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Therory 1 - Two-Stroke Engine Operation > Two-Stroke Engine Operation > Flashcards

Two-Stroke Engine Operation Flashcards

0
Q

When does scavenging occur in the two-stroke engine?

A

When exhaust and transfer ports are open at the same time.

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1
Q

List the five events of two-stroke engine operation (remember, same as 4 stroke except one extra).

A 
A. Intake 
B. Combustion
C. Compression
D. Exhaust
E. Transfer
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2
Q

What is the purpose of loop scavenging?

A

Minimize loss of the intake charge mixture out of the exhaust port.

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3
Q

what are the three major moving parts of a two-stroke engine?

A

A. Piston
B. Connecting Rod (one piece)
C. Crankshaft (multi-piece)

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4
Q

Name two purposes of the expansion chamber.

A
  1. Aids in scavenging

2. Shapes the engine powerband

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5
Q

When does piston port design intake open?

A
  1. Opens at BTDC

2. Closes at ATDC

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6
Q

When does the piston port design exhaust open and close?

A
  1. Opens at BBDC

2. Closes at ABDC

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7
Q

When does the piston port design transfer open and close?

A

Transfer opens at BBDC

Transfer closes at ABDC

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8
Q

The five events occur in how many strokes of the piston?

A

Two

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9
Q

The five events occur in how many revolutions of the crankshaft?

A

One

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10
Q

Where in the engine does primary compression take place?

A

In the primary area.

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11
Q

Where in the engine does secondary compression take place?

A

In the secondary area.

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12
Q

Name four variations from the basic piston-port intake design.

A
  1. Cylinder Reed Valve
  2. Crank case Reed Valve
  3. Rotary Valve
  4. Piston Port Crankcase reed valve
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13
Q

Which is the most common piston-port intake design?

A

The Cylinder Reed Valve.

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14
Q

What is the essential purpose of these variations from the basic piston-port intake design?

A

To make intake time asymmetrical.

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15
Q

Which induction system uses a a disc to control the intake?

A

The Rotary Valve.

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16
Q

What does an “exhaust power valve” do?

A

Alters the exhaust ports type.

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17
Q

What are the three main ports in the two-stroke cylinder, and what are their purposes?

A

A. Exhaust; routes combustion
B. Intake; routes mixture into the primary
C. Transfer; routes mixture from primary to secondary

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18
Q

Port

A
  1. Part of the cylinder

2. Controls the airflow into and out of the engine.

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19
Q

Primary

A

All the area under the piston crown (primary compression occurs here)

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20
Q

Secondary

A

All the area above the piston crown (secondary compression occurs here)

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21
Q

Major areas

A

Primary and Secondary

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22
Q

Intake port

A
  1. Lowest port in the cylinder wall

2. Controlled by Skirt

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23
Q

Exhaust port

A
  1. Controlled by the piston Crown

2. Routes spent gases out of the cylinder

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24
Q

Transfer port

A
  1. Controlled by the piston Crown

2. Transfer mixture from Primary to Secondary

25
Q

Upstroke

A
  1. Intake
  2. Compression
  3. Combustion
26
Q

Downstroke

A

Exhaust and transfer occur

27
Q

Exhaust

A

Longest duration

28
Q

Transfer

A

Shortest duration

29
Q

Symmetrical

A

A. Open and close equal distance from dead center

B. Narrow tuning

30
Q

Scavenge

A
  1. Evacuation of spent gases exhaust gases by force of incoming mixture
  2. Minimize charge loss
31
Q

Loop scavenge

A

Transfer ports angled to minimize loss of charge out the exhaust port

32
Q

Cross scavenge

A

Piston crown designed to minimize loss of charge out the exhaust port

33
Q

Expansion Chamber

A

Shapes engine powerband (sonic waves move up and down the pipe)

34
Q

Piston port design variations

A

Make intake port timing asymmetrical

35
Q

Cylinder Reed Valve

A

A. Most common

B. Widest possible power-band

36
Q

Rotary Valve

A

A. Rotary disc valve on crankshaft end, driven by crankshaft

B. Most tunable

37
Q

Piston port/crankcase reed (combo)

A
  1. Good overall power

2. Parallel passages

38
Q

Power Valves

A

A power valve alters the exhaust port’s height, width, or length.

39
Q

Cylinder head

A

A. Centrally located spark plug and large amount of squish aids combustion.

B. No Valves

40
Q

Types of Cylinder head

A
  1. Cast-iron
  2. Aluminum w/ cast-iron sleeve
  3. Plated Aluminum.
41
Q

Cylinder, Servicing

A
  1. Must be chamfered after boring the cylinder.
  2. Very wide ports are bridged to prevent rings catching on port edges.
  3. Measured 6 x’s X and Y axis, Top, Center, and bottom of cylinder.
42
Q

Crosshatch

A
  1. Seats piston rings

2. Controls cylinder lubrication

43
Q

Piston

A
  1. Cast (common) and Forged (high performance)
  2. Transfers power to connecting rod
  3. Tapered - Crown smaller than skirt
  4. Elliptical - Allows for expansion
44
Q

Piston Ring purpose and Ring types:

A
  1. To seal primary area from secondary area.
    A. Standard: Rectangular cross section.
    B. Keystone: Wedge cross section. Cleans groove.
    C. Dykes: Prevents ring flutter
45
Q

Wrist pin

A

Lubricated by slot or hole in connecting rod

46
Q

Connecting Rod

A
  1. Needle bearings on small end

2. Ball Bearing on Large end

47
Q

Crankshaft

A

Ball main bearings

48
Q

Multi-cylinder crankshafts

A

Labyrinth seal used between cylinders to keep positive and negative pressures from each other

49
Q

Crankcase

A

Wet side seal (clutch): if it leaks engine smokes excessively

Dry Side seal (ignition): if it leaks, engine runs lean and may seize

50
Q

Crankcase

A

Leakdown test

51
Q

How much oil to a gallon?

A

128 / ratio x number of gallons = oz oil.

52
Q

More oil

53
Q

More Fuel

54
Q

What are the eight causes of two-stroke engine seizure?

A

A. Lean B. Tight
C. Lubrication D. Timing (not adjustable)
E. Loading F. Torque
G. E. Temperature

55
Q

An oil injection lubrication system is regulated by which two things?

A

Throttle opening and engine RPM

56
Q

What are two methods of lubricating a two-stroke engine?

A

Pre-mix and oil injection

57
Q

What test is made if you suspect that a two stroke primary is no longer air tight; and what areas of the engine must be sealed before beginning test?

A

Leak down test and the intake and exhaust must be sealed before starting tests.

58
Q

What type of crankshaft is used in a two-stroke engine?

A

Multi-piece

59
Q

What type of case is found in a single-cylinder two-stroke engine?

A

Vertical split

Therory 1 - Two-Stroke Engine Operation (2 decks)

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