First off, I did not write this article, but it is very informative and in depth:
Easy Lawnmower Repair"Clouds of white smoke."
This
is one of the common complaints we see at the small engine shop in the
Spring. The complaint is usually the same, "I put the
Tractor/mower/tiller/snowthrower up for the season and it was fine all
of last year. This year I take it out and I start it up and after a
couple of minutes it starts blowing white smoke very heavily. Are my
rings shot?"
Generally billowing clouds of white smoke are from
one of two things. Either the crankcase breather has failed or the oil
is contaminated.
The crankcase breather vents the gases and
excess pressure from the crankcase and sends them through the carburetor
to be burnt in the combustion process. Some breathers are nothing more
than a reed valve that opens and closes as the pressure changes inside
the crankcase from the piston's movement. If this reed breaks, bends or
otherwise fails, then excess oil is pulled into the carburetor and the
result is a lot of smoke. Other breathers are screen or filter type and
when they become too fouled or broken down to function, same result,
lots of smoke.
Diagnosis is done by looking for two things, oil in the air cleaner/
carburetor
and black oil soaked or heavily carboned spark plugs. Since oil is
being fed directly into the cylinder, the plug will foul very quickly
and probably also affect engine performance. Breathers can fail at any
time, often they will fail over the winter as the oil that's built up on
and around them solidifies and just generally plugs things up.
Repair
is a pretty simple matter on many engines, just replace the breather.
You can try turning the reed around on the reed type breathers, but
personally I just replace them. Sometimes all they need is a cleaning
though, so give that a try. Most breathers will run from just a couple
dollars for reeds to maybe twenty dollars although a few that are
incorporated into the valve cover may be upwards of thirty dollars.
Reeds and complete breathers are available from most small engine shops for most engines. Online suppliers such as
Jack's Small Engines, and
M&D are excellent and reliable sources for parts as well.
To
replace a breather, follow the tube or hose from the back of the
carburetor or air filter assembly to where the breather is mounted on
the crankcase. Most are simply attached with two screws but may be under
the flywheel requiring flywheel removal. If it's incorporated into the
valve cover, just replace the valve cover. Some are cartridges that plug
into the valve cover, very easy to replace.
The other common
cause for heavy white smoke, especially in mid-size Briggs and Stratton
and Kohler engines, (12-20hp) is from contaminated oil. The most common
contaminant will be gasoline that has leaked from the carburetor. We
have had at least one engine that had a crankcase full of water, this
was probably a case of sabotage from an irate neighbor.
The diagnosis is simply to examine the oil. It should have little to no smell of
gasoline
and should not be overly thin or muddy brown, gray, white or chunky
like spoiled milk. Do not under any circumstance attempt to start an
engine with oil that fits any of these criteria. The most common cause
of mid-size Briggs and Kohler engine catastrophic failure we see in the
shop is from gasoline diluted oil causing the rod to overheat and break
just above the crank journal.
Gas will get into the crankcase
when you have a carburetor that is leaking past the needle. This leak is
generally caused by either a float problem or other problem keeping the
needle and seat from sealing. If there is gas in the crankcase, then
the recourse is a carburetor rebuild or replacement followed by an oil
change. The reason that this is such a common Spring problem is that if
you leave any gas in the carburetor, it will evaporate and leave behind a
varnish coating that can prevent the float assembly from functioning.
Also, and even more common, the ethanol in today's fuels will ruin
needles and seats, preventing them from sealing the flow of fuel off,
which causes the carburetor to overflow and leak into the crankcase. Gas
can also get into the crankcase from a fuel pump that's leaking, so if
you have a pump, that needs to be checked as well.
These items are often the result of improper storage. I can't stress enough the importance of
proper storage of outdoor power equipment. If
there is water in the oil, then several crankcase flushes with kerosene
and a few oil changes may clean the engine out. However engine
disassembly may also be called for to remove all the muddy deposits and
ensure that the oil channels are cleaned out.
These two items
are the most common causes of a lot of white smoke. We do see a few OHV
engines come in and have blown head gaskets. Usually this is on a Kohler
and often the oil is leaking down onto the exhaust manifold and not
into the cylinder. A leaking valve cover gasket will also do this.
If
the plug isn't fouled out, and the oil is normal, then check closely
for a leak. Spray carburetor cleaner on the head to clean all deposits
off and then run the engine for a bit. Then check for a leak again. Some
talcum powder thrown onto the surface will help to spot a leak as well.
Hopefully one of these will be the solution and you won't be purchasing a new engine. Good Luck!
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