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Internal Combustion Engine Theory/Operation & Basics

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What is combustion?
The act of process of burning
What gas is compressed, does the temperature of the gas increase or decrease?
increases
What change in motion is accomplished by a crankshaft and connecting rod?
Reciprocating to rotary
What are the 3 factors upon which all ICE rely?
Fuel, air, and ignition
What is a stroke?
Each movement of a piston from top to bottom or from bottom to top
How many stroke does a piston take as a crankshaft makes 1 complete revolution?
2
What is BTC (bottom Dead center)?
The position of a piston at the very instant that its motion changes from down to up
What is another term used for BDC and TDC positions?
Rock positions
What are the 4 strokes in a 4-stroke engine?
Intake, compression, power, exhaust
What is the typical compression ratio in a gasoline engine?
8 to 1
What is the normal pressure rise during the power stroke?
600 to 700 psi
What are the 2 strokes called in the 2-stroke engine?
Compression and power-assisted
Does 1 cycle=1 crankshaft revolution and 2 piston strokes in a 2-stroke engine?
Yes, and a blower is required
Why are many of the parts of a diesel engine somewhat heavier and stronger than compared to parts of a gasoline engine?
Because they must withstand higher pressures and temperatures
Does a diesel engine have a carburetor or spark plugs?
No
What is the order of cylinder firing in a 4-stroke, 6-cylinder engine?
1-5-3-6-2-4
What are the 4 basic types of engine cylinder arrangements?
In-line, V-type, horizontal opposed, and radial
What cylinder arrangement type is most useful when height must be a consideration?
Horizontal opposed
Where is the cylinder firing order of an engine usually indicated?
Stamped on the cylinder block, or on the manufacturer's name plate
In which type of valve arrangement are the intake and exhaust valves both mounted in a cylinder head directly above the cylinder?
I-head configuration
What is the general description of the T-head valve arrangement?
Intake and exhaust valves are positioned on opposite sides of the cylinder in the engine block, and each required their own camshaft
In a double-overhead camshaft configuration, do the intake and exhaust valves each operate from separate camshaft directly through the lifters?
Yes
What is the unit of measurement for work?
Ft-lb
What is the work capacity of a engine measured in?
Horsepower (hp)
What device is used to measure the horsepower of an engine?
Dynamometer
What device employs a flywheel to measure actual usable horsepower?
The Prony brake
What is torque?
The force that tends to result in twisting of an object when applied
What is the unit of measurement of torque?
Lb-ft
What term is used for the rating of the turning force at the engine crankshaft?
Engine torque
What is the power required to overcome engine friction?
Frictional horsepower (fhp)
What is volumetric efficiency?
The ratio between the amount of air-fuel mixture which actually enters a cylinder and the amount which could enter under perfectly ideal conditions
What is the relationship called between the actually power produced in the engine and the actual power delivered at the crankshaft?
Mechanical efficiency
What does the thermal efficiency of an engine indicate?
The relationship between the actual heat energy that is stored within the available fuel and the power that is produced in the engine
What term is used for the inside diameter of an engine cylinder?
Bore
What term is used for the distance between the TDC and the BDC of an engine cylinder?
Stroke
What is the total displacement of an engine?
The volume of 1 cylinder times the total number of cylinders in cubic inches (or liters)
How is the compression ratio determined?
By dividing the volume of 1 cylinder with the piston at the BDC position, by the volume with the piston at TDC
What is the normal air-fuel ratio for a gasoline engine operating at intermediate speeds?
15 lb of air to 1 lb of gasoline
What is the single most important factor which determines how an engine is tailored for special needs?
Valve timing
What are the principal timing points used to measure valve operation in relation to crankshaft position?
The points when the valves open, how long they remain open, and when they close
What is ignition timing?
The timing of the spark plug firing in relation to the piston position during the compression and power stroke
When must be spark be timed to occur?
Before the piston reached TDC on the compression stroke
What are the principles stationary parts of an engine?
Cylinder block, cylinders, cylinder heads, and the exhaust and intake manifolds
What is the best general material for cylinder blocks?
An iron alloy containing nickel and molybdenum
Which material is more expensive, aluminum or cast iron?
Aluminum
What is the maximum diameter variation allowed for a cylinder?
No more than 0.0005 inch (0.12 mm)
What material is used to construction air-cooled engine cylinders?
Forged steel
What devices are used in liquid-cooled engines to provide waring surfaces for the pistons to ride against?
Cylinder sleeves or liners
What are the 2 types of cylinder sleeves?
The dry-type and wet-type
Which type of cylinder sleeve comes into direct contact with the coolant?
Wet
What are the 2 most frequent types of cylinder sleeve casualties?
Cranks and scoring (both require sleeve replacement)
What are the 2 types of core hole plugs used to seal the core holes machined into a cylinder block?
Cup and disk
What is the oil pan of an engine crankcase generally made from?
Cast aluminum or pressed steel
What is the critical role which the oil plan plays in a air-cooled engine?
The elimination of waste heat form the engine through its lubricating oil
Where is the cylinder head bolted in a liquid-cooled engine?
To the top of the cylinder
How much faster than cast iron does aluminum conduct heat?
Approximately 3 times as fast
How large must the water jackets generally be manufactured in an I-head (overhead valve) type of cylinder head?
Sufficiently large enough to cool the top of the combustion chamber, as well as the valves, valve seats, and valve operating mechanisms
What is employed on liquid-cooled engines in order to seal the cylinder heads?
A head gasket
How is a head gasket usually constructed? - As 2 sheets of soft steel which sandwich a layer of asbestos
What device on a gasoline engine is designed to carry the air-fuel mixture from the carburetor and distribute it equally to the cylinder?
The intake manifold
What are intake manifolds designed with smooth walls and few bends that collect fuel?
To reduce condensation of the misture
How can intake manifolds be designed in order to provide for optimal performance for a given speed range?
By varying the length of the manifold passages
What are oil pan gaskets usally made from?
Pressed cork
Can gaskets be constructed by using a silicone sealant?
Yes, by applying the sealant from a squeeze tube to the mating surfaces and letting dry
What is the most commonly used type of oil seal?
Synthetic rubber seal
What is used to hold the rubber element around the shaft in a synthetic rubber seal?
A coil spring
What is another term used for a coil spring?
A garter spring

What are wick seals made of? - Graphite-impregnated asbestos
What type of finish is used on the rotating shaft of a wick seal?
A knurl finish
What are pistons usually made of?
Aluminum alloys
How many times per second (approximately) does a piston move from TDC to BDC of the cylinder in a gasoline engine at normal highway speed?
80
How fast is the piston moving at the mid-point of the stroke?
50 mph
What is another term for the piston pin in a diesel piston assembly?
Wrist pin
Why is the crown a piston machined to a diameter of approximately 0.03 to 0.04 of an inch smaller than the skirt area?
To allow for thermal expansion at the top
What is a T-slot piston?
A split-skirt piston with an added horizontal slot to retard heat transfer from the head of the piston to the skirt
What is a cam-ground piston?
A piston having an elliptical cross-section
What are the 2 main types of piston skirts?
Full trunk, and partial skirt (or slipper)
What is the best type of piston pin to use in order to provide for sufficient hardness, yet not to be too brittle?
A case-hardened steel pin is best
What are the 3 main types of piston pins?
Anchored (fixed), semifloating, and full-floating
What is the most common piston ring configuration?
3-ring piston, which has 2 compression rights from the top, followed by 1 oil control ring
What type of piston ring configuration is commonly used on diesel engines?
4-ring piston having 3 compression rings from the top, followed by 1 oil control ring
What term is used for the additional groove which is cut into the piston just above the top ring groove?
The head dam
What is the purpose of the heat dam?
To divert some of the extreme heat absorbed by the piston head away from the top ring
What is the ring gap?
The split in the piston ring, which is necessary in order to install the ring onto the piston and to allow for expansion from heating
What are the main types of ring gap variations?
Butted gap, beveled gap, lapped gap, and pinned gap
What types of materials are used to coat new piston rings in order to prevent scuffing?
Graphite, phosphate, molybdenum, or some other porous material
What connecting rod design yields the highest general strength and lowest weight?
The I-beam design
What are connecting rods made of?
Forged steel (aluminum in small engine)
What is a precision type of split bearing?
A bearing which is accurately finished to fit a crankpin and requires to further fitting during installation, unlike a semiprecision type of bearing.
What are crankshaft manufactured from?
Either forged steel (commercial and military engines) or cast steel (light-duty and regular-duty gasoline engines)
How far are throws 1 and 4 offset from throws 2 and 3 in and in-line four-cylinder engine?
180 degrees
How many cylinders operate off each throw in a V-type engine?
2 cylinders
How far are the 2 planes offset in a V-type engine (i.e. the plane of the 2 end throw, and the plane of the 2 center throws)?
90 degrees from each other
How far apart are the 3 planes of an in-line six-cylinder engine?
120 degrees
How are crankshaft bearings manufactured?
As precision inserts consisting of a hard shell of steel or bronze with a thin lining of antifrictional metal or bearing alloy.
How can vibration due to deflection be minimized in a crankshaft?
By means of heavy crankshaft construction and by sufficient support along its length by bearings.
What device is used to control torsional vibration?
A vibration damper
What is the purpose of the ring gear on the outer edge of the flywheel?
It is engages the drive gear on the starter motor for cranking the engine
Where is the camshaft located in L-, F-, or I-head engines?
To 1 side and above the crankshaft
Where is the camshaft located in V-type engines?
Directly above the crankshaft
What are camshaft bearing journals , which support the camshafts in the engine block generally made of?
They are bronze bushings, rather than split bearings, and are lubricated by oil which cicurlates through drilled passages from the crankcase.
What are other terms used for camshaft followers?
Valve Tappets or valve lifters
What are the 2 basic kinds of camshaft followers?
Mechanical (or solid) tappets, and hydraulic tappets
What designs are used for the intake and exhaust valves in a 4-stroke-cycle engine?
The valves are of the poppet design and are manufactured in 3 basic shapes: tulip, semitulip, an mushroom, depending upon the shape and requirements of the combustion chamber
What are intake valves made from?
Nickel chromium alloy
What are exhaust valves made from?
Silichrome alloy
What condition causes valve float to occur?
Low-spring tension (the valve spring is too weeak to close the valve at high engine rpm
What is the purpose of a valve seal?
Valve seals, which may be either of the umbrella or the O-ring type, prevent valve operating mechanism oil from running down the valve stem into the combustion chamber
What is the function of a valve rotator?
Turns the valve in order to prevent any carbon buildup or hot spots on the valve face
What is the normal interference angle setting on a valve grinding machine chuck assembly?
There is normally a 1 degree difference in valve face angle and valve seat angle
Why must a face shield always be worn when grinding valves?
Because the stone could shatter, and debris could be thrown into the operator's face
What condition is indicated if a valve wobbles as it is turning on a valve grinding machine?
The valve is either bent or is incorrectly chuched
What problems are caused by excessive wear of valve guides?
Valve guide causes a valve to move sideways in its guide during operation (causing oil consumption from oil leaks past the valve seal and through the guide), or burned and broken valves
What is a pilot, used in valve seating?
It is a metal shaft which fits into the guide and supports the cutting stone or carbide cutter.
What is the normal valve-to-seat contact width for an exhaust valve?
About 3/32nd of an inch
What are the 3 basic characteristics of valve springs which should be checked during engine servicing?
1. Valve spring squareness, 2. Valve spring free height, 3. Valve spring tension
What are the marks called which are used to designate the initial position between the crankshaft and the camshaft?
Timing marks
What are the 3 types of gear trains used to achieved correct gear timing?
1. Gear-drive, 2. Chain-drive, 3. Belt-drive
What is the purpose of the tensioner on a belt-drive gear train?
To push against the belt and keep it tight, so that the chain does not slip on the sprockets, thus providing for more precise valve timing.
Is the following a true statement: The greater the oil clearance, the faster the oil flows through the bearings?
Yes
What is bearing load strength?
The capability of a bearing to withstand pounding and crushing during engine operation.
What is bearing embedability?
The capability of a bearing to shift, conform, or move to variations in the shaft alignment, and to adjust to any imperfection in the journal surface.
What 3 basic types of metal alloys are employed as plating over the backing material for engine bearings?
Babbit (lead-tin alloy): copper; and aluminum or different combinations of the 3 alloys
What are the principal conditions which can cause low engine compression?
A burned valve or burned valve-seat, a blown head gasket, physical engine damage, worn cylinders or rings, valve train problems, or a jumped timing chain or belt-drive
What should the feed wire to the ignition coil be removed to disable the ignition system prior to performing an engine compression test?
To prevent any sparks from arcing out of the disconnected spark plug wires.
Why should all spark plugs be removed before a compression test?
So that the engine can freely rotate
How high should a diesel gauge be able to read for a diesel engine compression test?
Up to approximately 600 psi
Why is it important to not place too much oil into a cylinder during a wet compression test of a diesel engine?
Because a false reading could result, due to the fact that compression readings would go up even if the compression rings and cylinders are in proper condition.
What are average compression readings for gasoline engines?
About 125 to 175 psi
What are average compression readings for diesel engine?
About 275 to 400 psi
Which vacuum readings can be tested by using a vacuum gauge?
1. Intake manifold, 2. Cranking 3. Fuel pump, 4. Booster pump
How much should the average vacuum gauge reading drop for every 1,000 ft of altitude about sea level?
~1 inch per 1,000 feet
What condition is indicated by a loud air hissing sound at the oil filler tube (crankcase) during a cylinder leakage test?
An excessive air leak past the piston rings