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?

Two-cycle motors deliver one power impulse for each revolution of the
crankshaft. 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.

How are two-cycle engines different from four-cycle engines?

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. 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 center
position.

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.

Where are two-cycle engines used?

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
120F. They also require more lubricity than traditional two-cycle
motors.

NEW AMSOIL "FABULOUS FOUR" 2-CYCLE OILS PROVIDE SECOND-TO-NONE PROTECTION AND PERFORMANCE IN MODERN TWO CYCLE EQUIPMENT

Two-cycle engines remain the workhorses in recreational equipment,
including outboard motors, motorcycles, snowmobiles and personal
watercraft, as well as in lawn and garden applications like lawn
mowers and weed eaters. Design changes over recent years have included
direct fuel injection engines, in which fuel is injected directly into
the combustion chamber, and exhaust power valves, which improve
combustion efficiency at varying RPM. These design changes have
allowed two-cycle engine manufacturers to effectively reduce
emissions, improve fuel efficiency and decrease oil consumption.
Today's two-cycle motors of all types require specialized oil
technology to deliver maximum engine protection, dependable operation
and long service life

As the leader in two-cycle oil technology, AMSOIL has performed
extensive research in developing a new line of revolutionary,
specialized oils called the "Fabulous Four." AMSOIL INTERCEPTOR
Synthetic 2-Cycle Oil (AIT) was the first new oil to be introduced. It
is primarily recommended as an injector oil or at a 50:1 mix ratio in
carbureted, electronic fuel injected (EFI) and direct fuel injected
(DFI) snowmobiles, personal watercraft, motorcycles and ATV's.
Formulated with wax-free premium quality synthetic esters and a
specialized additive package, INTERCEPTOR is designed to address the
exhaust valve sticking problems associated with certain snowmobile
models.

New AMSOIL HP Injector Synthetic 2-Cycle Oil (HPI), DOMINATOR
Synthetic 2-Cycle Racing Oil (TDR) and Saber Professional (ATP) and
Outboard (ATO) Synthetic 100:1 Pre-Mix 2-Cycle Oils complete the
Fabulous Four lineup, replacing AMSOIL Synthetic 2-Cycle Injector Oil,
Series 2000 Synthetic 2-Cycle Racing Oil and 100:1 Pre-Mix Synthetic
2-Cycle Oil, respectively.