap. It should be 0.014 inch. If you don’t have one of these, usually a
good heavy business card will be about the same. Bring the magnet back around, Now the gapping
tool is stuck between the ignition coil and the magnet on the flywheel, and I’ll tighten
the screws back down and remove the gapping tool. Now reinstall the oil pump gear. Get it started on the shaft and then it’s
just a matter of using a screwdriver to slowly push it onto the shaft as the spring expands
open. Now I just want to work it onto the shaft
until it’s centered in the flat portion of the shaft. Now like that. Now install the oil pump. Now I can reinstall the chain brake assembly. I’ll line it up with the housings and then
you might need to just slightly move the brake lever to get the clutch to line up, just like
that, and now I can secure it with the screws. Now the clutch and the clutch drum. Need to release the brake to get the clutch
drum in place. Next comes the carburetor. Slide the linkage back into place, and we’ll
go ahead and install the choke lever. Another of my top cover clips fell off over
here, so I’ll reinstall this now. This will be my last chance to install this
clip. Next is the air filter base. Now I’ll tuck the wires out of the way and
secure them with the clip. Now reinstall the top handle. I’ll place the spark plug boot back onto the
spark plug. Now the starter assembly, now reinstall the
air filter, the air filter cover and the top cover. Now replace the chain guard, yours may or
may not have fallen off and the barn chain. Be sure to check back often for new videos
and expert advice. If you found this video helpful, give us a
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