Mowing is enough of a
chore without having to deal with a rough-running, poor-cutting lawn mower.
With just a few bucks’ worth of parts and a couple of hours’ work, you can get
your lawn mower in prime shape to start the mowing season. We’ll show you how
to drain the old gas, replace the air filter, put in a new spark plug, change
the oil and sharpen the blade—tasks that will keep your gas-powered mower
starting easy, running smooth and cutting clean.
Click Image to enlarge.
Add fresh gas at the start of the
season
Fuel system problems top
the list of lawn mower malfunctions. Many of these, like gunked-up carburetors,
are often caused by gasoline that’s been left in the mower too long. Although
fall is the best time to take preventive measures (see “Storing Your Lawn Mower
for the Winter,” p. 87), you can at least get off to a good start in the spring
by replacing the old gas in your tank with fresh gas.Photo 1 shows
one method.
Gasoline is highly
flammable. Work outdoors or in a well-ventilated area away from sparks and
flame. Wipe up spills immediately and store gas in approved sealed containers.
To dispose of the old gas, call your local hazardous waste disposal site for
instructions.
Most mowers have a mesh
screen over the outlet at the bottom of the tank. If you can see the screen
through the filler hole, use an old turkey baster to suck up dirt and debris
that may be covering it.
Change your oil regularly
Changing the oil in your
lawn mower takes about 15 minutes and costs less than $2. That’s time and money
well spent considering that changing oil at the recommended intervals will
greatly extend the life of the engine. Most engine manufacturers recommend an
oil change at least every 25 hours of operation or every three
months.
Older mowers have a fill
plug close to the mower deck. Fill this type until oil reaches the threads of
the refill hole. Two-cycle engines that use a gas/oil mix for fuel don’t have
an oil reservoir on the engine and don’t require oil changes.
Before you drain the old
oil, run the mower a few minutes to warm the oil and stir up sediment. Then
disconnect the spark plug, drain the old oil and add new (Photos 1 – 4). Use SAE 30 W oil
(check your owner’s manual). There are two ways to drain old oil: through the
filler neck (Photo
3) or out the drain plug in the bottom of the engine (Photo 5). It’s
quicker and easier to drain the oil through the filler neck if your mower has
one. If you have an older mower without a filler neck, locate the drain plug on
the bottom of the engine and remove it to drain the oil. Pour used oil through
a funnel into a plastic milk jug or other container and label it for
recycling.
Whenever you tip a lawn
mower up on two wheels (Photo
3) to work on the underside,
only lift the side
with the air cleaner. This prevents
oil from running into the carburetor and soaking the air filter. Also, if your
lawn mower has a fuel valve, turn it off.
Remember to check the
oil level occasionally between oil changes, setting the mower on a level
surface. Top it off as needed. Newer mowers have dipsticks with markings that
indicate when to add oil. Don’t overfill. Check your manual for instructions to
see whether the dipstick should be fully screwed in or just set in when you’re
checking the level. If you accidentally add too much oil, follow the procedure
shown in
Photos 3 and 5
to drain some out.
CAUTION
Always
disconnect the spark plug wire from the spark plug (Photo 6) before reaching
under your mower.
Add pep with a new spark plug
Often a new spark plug
will make a big improvement in the way your engine starts and runs. Spark plugs
are so cheap (less than $3) and easy to install that it’s good insurance just
to replace your plug every spring. Check your owner’s manual for the correct
spark plug, or take the old plug with you to the store to match it
up.
New spark plugs are
factory set with a .030-in. gap between the electrodes at the tip of the plug.
Inspect the plug when you buy it to make sure there’s a gap about the thickness
of a matchbook cover. If there’s no gap, the plug may have been dropped and
damaged. Choose another one.
If you don’t own a
socket wrench set with a 3/4-in. or 13/16-in. deep socket for changing the
spark plug, pick up an inexpensive ($3 to $4) spark plug wrench (photo
above).
Don’t suffocate your mower—change the air
filter
Air filters are cheap
and easy to replace. Dirty air filters choke the engine, causing it to run
poorly and lose power. If your lawn is dry and dusty, check the filter after
every few mowings. Otherwise, check it a couple of times during the season.
Replace it when it starts to get plugged with dirt and debris. One common test
is to shine a flashlight through the filter. If you can’t see the light through
the filter, replace it with a new one.
Most newer mowers have
pleated paper filters that are either flat or cylindrical (Photo 9), while
many older mowers have foam filters (Photo 10). Both types of
replacement filters are readily available for $3 to $6 at lawn mower retailers,
hardware stores and home centers. Take your old filter along and have your
mower manufacturer’s name and model number handy.
In a pinch, you can wash
foam filters in a solution of laundry detergent and water and allow them to air
dry. But since replacements only cost about $3, it’s best to just buy a new
one. In either case, saturate the foam filter in motor oil and squeeze out the
excess before installing it (Photo 11).
Storing your lawn mower for the winter
Gasoline
left in your mower during storage can deteriorate and leave gum deposits that
clog the fuel system. There are two storage methods: completely draining the
system or leaving it filled with fresh, stabilized gasoline.
Most
manufacturers of newer mowers recommend draining the gas completely. Do this by
opening the drain valve or drain bolt on the carburetor bowl and draining the
gas into a container. If your carburetor doesn’t have a drain valve, check with
the manufacturer or lawn mower repair center for
instructions.
Older
lawnmowers with a foam filter and carburetor that’s screwed to the top of the
gas tank should be filled with stabilized fuel for the winter. Purchase a
container of fuel stabilizer, available at hardware stores, home centers, gas
stations or lawn mower service centers, and mix as recommended with fresh gas.
Fill the empty lawn mower tank with the stabilized gas and run the mower for
about 10 minutes. Then top off the fuel tank with stabilized gas and shut the
fuel valve. Check your owner’s manual for storage
instructions.
Keep your blade sharp for the best
cut
A sharp blade will make
your lawn mower cut like new. The cleanly cut grass will look better, and your
mower won’t bog down every time you hit a thick spot. If your lawn is rough and
you mow over rocks and dirt spots, your blade may need to be sharpened several
times during the season. Otherwise, once or twice should be plenty. Keep on top
of the sharpening task by tuning up the blade with a mill bastard file whenever
it starts to dull (Photo
14). Once the edge of your blade becomes rounded or chipped, it’s a
lot faster to use a grinder to restore the edge (Photo 13). Most
hardware stores and lawn mower mechanics will sharpen your blade for $3 to $5,
but you have to remove it for them. Use a permanent marker to mark the bottom
of the blade and other parts like washers and mulching accessories. Then number
them so they’ll be easy to reinstall in the right sequence and
orientation.
Inspect the blade for
cracks or worn-thin areas every time you sharpen it, paying special attention
to the area at the base of the upswept section (upper right
photo). Replace the blade with a new one if the metal is worn thin
or cracked ($10 to $15). You’ll find the best selection of new blades at a lawn
mower service center or your lawn mower retailer.
It’s surprising how
quickly you can put a new edge on a blade with a sharp file. Buy a 10-in. mill
bastard file ($6) and keep it sharp by protecting it from moisture and contact
with other tools when you’re not using it.
Grinding is much quicker
than filing, but you have to follow a few safety precautions and avoid
overheating and ruining the blade. Wear goggles or a full-face shield when
grinding. Never wear loose clothes or jewelry that could get caught in the
wheel. Keep your hands and face out of the path of the sparks, and make sure
there are no flammable liquids or spilled gasoline nearby.
It’s easy to overheat
blades on a grinder by applying too much pressure or leaving the blade in one
spot too long. Overheated metal loses its temper and won’t stay sharp. You’ll
know if you’ve overheated the metal by the change in color from silver to dull,
blackish blue. Proper grinding technique (Photo 13) and dipping the blade
frequently in water will help keep it cool.
Some maintenance is best left to the
pros
The basic maintenance
tasks we show above will go a long way toward keeping your mower in good
running condition. But there are two more items that would normally be included
in a professional tune-up. The first is disassembly and cleaning of the
carburetor and linkage. This may be necessary if you’ve left untreated gas in
the tank over the winter and the lawn mower won’t start or runs poorly. This
repair requires some mechanical experience.
Cleaning grass and
debris from the engine’s cooling fins (the cooling fins are the metal ridges
that cover the engine) is another maintenance task that should be performed
periodically. On mowers with exposed cooling fins, this is an easy
do-it-yourself job. Use a stiff-bristle brush to clean gunk from between the
fins. On many newer mowers, however, the plastic or metal covering on top of
the engine has to be removed first, which may also require disconnecting the
fuel tank. Use a flashlight to inspect the cooling fins under these covers. If
they look clogged, you’ll have to decide if you’re up to the challenge or would
feel more comfortable letting a pro handle the job. Most lawn mower mechanics
charge $80 to $120 for a basic lawn mower tune-up that includes all the items
in this story, plus cleaning and adjusting the
carburetor.
Click Image to enlarge.
1 Using an old turkey baster, suck old gas from
your tank. Squirt it into a container approved for gas storage and label it as
old gas. Refill the tank with fresh fuel.
2 Seal the gas tank by removing the gas cap and
covering the opening with a plastic bag. Screw the cap back on over the plastic
bag.
3 Remove the dipstick from the oil filler tube
and tip the mower to drain the oil. Pour the used oil into a plastic milk jug
or similar container and recycle it.
4 Refill the engine with clean oil. Most engines
require about 20 ozs. (5/8 quart). Insert the dipstick and check the oil level.
Add oil if needed but don’t overfill.
ALTERNATE DRAINING
METHOD
5 Unscrew the plug located on the bottom of the
engine and allow the oil to drain into a pan. Lower the mower down on its
wheels to make sure all the oil drains. Replace the plug, set the mower on a
level surface, and fill the engine with clean oil through the filler hole near
the base of the engine.
CAUTION
Always
disconnect the spark plug when you check the blade or remove it for
sharpening.
6 Remove the spark plug wire by pulling it
straight out. If it’s stuck, try twisting it slightly as you pull. Wipe off
dirt from the area. Use a 3/4-in. or 13/16-in. deep socket or spark plug wrench
to unscrew the old spark plug. Turn the wrench
counterclockwise.
7
Install the new spark plug by turning it clockwise two or three
complete revolutions by hand before switching over to the spark plug wrench to
tighten it. Don’t over-tighten the spark plug. Manufacturers recommend
tightening the plug about a half turn after it seats to compress the new
washer. Complete the job by pressing the plug wire onto the
plug.
PLEATED PAPER AIR
FILTERS
8
Locate the air filter near the carburetor. Unscrew, unsnap or
twist off the cover to remove the old filter.
9 Remove the old air filter and replace it if
it’s dirty. Wipe grass and dirt from the filter cover and the mounting area
with a clean cloth before installing the new filter. Be careful not to let dirt
fall into the carburetor.
FOAM AIR
FILTERS
10
Unscrew or unhook the cover and pull out the old filter. Wipe the
filter cover parts with a clean rag to remove dirt and grime.
11 Pour about 1/4 cup of clean motor oil over the
new foam filter. Wrap the filter in a clean cloth and squeeze it firmly to
distribute the oil evenly and remove any excess. Install the filter, making
sure the foam lip covers the top of the filter holder. Replace the cover and
tighten the screw.
Click Image to enlarge.
12 Disconnect the spark plug wire, turn off the
fuel valve and seal the gas tank (Photo 2). Then clamp a block of wood to the
lawn mower deck with the sharp edge of the blade against the block. Remove the
blade by turning the large nut counterclockwise with a socket
wrench.
13 Sharpen blades with nicks or rounded cutting
edges on a grinder. Hold the blade firmly and tilt it so the grinding wheel
contacts it at the original angle (about a 30-degree bevel). Move the blade
steadily across the grinding wheel while applying slight pressure. Dip it in
water after each pass to cool it.
14 File previously ground or slightly dulled
blades with a 10-in. mill bastard file to hone the edge. Align the file with
the angle of the blade and push down across the blade. You should feel the
teeth cutting the metal. Maintain the same angle throughout the stroke. Files
cut only on the push stroke. Use a file card to clean built-up metal from the
file’s teeth.
Click Image to enlarge.
15
Balance the blade on a balancing cone ($4 at hardware stores)
before reinstalling it. Working on a level surface, set the blade on the cone
and eyeball each end. Mark the heavy end. Grind some metal from the blunt part
of the heavy end. Recheck the balance and repeat until the blade balances.
Reinstall the blade, washer or other parts in the reverse order you removed
them.
Art
Direction • BECKY PFLUGER
Photography • BILL ZUEHLKE
Consultants • JIM CARLSON
