Long copy and paste post from a PDF. E10
Found this on the internet searching for pictures of foul plugs and low and behold...Some of you might have read this already. Interesting stuff.
Early in May of 2008, I purchased a 1991 model Husqvarna 3120 chainsaw with a recent shop
rebuild to power a 72-inch Alaska Mill. Fueled with fresh mixed gas according to
manufacturer’s specifications, the saw’s 42- inch bar easily buried itself into a huge black
walnut log. But before the second cut was finished, the engine casing began to smoke, and the
saw was “toast.”
At the shop, the factory-trained mechanic determined overheating/detonation had caused
engine failure and added my 3120 to the growing list of recent saw failures. It was suspected
the failures were related to ethanol, especially since Oregon recently mandated E10 at all their
pumps.
Is Ethanol the Problem?
An informal survey of a dozen northwest Oregon saw shops revealed that all the shops had
noticed fuel line and carburetor diaphragm issues related to ethanol. About half of the shops
reported experiencing saw engine failures and suspected ethanol as the culprit.
Over the next few weeks, I sought out industry experts to try to separate myths from facts. The
following information is a summation of interviews with Randy Scully, STIHL Inc. product
service manager, James McNew, vice president technical affairs Outdoor Power Equipment
Institute (OPEI), and Robert Reynolds, president of Downstream Alternatives, a fuels
consulting company. All agreed that ethanol impacts chainsaw engine operation.
Engine Operation and Failure Modes
Chainsaws use precision engineered, high performance 2-cycle engines revving at 12,000 to
14,000 rpm. The proper mixture of the correct 2-cycle engine oil and gasoline provides fuel to
power the engine and carries essential lubrication to the rapidly moving parts. High speeds,
friction, and combustion processes all generate heat that must be removed to avoid damaging
the engine.
Cooling a chainsaw occurs in two ways. Cylinder fins increase surface area available for
transferring heat as the fan forces outside air over the cylinder/fins to remove heat. Heat is also
dissipated by the inflow of cool air and fuel. As the air and fuel enter the combustion chamber,
it absorbs heat energy prior to combustion and exiting exhaust gases carry away heat as well.
Most damage to chainsaw cylinders and pistons is directly related to engine overheating due
to either excessive heat generation and/or failure to remove heat produced during operation.
Lean Seizure — This common failure mode occurs when the oxygen-to-fuel mix ratio is too
lean and leads to overheating. Several factors contribute to lean seizure — a lean fuel-to-air
mix burns hotter, saws runs faster increasing friction heat, lower fuel flow provides less cooling
and reduced lubrication.
Increased heat production, combined with reduced cooling, leads to piston/cylinder scoring
and engine failure. (Typically, a lean seizure is evidenced by scarring damage on the exhaust
side of the piston and cylinder where temperatures are the hottest.)
The term “lean” is also used to refer to too little oil in the gas mixture. A “lean” oil-to-gas mixture
results in more friction heat due to inadequate lubrication of moving parts and can lead to rapid
damage to engine components.
Detonation or Pre-Ignition — Another heat related failure mode is detonation (sometimes
called “pre-ignition”). Under normal operating conditions, the sparkplug ignites the fuel mix,
initiating a controlled burn that moves through the combustion chamber. This “burn” produces
a smooth power stroke to drive the piston down at the proper time.
When overheated, excessive combustion chamber temperature can ignite fuel independent
from the spark plug. When this happens, the two “fires” rapidly burn toward one another and
collide creating even more heat and disrupting engine timing. The stress on the engine’s
moving parts is greatly multiplied and may cause catastrophic failure. (Detonation failure is
usually evidenced by physical piston/ cylinder damage and scarring at a location other than
the exhaust side.)
Detonation is also a function of the fuel’s octane level. Generally speaking, octane is the
characteristic of a fuel to resist detonation. In automobiles, low octane fuel causes “knocking”
(detonation) in the engine.
Since automobile engines operate at relatively low rpm, the knocking is of much less
consequence than in high speed chainsaw engines. For most operators, the chainsaw’s high
rpm and louder ambient noise level mask the occurrence of detonation until symptoms of
failure become evident. Many factors may contribute to overheat situations, including dirty
cylinder/fins, plugged cooling air intake, improperly vented fuel tank, improperly adjusted
carburetor, too little oil in fuel, wrong type of oil in fuel, air in-leakage, or an overheated spark
plug.
Now Add Ethanol
Modern chainsaws are designed to run on gasoline (E0), but manufacturers offer assurances
that they will operate properly on E10. However, it’s no secret that mixing ethanol with gasoline
alters the characteristics of the fuel and potentially contributes to 2-cycle engine failures. Older
equipment may be at a significantly greater risk for damage.
Increased Oxygen — Ethanol’s higher oxygen content leans the fuel-to-air mix causing saws to
run faster and hotter. The leaner fuel is less effective at lubricating, further increasing heat
through friction. Ethanol is also a less effective cooling medium than gasoline. All of these
factors make chainsaws run hotter on E10 than they do on E0 — yet properly adjusted modern
saws should function properly without failure when using gasoline mixed with 10 percent
ethanol.
Fuel Separation — When contaminated with .5 percent water (about four teaspoons per
gallon) ethanol will separate from gasoline. This is called phase separation.
Phase separation is most likely to occur when first introducing E10 into a storage tank
previously used for non-ethanol fuels. If not thoroughly cleaned and dried before filling with
E10, water already in the tank may cause phase separation. Tests have shown that in fuel
stored at 70 degrees at 70 percent humidity it will take more than 100 days before the ethanol
will absorb enough water from the air to cause phase separation. However, repeated heating
and cooling of storage containers, or exposing them to moisture, may increase risk of phase
separation.
Ethanol acts as a solvent — When operating a chainsaw on E0, residue can build up in the
fuel system. The introduction of the ethanol, which acts as a solvent, dissolves the residue and
allows it to pass through the carburetor, plugging the jets and preventing the carburetor from
properly mixing the fuel and air. This again leads to a lean air-to-fuel ratio that can cause a
failure. It is important to thoroughly clean the fuel system, tank, fuel lines, and carburetor,
before switching to the E10 fuel.
Pre-existing Problems Amplified
Although using E10 gasoline should not cause a chainsaw to fail, equipment with pre-existing
problems, not yet serious enough to cause failure when using E0, may fail when the switch is
made to E10.
A chainsaw adjusted to run hot and fast on E0, may run too hot when fueled with E10 if the
fuel/air mix is not adjusted to compensate. An existing air leak, grime on cylinder fins, air flow
obstructions, or any other problem that either increases heat production or hinders heat
removal, may elevate a latent problem into a source of failure.
Making the Switch to E10
Switching from an E0 to an E10 fuel should be made in conjunction with verification of proper
operation of the chainsaw by giving special attention to air cooling systems and fuel flow.
