24
CHAPTER 7 INTERNAL ENGINE AND CYLINDER
GENERAL INFORMATION
TC series engines use two cycle operation. Two cycle engines provide a higher horsepower to weight ratio than the
same size four cycle engines. Two cycle engines use two piston strokes for a complete cycle that occurs every crankshaft
revolution, while four cycle engines use four piston strokes and two crankshaft revolutions for a complete cycle.
Lubrication is accomplished through oil mixed in the fuel, and the air / fuel / oil mixture flows into the crankcase during
upward piston travel. This mist lubricates all internal bearing surfaces.
OPERATION
A low pressure area is created in the crankcase as the
piston moves upward to compress the air / fuel mixture in
the cylinder. When the piston moves far enough to uncover
the intake port, the air / fuel mixture from the carburetor
flows into the engine crankcase due to higher pressure
atmospheric air. Just before the piston reaches top dead
center (TDC), the spark plug ignites the air / fuel mixture
in the cylinder.
The expanding combustion gases force the piston down.
The downward piston travel causes a pressure build-up in
the crankcase. The piston uncovers the exhaust port first
followed by the transfer ports. The exhaust flows out the
exhaust port while the pressurized air / fuel mixture enters
the cylinder from the crankcase through the transfer ports.
As the piston travels upward the sequence is repeated
(diag. 7-1).
COMPONENTS
1.
2.
3.
4.
2
3
1
4
5
7-1
7-2
1. CYLINDER
2. "G" CLIP
3. PISTON PIN
4. PISTON
5. ROD
6. CRANKCASE
7. CRANKSHAFT
8. COVER
8
6
7
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