The two stroke cycle spark ignition engine is a reciprocating engine in which the piston takes over any valve functions in order to obtain a power stroke each revolution of the crankshaft. This involves the use of ports in the cylinder walls which are covered and uncovered by the movements of the piston. As the piston moves down, it clears these ports so that the exhaust gasses can exit and fresh charge of mixture can enter at the same time.

In a typical two-stroke engine the air-fuel mixture enters the crankcase through a reed valve. When the piston is near the bottom of the cylinder a port is uncovered. As prior movement of the piston has compressed the mixture in the crankcase, it flows into the cylinder. Further compression in the cylinder starts as soon as the piston reverses and covers the ports. At the same time compression is occurring in the cylinder, movement of the piston has created a vacuum in the crankcase which draws a fresh charge of mixture from the carburetor into the crankcase. The compressed charge is fired as the piston reaches top dead center. As the expansion of the burning charge forces the piston downward, the reed valve in the crankcase closes and the mixture in the crankcase is compressed. As the piston uncovers the ports at the bottom of the stroke, compressed mixture from the crankcase enters the cylinder again. This incoming fresh mixture then assists in pushing the burned gasses out of the cylinder and the cycle is repeated.

 8-2007

 

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Yummie Yami - Yamaha YFS200/DT200 Blaster

Upgrade The YFS; To Be The Best - Details - 5/27/2003

MacDizzy's Two Stroke Technology Exchange - Message Board

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The Thread Spread - Tech Talk - Details
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Basic Porting - What To Cut - Details	Inside The Glamis Beach Store - Details
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Engine Building Formulas - Details	A TRX250R on the Dyno - Details
A 270 cc TRX Engine - Details	A 370 cc Long Rod Banshee Engine - Details
1990 LT250R Quad Racer Melt Down - Details	Old Friend - The best things in life, free ? Details
TRX Internal Discoveries - Details	Spring 2K - Beach Sand On Demand - Details
Little L Tease - More Power. Please! Details	TRX250R Compression / Compression Ratio Chart - Details
YFSYZ - Been There, Done That ?!? Not This! - Details - Be sure to read the accompanying article that spawned this Blaster pictorial update.

Cylinder Mapping - Primer
Part 1 - Making A Port Map	Part 4 - Finding Top Dead Center (TDC)
Part 2 - Measuring The Ports Correctly	Part 5 - What To Do With The Data
Part 3 - Putting It On Paper	Part 6 - A New Angle

1989 Blaster Engine Rebuild Part 1 - Getting Started Part 8 - Cutting Part 2 - Exposure Part 9 - Evaluation Of Changes Part 3 - Damage & Discrepancies Part 10 - Refinement Part 4 - Cases & Assembly Part 11 - End Gap Part 5 - The Next Phase Part 12 - Flat Top Part 6 - Tools Part 13 - Leak Down Part 7 - More Preparation Part 14 - Running

Two-Stroke Software Review Part 1 - Initial Impressions Bimotion v 2.1 - Blair S.A.E. - Dynomation 2 - MOTA v 5.0 - TSR Bimotion Is Now Freeware - Details

Two Stroke Engine Calculator This Excel spreadsheet was made by an enthusiast. Give it a try - It is password free and worth taking a long look at.
Click here for the Macintosh version - stuffed	Click here for the Windoz version - zipped

More two stroke links - Here.