question about 4 strok

[reanimation]

hi, i know that 2 stroke engine uses 2 t to lubricate the block, i am juz wondering for 4 stroke what does it uses to lubricate the block and piston.. thanks in advance...

[Blahhh]

Engine oil

[natgw]

2stroke - 2t

 

4stroke - _t

 

pls fill in the blank urself.

[scoobydoo]

4T

In a typical 4-stroke engine, 4T lubricates the crankshaft bearings, bearings on piston's conn-rod, cylinder wall, piston rings, etc. Thus, if the engine's piston rings are worn our and loose, we see white smoke coming out from the exhaust. This is because too much 4T enters the combustion chamber and gets burnt off together with the fuel/air mixture.

2T

In a two-stroke engine, 2T is mixed with fuel/air to lubricate the crankshaft, conn-rod, cylinder walls, piston rings, etc. 4T cannot be used because the crankcase serves as a pressurization chamber to force fuel/air/2T mixture into the cylinder, it cannot hold thick oils like 4T.

 

these posts below help us understand how 2 stroke and 4 stroke engines work

 

2 stroke engines have pretty different construction as 4 stroke ones. Typically engines (e.g. TA150) don't have valves to take in fule/air or let out exhaust. Modern engines employ power valve systems and have valves in or around the exhaust ports to get better low end power without losing high rpm power.

E.g. Yamaha YPVS... alter the exhaust port by closing off the top part of the port which alters port timing

E.g. Honda V-TACS... altering the volume of the exhaust which changes the resonant frequency of the expansion chamber

 

http://upload.wikimedia.org/wikipedia/commons/5/52/Arbeitsweise_Zweitakt.gif

 

The typical 2 strokes are:

 

1. Power/exhaust:

Spark initiated combustion, piston is forced down. When piston moves down till its top passes the exhaust port, most of the pressurized exhaust gases escape through the port. As piston continue to move down, it prepares for intake by compressing the fuel/air/2T mixture in crankcase. When top of piston pass the transfer port, the compressed fuel/air/2T mixture enters the cylinder from the crankcase and pushes out the remaining exhaust.

 

http://static.howstuffworks.com/gif/two-stroke-exhaust.gif

 

2. Intake/Compression:

After the fuel/air/2T mixture enter the cylinder, piston moves up and start to compresses mixture in the cylinder. This creates a vacuum in the crankcase to pull in the new fule/air/2T from carburetor. Once compression is completed, spark plug ignites the compressed mixture and the cycle goes on.

 

http://static.howstuffworks.com/gif/two-stroke-intake.gif

 

Notice that both ports are open at some time? As fresh fuel/air/2T mixture enters the combustion chamber, part of it also leaks out through the exhaust port.

 

http://static.howstuffworks.com/gif/two-stroke-compress.gif

 

 

The piston is doing 3 things in a two-stroke engine:

a) Top side of piston is the combustion chamber where fuel/air/2T mixture is compresses and burnt to generate power

b) Bottom side of piston is the crankcase where created vacuum suck in fresh fule/air/2T from carburetor through the reed valve. Piston then pressurise the crankcase so that fresh mixture can force its way into the combustion chamber when intake port opens.

c) Sides of the piston act like valves, covering and uncovering the intake and exhaust ports at the side of cylinder wall

 

2T & 4T

In a typical 4-stroke engine, the crankcase is usually separated from the combustion chamber and is filled with 4T to lubricate the crankshaft bearings, bearings on piston's conn-rod, cylinder wall, etc.

In a two-stroke engine, the crankcase serves as a pressurization chamber to force fuel/air/2T mixture into the cylinder, so it can't hold thick oils. 2T is thus required and mixed with fuel/air to lubricate the crankshaft, conn-rod, cylinder walls, etc. If you forget to top up your 2T, excessive wearing will occur and piston may become jammed in the cylinder in a worst case situation.

 

INFO SHARING

 

http://gizmodo.com/gadgets/fourstroke-action/micro-camera-shows-the-workings-of-a-combustion-engine-309138.php

 

 

Engine cycle begins at top dead center (TDC), when the piston is furthest away from the crankshaft. On the intake or induction stroke (known as the first stroke) the piston moves downwards & pressure is reduced in the cylinder. A mixture of fuel and air is forced, by at least atmospheric pressure, into the cylinder through the inlet (known as intake) port. The inlet valve(s) then close(s) and the following upward stroke (compression) compresses the fuel-air mixture.

 

http://upload.wikimedia.org/wikipedia/commons/a/a6/4-Stroke-Engine.gif

 

 

Next the spark plug comes in by igniting the air-fuel mixture, at approximately the top of the compression stroke. Combustion takes place with expansion in gases as part of the by products, which pushes the piston downward for the third stroke (common known as the power stroke). Finally as the piston moces upwards again, it pushes the products of combustion from the cylinder through an exhaust valve or valves. This fourth stroke (exhaust) completes the cycle

 

 

 

cheers