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Two-cycle Engine Applications
and Lubrication Needs
Two-cycle engines can be found nearly
everywhere these days. They are used in dozens of applications
and in a wide variety of designs for everything from work
and recreation to power generation. Two-cycle engines have
design differences and operate under conditions that require
different oil chemistries than their four-cycle counterparts.
In order to recommend a lubricant for a two-cycle engine,
one needs to know how this engine operates, why it is used
in place of a four-cycle engine and where and in what type
of applications it is used.
What is a two-cycle engine?
The terms "two-cycle" and "two-stroke"
are often inter-changed when speaking about two-cycle engines.
These engines derive their name from the amount of directional
changes that the pistons make during each power stroke. Internal
combustion engines are used to produce mechanical power from
the chemical energy contained in hydrocarbon fuels. The power-producing
part of the motor's operating cycle starts inside the motor's
cylinders with a compression process. Following this compression,
the burning of the fuel-air mixture then releases the fuel's
chemical energy and produces high-temperature, high-pressure
combustion products. These gases then expand within each cylinder
and transfer work to the piston. Thus, as the engine is operated
continuously, mechanical power is produced. Each upward or
downward movement of the piston is called a stroke. There
are two commonly used internal combustion engine cycles: the
two-stroke cycle and the four-stroke cycle.
|Two-cycle motors deliver one power
impulse for each revolution of the crankshaft.
How are two-cycle engines different
from four-cycle engines?
The fundamental difference between
two-cycle engines and four-cycle engines is in their gas exchange
process, or more simply, the removal of the burned gases at
the end of each expansion process and the induction of a fresh
mixture for the next cycle. The two-cycle engine has an expansion,
or power stroke, in each cylinder during each revolution of
the crankshaft. The exhaust and the charging processes occur
simultaneously as the piston moves through its lowest or bottom
In a four-cycle engine, the burned gasses
are first displaced by the piston during an upward stroke,
and then a fresh charge enters the cylinder during the following
downward stroke. This means that four-cycle engines require
two complete turns of the crankshaft to make a power stroke,
versus the single turn necessary in a two-cycle engine. In
other words, two-cycle engines operate on 360 degrees of crankshaft
rotation, whereas four-cycle engines operate on 720 degrees
of crankshaft rotation.
|A four-cycle engine requires four
strokes of the piston (two up and two down) and two revolutions
of the crankshaft to complete one combustion cycle and
provide one power impulse.
Where are two-cycle engines
Two-cycle engines are inexpensive to
build and operate when compared to four-cycle engines. They
are lighter in weight and they can also produce a higher power-to-weight
ratio. For these reasons, two-cycle engines are very useful
in applications such as chainsaws, Weedeaters, outboards,
lawnmowers and motorcycles, to name just a few. Two-cycle
engines are also easier to start in cold temperatures. Part
of this may be due to their design and the lack of an oil
sump. This is a reason why these engines are also commonly
used in snowmobiles and snow blowers.
Some advantages and disadvantages
of two-cycle engines
Because two-cycle engines can effectively
double the number of power strokes per unit time when compared
to four-cycle engines, power output is increased. However,
it does not increase by a factor of two. The outputs of two-cycle
engines range from only 20 to 60 percent above those of equivalent-size
four-cycle units. This lower than expected increase is a result
of the poorer than ideal charging efficiency, or in other
words, incomplete filling of the cylinder volume with fresh
fuel and air. There is also a major disadvantage in this power
transfer scenario. The higher frequency of combustion events
in the two-cycle engine results in higher average heat transfer
rates from the hot burned gases to the motor's combustion
chamber walls. Higher temperatures and higher thermal stresses
in the cylinder head (especially on the piston crown) result.
Traditional two-cycle engines are also not highly efficient
because a scavenging effect allows up to 30 percent of the
unburned fuel/oil mixture into the exhaust. In addition, a
portion of the exhaust gas remains in the combustion chamber
during the cycle. These inefficiencies contribute to the power
loss when compared to four-cycle engines and explains why
two-cycle engines can achieve only up to 60 percent more power.
How are two-cycle engines lubricated?
Two-cycle motors are considered total-loss
type lubricating systems. Because the crankcase is part of
the intake process, it cannot act as an oil sump as is found
on four-cycle engines. Lubricating traditional two-cycle engines
is done by mixing the oil with the fuel. The oil is burned
upon combustion of the air/fuel mixture. Direct Injection
engines are different because the fuel is directly injected
into the combustion chamber while the oil is injected directly
into the crankcase. This process is efficient because the
fuel is injected after the exhaust port closes, and therefore
more complete combustion of fuel occurs and more power is
developed. Direct injection engines have a higher power density
than traditional two-cycle engines. Because the oil is directly
injected into the crankcase, less oil is necessary and lower
oil consumption results (80:1 range). Direct Injection motors
have higher combustion temperatures, often up to 120 degrees
F. They also require more lubricity than traditional two-cycle
AMSOIL Synthetic 2-Cycle Oils
Synthetic 2-Cycle Oils are formulated to provide maximum
performance in all types of two-stroke applications. Even
2-Cycle Oils have been optimized for specific applications,
they are multi-functional and recommended for use in many
Related Article: A
Look at Snowmobile Exhaust Power Vavles
Why Motor Oil Deteriorates
It is common knowledge
that, at some point, engine oil must be changed. It's something
that is preached relentlessly to vehicle owners by vehicle
manufacturers, quick lubes and oil companies. But consumers
are widely unaware of what exactly makes oil changes necessary.
Many factors contribute
to a motor oil's demise, but it is essentially the accumulation
of contaminants in the oil and chemical changes in the oil
itself that make a motor unfit for further service. With time,
it is inevitable that the oil will be contaminated by dirt
or sludge, or succumb to the extreme pressures or temperatures
found inside an engine. AMSOIL Motor Oils are formulated with
the industry's most advanced synthetic base stocks and additive
packages to combat the forces that deteriorate conventional
What is the NOACK Volatility
Volatization is a term used to describe
what happens to a fluid as it is heated to the point it begins
to "boil off." Upon reaching a certain temperature,
oil will begin to lose some of its lighter weight molecules
as they "boil off" and leave heavier weight molecules
behind. Not only does this cause higher oil consumption, this
process can also cause increased viscosity making the oil
more difficult to circulate through the lubrication system.
Quality Takes Priority at AMSOIL
The AMSOIL chemical
laboratory plays an important role in the daily operations
at AMSOIL headquarters. The lab fulfills tech service requests,
performs competitor testing and comparisons, and works on
the research and development of products at AMSOIL. One of
the most important jobs at the lab is quality control. AMSOIL
is known for formulating high-quality products and the AMSOIL
chemists ensure that everything coming in and going out meets
AMSOIL standards. How do they do it? (read
Synthetic Motor Oils offer the longest drain intervals
on the market, unsurpassed protection and performance that
effectively extends equipment life and improved fuel economy,
saving customers money at the pump and reducing the nation's
dependence on foreign oil.
INC. warrants that the use of its lubricants will not cause
mechanical damage to any mechanically sound equipment when
AMSOIL INC. products are used in full compliance with the
company's recommendations and instructions."
synthetic motor oils are formulated to surpass engine test
specifications, offering protection far greater than competing
motor oils for extended drain intervals. Most synthetic oil
manufacturers make no claim to extended drain intervals, deferring
to the maintenance schedule provided by the vehicle manufacturer.
With its unparalleled oil and warranty program, AMSOIL offers
consumers unprecedented protection and economics.
More than 20 years
ago, AMSOIL began using the NOACK volatility test as a comparison
tool and measurement of quality. Back then, nearly every oil
tested side-by-side with AMSOIL synthetic motor oils failed,
and those that passed barely squeaked by. Other oil companies
paid no attention to NOACK results until Ford Motor Company
made it a requirement for service fill oils, validating what
AMSOIL had said all along.
NOACK Volatility Test
Volatility Test determines the evaporation loss
of lubricants in high temperature service. The more
motor oils vaporize, the thicker and heavier they become,
contributing to poor circulation, reduced fuel economy
and increased oil consumption, wear and emissions. AMSOIL
Synthetic Motor Oil resists high temperature volatization
better than other motor oils. AMSOIL Synthetic Motor
Oil maintains peak fuel efficiency and reduces oil consumption
AMSOIL Now An ISO Certified
received ISO 9001:2000 certification of our Quality Management
System (QMS). NSF International Strategic Registrations is
the registrar that has verified our QMS meets the requirements
of the ISO 9001:2000 standard, the most widely utilized quality
standard throughout the world for quality management systems.
ISO standards are used by over 300,000 companies worldwide
setting rigorous standards for businesses, government and
is applicable to any manufacturing and service organization
providing a framework for system development that focuses
on the customer, quality system performance and ongoing improvement.
AMSOIL received ISO 9001:2000 registration under the scope:
synthetic lubricants blending, packaging, and other fulfillment
directly associated with lubricant product.
certification puts AMSOIL in line with some of the most efficient
companies in the world. It is further assurance that the products
and services AMSOIL provides will continue to maintain the
high level of quality the company always demanded.
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