2 &
4 Stroke Engine Principles
The Basic Difference
The main difference between 2 & 4 stroke engines is
the way they use oil. As any 2 metal surfaces rub together
(such as the piston & piston rings rubbing up &
down against the cylinder barrel), friction is caused. This
friction causes the metal parts to wear as they rub against
each other. In order to minimise friction & wear on
engine components, engines use oil as lubrication which
provides a thin layer of protection between the metal surfaces.
2 Stroke Engines: In a 2 stroke engine,
the fuel & air is mixed with 2 stroke oil, either pre
mixed in the petrol tank or added automatically from a separate
oil reservoir, the oil in the fuel & air mixture lubricates
the cylinder, piston & piston rings, crankshaft &
components. The 2 stroke oil is burnt with the fuel &
air in the cylinder which produces a bluish tinge to the
exhaust gases as well as that unique 2 stroke smell.
4 Stroke Engines: 4 stroke engines use
an oil sump to lubricate the internal moving components
of a motorcycle engine, which means there isn't any need
to mix oil with the fuel & air mixture. This generally
produces better fuel economy & cleaner exhaust emissions.
4 stroke engines transport the oil around the engine from
the oil sump (located at the bottom of a 4 stroke engine,
the sump is a reservoir for the engine oil) to the moving
engine parts using a series of passages in the engine casings
& grooves, the oil is usually driven round the engine
by an oil pump. 4 stroke engines use a 'recirculating oil
system', which means the oil is driven, from the sump, by
the oil pump, through an oil filter, around the engine &
back to the sump to be used again.
Please click on either the 2 or 4
stroke links below to proceed
The links below are to pages that explain the basic operating
principles of 2 & 4 stroke motorcycle engines
2
Stroke Engines
4
Stroke Engines
Pros
& Cons of 2 & 4 Stroke Engines
2 Stroke Engines
Pros |
Cons |
Simple to produce |
High noise levels |
Easy & cheap to manufacture |
High Pollution levels (caused by
burning of oil with the fuel) |
Relatively high power output for
CC |
Low fuel economy |
Ideal for smaller motorcycles &
scooters up to 125cc due to low production cost &
good power output |
Narrow power band |
|
Due to the way oil is burnt in the
cylinder, re-bores are required every so often |
4 Stroke Engines
Pros |
Cons |
More even power spread across the
rev range |
More complicated to produce than
a 2 stroke engine |
Good fuel economy |
High manufacturing costs due to
more complex design |
Lower levels of exhaust emissions |
|
More efficient engine system |
|
Please note:
As a general rule,
due to lower manufacturing costs
& simplicity of design, 2 stroke engines have been commonly
used in motorcycles & scooters up to 125cc, motorbikes
& scooters over 125cc have tended to be mainly 4 stroke.
But, as technology has advanced, most of the problems associated
with either 2 or 4 stroke engines have been or are being engineered
out.So, although smaller engines still tend to be 2 stroke
& larger motorcycle engines tend to be 4 stroke, engines
have remained this way due to manufacturing costs rather then
because of limits in design or engineering technology.
|
