Power Tech (2023) Flashcards
1
Q
What are the 3 Kinds of Horsepower and what do they do?
A
-BHP (Break Horsepower)
Horsepower available at the crankshaft
-IHP (Indicated Horsepower) Developed inside the cylinder
-FHP (Frictional Horsepower) Amount of Horsepower lost to internal friction
2
Q
What is horsepower?
A
The capability of doing a certain amount of work in a specific time
3
Q
What is the calculation for Horsepower?
A
Torque x RPM / 5,252
4
Q
What is Torque?
A
A twisting or turning force
5
Q
What is the calculation for to Torque?
A
Force x Distance (lb x ft)
6
Q
What is force and what is the unit of measure?
A
The pushing of pulling of one object on another (measured in lb)
7
Q
What is work?
A
Force applied through a distance
8
Q
How can 2 different engines produce the same horsepower?
A
RPM and Torque may vary but can amount to the same number
9
Q
When does maximum Torque occur?
A
At Volumetric efficiency (breathing)
10
Q
What is Power?
A
Work over time (work/time)
11
Q
What is the formula for work?
A
Force x Distance
12
Q
What is the difference between Torque and Work?
A
-Torque does not have to move
-Work always has motion involved
13
Q
What is volumetric efficiency?
A
A measure of how well an engine breathes in the air fuel mixture.
14
Q
What is the connecting rod?
A
Attaches piston to crank shaft.
15
Q
How is ‘Bolt size’ measured?
A
Largest diameter of the bolt threads
16
Q
How is ‘Bolt head size’ measured?
A
The dimensions across the flats of the hexagon (same as wrench size)
17
Q
How is ‘Bolt length’ measured?
A
The distance from the base of the bolt head to the threaded end of the bolt
18
Q
How is ‘thread pitch’ measured?
A
US -The number of threads per inch
Metric - Distance between each thread (always measured in mm)
19
Q
How is ‘Grip Length’ measured?
A
The distance form the base of the bolt head to the thread
20
Q
‘Bolt Grades’ defined as
A
Minimum tensile strength of the bolt
21
Q
SAE Grade 5 bolt markings have how many lines?
A
3
22
Q
SAE Grade 6 bolt markings have how many lines?
A
4
23
Q
SAE Grade 1 and 2 bolt markings have how many lines?
A
none!
24
Q
Metric bolts come in what grades?
A
5D, 8G, 10K & 12K (each length and grade combination will vary, see chart)
25
What does UNC stand for?
Unified National Course
26
What does UNF stand for?
Unified National Fine
27
How are Imperial (US) thread types measured?
The number of threads per inch (TPI) of length on threaded fasteners
28
How is Metric thread types measured?
Metric thread pitch is the distance between the threads (can be course or fine)
29
What is the procedure for tapping a hole?
Prior to tapping have new hole drilled with correct diameter
Proper diameter can be found from UNC and UNF threads from a tap drill chart
Use a good tapping fluid (except when tapping gray cast iron, this should be tapped dry)
For through hole, start and end with a taper tap, followed with a plug tap, followed with a bottom tap
Be careful to start the tap straight in the hole
2/3 turn forwards, 1/3 back
Should hear little metal scrapings being taken off when doing 1/3 turn back
Formula for drill size (UNF and UNF) = drills size = basic major diameter – (1.08253 X %) size / no. threads per inch
30
What is the procedure for installing a Helicoil?
Drill and tap hole using appropriate kit
Lubricate new threads
Insert coil until top is slightly below surface of stock
If coil is protruding, pull producing portion away from stock, reach in with a small three corner file, nick the coil (halfway), snap off the tail and file smooth
Test if new threads fit with a bolt
31
What is a stud bolt?
A bolt with one end threaded into a fixture (ex. engine block)
32
Explain Class 1 fit
Has the largest manufacturing tolerance (is used where ease of assembly is required)
33
Explain Class 2 fit
Used on the largest percentage of threaded fasteners (most common)
34
Explain Class 3 fit
Will be tight when assembled
35
How to use a torque wrench? (3 types)
-Click style wrench - set torque value and stop when when wrench clicks
-Dial type torque wrench - watch the needle on the dial and stop at desired torque
-Electric type - set torque value and stop when indicated (ex. flashing or beeping)
36
What is the procedure for torquing a fastener?
Turn the fastener into the material by hand until the head touches the material.
Set torque wrench to appropriate value, apply force until indicated (click, dial or electric types may vary)
37
How do lock washers work?
Lock washers exert a spring tension that locks the fastener and prevents vibration
38
What causes pre ignition?
Preset timing mark caused by:
-Hot spots in the combustion chamber
-Advance timing
-Too hot spark plug
-Low Octane Fuel (wrong type)
-Lean air fuel mixture (not enough fuel)
-Too high compression (valves too tight)
-Insufficient engine cooling
39
What causes detonation? (bad)
Can be caused by:
-Pre-ignition (Hot spots in the combustion chamber allow air fuel mixture to pre ignite (bad), when the connecting rods are pushing the piston up at the same time air fuel mixture is combusting to push piston down, causing piston to rattle with two forces in opposing direction)
(WHICH: is sparks plug worst enemy, as the intense heat and shock wave of the piston rattling damages the sparkplug)
40
What is scavenging?
The Exhaust valve remains open during the first part of the intake stroke (to let out extra exhaust).
The escaping gasses creates a temporary low pressure in the combustion chamber.
(Valve overlap occurs to allow for scavenging to take place)
41
What is valve overlap?
Both Intake and Exhaust valves remain open at the same time (improving volumetric efficiency)
(Valve overlap occurs to allow for scavenging to take place)
42
What are some advantages and disadvantages to overhead camshaft design?
Advantages:
-Higher RPM
-Less lash (Piston in chamber)
-More cooling available
-Reduced cylinder warp
-Lower Friction
-Longer Oil Change intervals
-Reduced wear
-Quieter
Disadvantages:
-More difficult to provide lubrication (parts are moving faster)
-Valve servicing is more complicated
43
Define 'Camshaft throw'
-Engine with large crankshaft “throws” have long strokes
-Longer period is available to charge the cylinder
44
What are the 4 engine head configurations
-L head = both valves open on one side of cylinder
(standard design)
-I head (OHV, Overhead Valve) = valves are inverted above the cylinder (like in Honda from class)
-F head and T head = obsolete designs, first having one valve beside and one above while the latter has one valve on each side of the cylinder (super mf old)
45
The power developed by an engine is controlled by the amount of ______ allowed to enter the manifold
AIR
46
What is the job of the carburetor?
-VAPORIZATION Mixes fuel with the air into air/fuel mixture
-ATOMIZATION to break the fuel into small droplets
-Rapid motion and turbulence are required to keep gasoline molecules suspend in the air
47
Define Stoichiometric balance
14.7 parts air to 1 part fuel
(James said this WILL be on the final)
48
Name and Define the 3 Carburetor types
-Side (or natural) draft - Used when there is little space on top of engine - air flows horizontally into the manifold (Honda from class)
-Up draft - Placed low on engine, gravity fed on fuel, air fuel mixture is forced upward by differential air pressure. Passages are smaller than other carb types
-Down draft - downward flowing air passages aided by gravity, passages are larger.
49
What is the name for Air Fuel Mixture?
Stochiometric Balance
50
What is the narrowed portion of a carburetor?
Venturi vacuum
51
Define Manifold Vacuum
It is a partial vacuum created when the piston travels down in the cylinder with the intake valve open. The only path for air molecules into this area of reduced pressure is via the carburetor.
52
REMINDER (CARB)
REVIEW CARB DIAGRAM
(Find in James' Slides on D2Learning hub Week 4: "#4 Basic Carburation and basic systems theory", Pg 3)
53
What are the modes of operation of the carburetor?
-Idle
-Off Idle
-High Speed (WOT, Wide open Throttle)
-Choke
54
Where is the Power Tech Exam taking place?
RM 117 SW09 (across from the water fountain)
Monday, Dec 11th 2023, 9am
55
What is taking place in the carb when in 'Idle' stage?
-Throttle Plate is nearly closed
-Choke plate fully open
-Small amount of air being drawn through carb
-Fuel is forced through the idle passage and enters the manifold to the right of the throttle plate
-Idle air bleed allows some air to enter idle passage (which creates turbulence to begin (ATOMIZATION)
56
What is taking place in the carb when in 'Off-Idle' stage?
-Additional fuel travels through Fuel passage to increase RPM and power (this is a transitional condition as the engine revs up)
57
What is taking place in the carb when in 'High Speed' stage? (WOT, Wide open throttle)
-Throttle Plate aligned with the carb tube upstream of the venturi
-Main discharge jet allows maximum volume of air-fuel mixture into the manifold
-Vacuum is greatest at this point
-On most small engines a linkage connects throttle plate arm to governer that prevents over-revving (Honda in class)
58
What is taking place in the carb when in 'Choke' stage?
-The choke plate is closed
-Creates low pressure through carb providing a rich mixture
59
What does a 'primer' do in place of a 'choke' stage?
-A small rubber bubble forces pressure into the float bowl
-This has the effect of forcing additional fuel through the discharge tube providing a rich fuel mixture
60
How does a 'gravity-fed' system work?
-Fuel tank is above the carb
-Fuel flow into float bowl is controlled by float valve and seat assembly
61
What is the function of the float?
To maintain a constant level of fuel in the bowl so that the main discharge tube is always drawing fuel from the same level.
62
How does a 'suction feed' system work?
-A diaphragm is connected by passages to the crankcase
-Typically found in machines such as chain saws where the angle operation can change
63
What is the purpose of the governor assembly?
Controls the speed of the engine by moving the throttle and keeps the engine from overheating
64
What controls the flow of gasoline into the float bowl?
Needle and Float
65
Why is an idle circuit needed in addition to the main fuel supply?
To supply the air/fuel mixture into the combustion chamber by bypassing the venturi and coming straight from the float bowl for a richer air/fuel mixture
66
What is the function of the main jet?
Supplies the fuel that mixes with air and keeps the nozzle in place
67
What is the function of the nozzle?
To mix the air and fuel in the nozzle before the venturi
68
What is the anatomy of the 'primary' circuit?
-Battery
-Ignition switch
-Primary winding of the coil
-Breaker points
-Condenser
69
What is the anatomy of the 'secondary' circuit?
-High-tension lead
-Secondary winding of the coil
-Spark Plug
70
How is electrical induction generated in a small engine ignition system?
The induced current is created when magnets (integrated into the flywheel) travel passed a fixed coil, which induces primary voltage.
71
What is Lenz's law?
When a magnet is in motion near a conducting loop, a current is induced in the coil.
-The induced current produced its own magnetic flux opposite in direction to the flux to the moving magnet.
72
What does the term magneto refer to?
Villain in X-men obvi
-Any number of designs that incorporate permanent magnets and a soft iron core wrapped in wire.
73
How many windings are typically in the primary and secondary coils?
Primary Coil (160)
Secondary Coil (10,000)
74
What is the job of the condenser? (also called Capacitor)
-Absorbs current momentarily to prevent arcing in the breaker points.
-Sizing of the capacitor is critical, if too small it would allow arcing
75
How much voltage is created in the primary winding vs the secondary winding?
Primary ~170 Volts
Secondary ~15,000-20,000 Volts
(approx)
76
Why does the secondary winding need to create so much voltage?
The large voltage has to be sufficient enough to overcome the high resistance of the spark plug gap
77
What determines the amount of voltage induced in the secondary circuit?
-The strength of the magnetic field through the iron core (the closer to the magnets are to the core, the greater the magnetic field)
-Speed at which the magnetic field reverses (a fast-spinning magnet
creates a stronger reversing field)
-The number of turns around the iron core
-The amount of voltage needed to jump the spark plug gap (smaller spark plug gap = lower voltage needed)
78
What are the advantages of a magneto ignition system?
-Not dependant on outside source of electricity (ex. battery)
-At higher speeds, magnetic field is stronger, providing a stronger spark
79
What are the functions of the breaker points?
-Controls primary current to the coil
(when points are closed, the magnetic field created by the flywheel magnets is cut by primary coil winding.)
-When the Breaker points are open, current flow in the primary circuit stops and the magnetic field collapses (when the field collapses the high voltage is produced in the secondary winding)
80
What is the purpose of the flywheel magnets?
-They produce strong magnetic fields. (they spin next to the ignition coil and induce current)
-Also acts as failsafe for the engine. This shears off, say when a lawnmower blade gets stuck, so as not to damage the engine
(commonly Alnico magnets, Aluminum, nickel and cobalt)
81
REMINDER (IGNITION)
Review the Ignition diagram!
(Find in James' Slides on D2Learning hub Week 5: "Basic ignition system theory", Pg 1)
82
What is the function of the flywheel key?
Used to position the flywheel on the crankshaft such that the breaker points open at precisely the same time the induced voltage is at its highest
83
List the basic parts of the magneto system
-Permanent magnets
-High-tension coil
-Mechanical or electronic switch
-Condensor (only with mechanical switch)
-High tension spark plug wire
-Spark Plug
84
What does a solid-state system include? (if not using magneto system)
-Electrical source (battery)
-Electronic devices (transistors capacitors, diodes)
(Your actual car, larger engines etc)
85
The ignition coil in a magneto system operates as a _______
Transformer
(not robots in disguise, like the boxes on the side of the road!)
86
What can you use instead of a mechanical breaker point?
An electronic switch
(this is more dependable and there are no breaker points to wear out)
87
What is dwell?
The time at which the breaker points close during one revolution of the cam.
(also known as cam angle)
88
The ignition switch is open =
No spark across the gap of the spark plug when the switch is at the "STOP" position.
(the circuit is open and no longer allowing electricity to flow)
89
What is Coil Saturation?
Describes the condition of the maximum magnetization in an ignition coil
90
What is Spark Advance?
The number of degrees of crank shaft rotation before spark plug is fired
91
What is Spark Retard?
Refers to the condition where spark timing is delayed
92
What is the function of stator laminations?
Convert the rotating magnetic fields into electrical current
93
What is the function of the breaker points?
Open and Close the primary circuit at the correct time
94
What is the function of the secondary (high tension) lead?
Carries high voltage electricity from the secondary winding of the coil to the spark plug
95
What is the function of the spark plug?
Supplies the spark that ignites the air/fuel mixture
96
What MECHANICAL event causes a spark plug to fire?
The magnet spins, creating a magnetic field then the stator laminations turn I into an electrical current, and the secondary lead brings the current to the spark plug
97
When should the spark plug fire?
Right before the piston reaches TDC in the power stroke.
98
What would happen if the breaker points never opened or never closed?
Nothing - the system would be open and nothing would happen - no spark
99
What are 3 methods of disabling the ignition to shut off an engine?
1) Open the switch in the circuit (on-off switch)
2) Unplug the secondary lead
3) Unplug the ignition coil
100
What happens if the spark plug gap is too big or too small?
Too big:
Inconsistently jump between electrodes (run rough or not run at all)
Too small:
spark will be too weak to cause the engine to run
