week two engines

The intake valve closes 45° of crankshaft rotation after the piston passes bottom dead center, moving upward on the compression stroke. Both valves are closed at this point, and they both remain closed until the piston passes over top center and comes down to 70° before bottom dead center on the power stroke. At this time the exhaust valve opens. Both valves are on their seats for 45° + 180° + 20°, or 245°.

019. Using the following information, determine how many degrees the crankshaft will rotate with both the intake and exhaust valves seated. Intake opens 15° BTDC. Exhaust opens 70° BBDC. Intake closes 45° ABDC. Exhaust closes 10° ATDC. A— 290°. B— 245°. C— 25°.

All of the alternatives except low oil temperature would likely be caused by failed or failing engine bearings in a reciprocating engine. Low oil temperature would be the least likely of these alternatives.

8003. Which condition would be the least likely to be caused by failed or failing engine bearings? A— Excessive oil consumption. B— High oil temperatures. C— Low oil temperatures.

The horsepower produced by a reciprocating engine is determined by its RPM. The higher the RPM, the greater the power. But the efficiency of a propeller decreases as the blade tip speed approaches the speed of sound. In order to get the best of both conditions, many of the more powerful aircraft engines drive the propeller through a set of reduction gears. Reduction gears allow the engine to turn fast enough to develop the required power. At the same time, the propeller tip speed is kept low enough that the tips do not approach the speed of sound.

8004. What is the principal advantage of using propeller reduction gears? A— To enable the propeller RPM to be increased without an accompanying increase in engine RPM. B— To enable the engine RPM to be increased with an accompanying increase in power and allow the propeller to remain at a lower, more efficient RPM. C— To enable the engine RPM to be increased with an accompanying increase in propeller RPM.

The volumetric efficiency of a reciprocating engine is the ratio of the weight of the fuel-air charge taken into the cylinder, to the weight of a charge that would completely f ill the entire volume of the cylinder at the same pressure. Anything that decreases the weight of the air entering the cylinder decreases the volumetric efficiency. Improper valve timing, sharp bends in the induction system, and high carburetor air temperature will all decrease the volumetric efficiency.

8005. Which of the following will decrease volumetric efficiency in a reciprocating engine? 1. Full throttle operation. 2. Low cylinder head temperatures. 3. Improper valve timing. 4. Sharp bends in the induction system. 5. High carburetor air temperatures. A— 2, 4, and 5. B— 1, 2, 3, and 4. C— 3, 4, and 5.

Deep-groove ball bearings are used as the thrust bearing in most radial engines. This type of bearing is the best of those listed for reducing friction while carrying both thrust and radial loads.

8006. Which of the following is a characteristic of a thrust bearing used in most radial engines? A— Tapered roller. B— Double-row ball. C— Deep-groove ball.

the master rod bearing in a radial engine is always a plain bearing. Rocker arm bearings may be either ball, roller, or plain type and the crankshaft main bearings for radial engines are usually ball bearings.

8007. Which bearing is least likely to be a roller or ball bearing? A— Rocker arm bearing (overhead valve engine). B— Master rod bearing (radial engine). C— Crankshaft main bearing (radial engine).

When a radial engine is operating, the cast aluminum alloy cylinder head expands far more than the steel push rod. As the cylinder head expands, the rocker arm moves away from the cam ring and the hot, or running, valve clearance becomes much greater than the cold clearance.

8008. The operating temperature valve clearance of a radial engine as compared to cold valve clearance is A— greater. B— less. C— the same.

The piston displacement of a reciprocating engine is the total volume swept by the pistons in one revolution of the crankshaft. Find the piston displacement of one cylinder by multiplying the area of the piston in square inches by the stroke, which is measured in inches. The total piston displacement is the volume of one cylinder, measured in cubic inches, multiplied by the number of cylinders. rea = 0.7854 × bore 2 = 0.7854 × 30.25 = 23.75 square inches Volume = piston area × stroke = 23.75 × 6 = 142.55 cubic inches Piston displacement = volume × number of cylinders = 142.55 × 9 = 1,282.95 cubic inches

8009. A nine-cylinder engine with a bore of 5.5 inches and a stroke of 6 inches will have a total piston displacement of A— 740 cubic inches. B— 1,425 cubic inches. C— 1,283 cubic inches.

The five events that take place in a reciprocating engine during each cycle of its operation are: Intake — The fuel-air mixture is taken into the cylinder. Compression — The fuel-air mixture is compressed as the piston moves upward (outward) in the cylinder. Ignition — As the piston nears the top of its stroke, an electrical spark ignites the mixture so it burns and releases its energy. Power — As the fuel-air mixture burns, it forces the piston downward. This movement of the piston rotates the crankshaft and performs useful work. Exhaust — After the piston has reached the bottom of its stroke and done the most of its useful work, the piston pushes upward, forcing the burned gases out of the cylinder.

8010. The five events of a four-stroke cycle engine in the order of their occurrence are A— intake, ignition, compression, power, exhaust. B— intake, power, compression, ignition, exhaust. C— intake, compression, ignition, power, exhaust.

he firing order of an opposed engine is designed to provide for balance and to eliminate vibration as much as possible.

8011. The primary concern in establishing the firing order for an opposed engine is to A— provide for balance and eliminate vibration to the greatest extent possible. B— keep power impulses on adjacent cylinders as far apart as possible in order to obtain the greatest mechanical efficiency. C— keep the power impulses on adjacent cylinders as close as possible in order to obtain the greatest mechanical efficiency.

The ignition of the fuel-air mixture in the cylinder of a reciprocating engine is timed so it occurs when the piston is about 20 to 30 degrees of crankshaft rotation before reaching top center on the compression stroke. If the mixture ratio and ignition timing are both correct, the fuel-air mixture will be all burned shortly after the piston passes over top center. The expanding gases caused by absorbing heat from the burning mixture will exert the maximum amount of push on the descending piston during the power stroke.

8012. If fuel/air ratio is proper and ignition timing is correct, the combustion process should be completed A— 20 to 30° before top center at the end of the compression stroke. B— when the exhaust valve opens at the end of the power stroke. C— just after top center at the beginning of the power stroke.

if a valve is ground with a feather edge (a thin edge) the heat in the cylinder will cause the thin area to glow red hot and this will ignite the fuel-air mixture before the correct time for ignition. This will result in preignition and burned valves.

8013. Grinding the valves of a reciprocating engine to a feather edge is likely to result in A— normal operation and long life. B— excessive valve clearance. C— preignition and burned valves

Torsional vibration caused by firing impulses of the engine are minimized by the installation of moveable counterweights suspended from certain crank cheeks. These moveable counterweights, called dynamic dampers, rock back and forth and act as pendulums, changing the resonant frequency of the rotating elements, thus reducing the torsional vibration.

8014. Which statement is correct regarding engine crankshafts? A— Moveable counterweights serve to reduce the dynamic vibrations in an aircraft reciprocating engine. B— Moveable counterweights serve to reduce the torsional vibrations in an aircraft reciprocating engine. C— Moveable counterweights are designed to resonate at the natural frequency of the crankshaft.

Both the intake and exhaust valve are open at the same time only during the period of valve overlap. Valve overlap occurs at the end of the exhaust stroke and the beginning of the intake stroke. The intake valve opens a few degrees of crankshaft rotation before the piston reaches the top of the exhaust stroke. The exhaust valve remains open until the piston has moved down a few degrees of crankshaft rotation on the intake stroke.

8015. On which strokes are both valves on a four-stroke cycle reciprocating aircraft engine open? A— Power and exhaust. B— Intake and compression. C— Exhaust and intake.

Master rods used in radial engines have plain bearings in both their big end that fits around the throw of the crankshaft and the small end that fits around the wrist pin in the piston.

8016. Master rod bearings are generally what type? A— Plain. B— Roller. C— Ball.

The actual horsepower delivered to the propeller of an aircraft engine is called brake horsepower. This name is used because brake horsepower was originally measured with a prony brake loading the engine with mechanical friction. Modern measurements of brake horsepower are made with a dynamometer which loads the engine with electrical or fluid-flow opposition.

8017. The actual power delivered to the propeller of an aircraft engine is called A— friction horsepower. B— brake horsepower. C— indicated horsepower.

A cam-ground piston is one whose diameter is a few thousandths of an inch greater in a plane perpendicular to the wrist pin boss than it is parallel to the boss. When the piston reaches its operating temperature, the large mass of metal in the piston pin boss expands enough that the piston becomes round. Since the piston is round at its operating temperature, it provides a better seal than it would if it were round while cold and expanded to an out-of-round condition when hot.

8018. Cam-ground pistons are installed in some aircraft engines to A— provide a better fit at operating temperatures. B— act as a compensating feature so that a compensated magneto is not required. C— equalize the wear on all pistons.

Some aircraft engine cylinders are ground with the diameter at the top of the barrel, where it screws into the head, slightly smaller than the diameter in the center of the barrel. This is called choke grinding. The large mass of the cylinder head expands more when heated than the smaller mass of the cylinder barrel, so the diameter of a choke-ground cylinder becomes uniform when the engine is at its operating temperature.

8020. Some aircraft engine manufacturers equip their product with choked or taper-ground cylinders in order to A— provide a straight cylinder bore at operating temperatures. B— flex the rings slightly during operation and reduce the possibility of the rings sticking in the grooves. C— increase the compression pressure for starting purposes.

There is no clearance in the valve-operating mechanism when an engine equipped with hydraulic valve lifters is operating normally and the minimum oil and cylinder-head temperatures for takeoff have been reached. Hydraulic valve lifters are used because they remove all of the clearance between the rocker arm and the tip of the valve stem. By keeping all of this clearance removed, the valves operate with less noise and less wear.

8021. An aircraft reciprocating engine using hydraulic valve lifters is observed to have no clearance in its valveoperating mechanism after the minimum inlet oil and cylinder head temperatures for takeoff have been reached. When can this condition be expected? A— During normal operation. B— When the lifters become deflated. C— As a result of carbon and sludge becoming trapped in the lifter and restricting its motion.

A top dead center indicator is used to show when the piston in cylinder number one is on top dead center. A timing disk is clamped to the propeller shaft and positioned so the pointer, which is held straight up by a weight on one end, points to zero degrees. As the crankshaft is rotated, the pointer indicates on the scale of the timing disk the number of degrees the crankshaft has rotated.

8022. What tool is generally used to measure the crankshaft rotation in degrees? A— Dial indicator. B— Timing disk. C— Prop Protractor.

The piston in a reciprocating engine is not moving when it is at the top and bottom of its stroke. As it leaves top dead center, it accelerates from zero velocity to a maximum velocity, which is reached when it is 90° beyond top dead center. It then decelerates to zero velocity at bottom dead center.

8023. If an engine with a stroke of 6 inches is operated at 2,000 RPM, the piston movement within the cylinder will be A— at maximum velocity around TDC. B— constant during the entire 360° of crankshaft travel. C— at maximum velocity 90° after TDC.

The intake valve opens when the piston is moving upward at the end of the exhaust stroke. Opening at this point allows the low pressure caused by the inertia of the exiting exhaust gases to assist in starting the fuel-air mixture f lowing into the cylinder. If the intake valve opens too early, some of the burning exhaust gases could flow into the intake manifold and ignite the mixture. This would cause a backfire in the induction system.

8024. If the intake valve is opened too early in the cycle of operation of a four-stroke cycle engine, it may result in A— improper scavenging of exhaust gases. B— engine kickback. C— backfiring into the induction system.

The walls of an aircraft-engine cylinder are subjected to a great deal of wear as the iron piston rings rub against them. The walls of some cylinders are treated to increase their hardness and resistance to wear. There are two methods of hardening these surfaces: hard-chrome-plating and nitriding. Nitriding is a process in which the surface of the steel cylinder wall is changed into a hard nitride by an infusion of nitrogen from the ammonia gas used in the nitriding heat treatment process.

8025. Some cylinder barrels are hardened by A— nitriding. B— shot peening. C— tempering.

The intake valve in a four-stroke-cycle aircraft engine closes somewhere around 60° after bottom center on the compression stroke. The exhaust valve opens about 70° before bottom center on the power stroke. The intake valve opens about 20° before top center on the exhaust stroke. The exhaust valve closes about 15° after top center on the intake stroke.

8026. Which statement is correct regarding a four-stroke cycle aircraft engine? A— The intake valve closes on the compression stroke. B— The exhaust valve opens on the exhaust stroke. C— The intake valve closes on the intake stroke.

In normal operation, an aircraft engine cylinder wears more at the top than in the center or at the bottom. This greater wear is caused by the heat of combustion decreasing the efficiency of the lubrication at the top of the cylinder.

8027. On which part of the cylinder walls of a normally operating engine will the greatest amount of wear occur? A— Near the center of the cylinder where piston velocity is greatest. B— Near the top of the cylinder. C— Wear is normally evenly distributed.

One recommended way of checking exhaust valves for stretch is by measuring the diameter of the valve stem with a vernier outside micrometer caliper at a point specified by the engine manufacturer. If the valve has stretched, the stem diameter will be smaller than it should be. Another way of determining if a valve has been stretched is by using a valve radius gauge to see if the radius between the valve stem and head is the same radius the valve had when it was manufactured.

8028. During overhaul, reciprocating engine exhaust valves are checked for stretch A— with a suitable inside spring caliper. B— with a contour or radius gauge. C— by placing the valve on a surface plate and measuring its length with a vernier height gauge.

Ignition occurs in a reciprocating engine somewhere around 30° of crankshaft rotation before the piston reaches top center on the compression stroke. By timing the ignition to occur when the piston is in this position, the maximum pressure inside the cylinder is reached just after the piston passes over top center and starts down on the power stroke.

8029. When is the fuel/air mixture ignited in a conventional reciprocating engine? A— When the piston has reached top dead center of the intake stroke. B— Shortly before the piston reaches the top of the compression stroke. C— When the piston reaches top dead center on the compression stroke.

The crankshaft rotates 28° on the compression stroke after the ignition occurs. The crankshaft rotates 180° on the power stroke. The crankshaft rotates 165° on the exhaust stroke before the intake valve opens. The total crankshaft rotation between the time ignition occurs and the time the intake valve opens is: 28° + 180° + 165° = 373°.

8030. Ignition occurs at 28° BTDC on a certain four-stroke cycle engine, and the intake valve opens at 15° BTDC. How many degrees of crankshaft travel after ignition does the intake valve open? (Consider one cylinder only.) A— 707°. B— 373°. C— 347°.

Some aircraft-engine poppet valves have a groove cut in their stem that is fitted with a safety circlet, a small snap ring that grips the valve stem in this groove. If the tip of the valve stem should ever break off in operation, this safety circlet will contact the top of the valve guide and prevent the valve from dropping into the cylinder.

8031. What is the purpose of the safety circlet installed on some valve stems? A— To hold the valve guide in position. B— To hold the valve spring retaining washer in position. C— To prevent valves from falling into the combustion chamber.

Valve overlap is the number of degrees of crankshaft rotation that both the intake and exhaust valves are off their seat at the end of the exhaust stroke and the beginning of the intake stroke. Valve overlap allows a greater charge of fuel-air mixture to be inducted into the cylinder.

8032. Valve overlap is defined as the number of degrees of crankshaft travel A— during which both valves are off their seats. B— between the closing of the intake valve and the opening of the exhaust valve. C— during which both valves are on their seats.

Hydraulic valve lifters are used to keep all of the clearance out of the valve system when the engine is operating and the lifters are pumped up. When the lifters are completely flat, there will be clearance in the system of a specified amount above zero.

8033. The valve clearance of an engine using hydraulic lifters, when the lifters are completely flat, or empty, should not exceed A— 0.00 inch. B— a specified amount above zero. C— a specified amount below zero.

the intake valve closes when the piston is moving upward on the compression stroke. At this time, the exhaust valve is already closed.

8034. If the exhaust valve of a four-stroke cycle engine is closed and the intake valve is just closed, the piston is on the A— intake stroke. B— power stroke. C— compression stroke.

The maximum compression ratio of an engine is limited by the ability of the engine to withstand detonation in its cylinders. Of the alternatives given with this question, three of them are factors affecting the engine's ability to withstand detonation. The detonation characteristics of the fuel used is a limiting factor. Fuels having a low critical pressure and temperature must not be used with high compression engines. The design limitations of the engine are important, because engines that are not designed strong enough to withstand high cylinder pressures, must not have a high compression ratio. The degree of supercharging is extremely important, because the cylinder pressures are a function of both the initial pressure in the cylinder (the pressure caused by the supercharger) and the compression ratio. The only alternative that does not limit the compression ratio is the spark plug reach.

8035. How many of the following are factors in establishing the maximum compression ratio limitations of an aircraft engine? 1. Detonation characteristics of the fuel used. 2. Design limitations of the engine. 3. Degree of supercharging. 4. Spark plug reach. A— Four. B— Two. C— Three.

A full-floating piston pin is free to rotate in both the piston and the small end of the connecting rod. Full-floating piston pins are usually a push fit in the piston. They are kept from damaging the cylinder walls as they move up and down by soft aluminum or brass plugs in the ends of the pin.

8036. Full-floating piston pins are those which allow motion between the pin and A— the piston. B— both the piston and the large end of the connecting rod. C— both the piston and the small end of the connecting rod.

Valve overlap is the angular travel of the crankshaft during the time both the intake and exhaust valves are off their seats, and is used to increase the volumetric efficiency of the engine. The exhaust valve remains open until after the piston has started down on the intake stroke to allow the maximum amount of burned exhaust gases to leave the cylinder. The intake valve opens shortly before the piston reaches the top of its travel on the exhaust stroke. The inertia of the exhaust gases leaving the cylinder when the intake valve opens, helps start the fresh fuel-air charge flowing into the cylinder. By timing the valves and ignition to occur at the proper time, the mixture will not be burning as the piston is moving downward, and the cylinder walls will not become overheated.

8037. The primary purpose in setting proper valve timing and overlap is to A— permit the best possible charge of fuel/air mixture into the cylinders. B— gain more thorough exhaust gas scavenging. C— obtain the best volumetric efficiency and lower cylinder operating temperatures.

The cylinder head of an air-cooled engine expands much more than the pushrod. Because of this, air-cooled engines equipped with solid valve lifters (this applies primarily to radial engines) have a much larger valve clearance when the engine is hot than when it is cold. if the valves are adjusted to the hot (running) clearance when the cylinder is cold, the clearance in the valve train will be too great when the engine is at its normal operating temperature. The valves will open late and close early. The cam will have to turn farther to open the valve and the valve will close before the cam has turned to the normal valveclosing position.

8038. If the hot clearance is used to set the valves when the engine is cold, what will occur during operation of the engine? A— The valves will open early and close early. B— The valves will open late and close early. C— The valves will open early and close late.

Every mechanical device has a resonant frequency. If the valve is operating at the resonant frequency of the valve spring, the spring will lose its effectiveness and will surge, allowing the valve to float. By using two or more valve springs wound with a different pitch and a different size wire, the resonant frequency of the springs will be different and there will be no engine RPM at which the valves will float.

8039. The purpose of two or more valve springs in aircraft engines is to A— equalize side pressure on the valve stems. B— eliminate valve spring surge. C— equalize valve face loading.

Extreme care must be used if any water-mixed degreasing solutions containing caustic compounds of soap are used for cleaning engine parts. Such compounds, in addition to being potentially corrosive to aluminum and magnesium, may become impregnated in the pores of the metal and cause oil foaming when the engine is returned to service.

8040. During overhaul, the disassembled parts of an engine are usually degreased with some form of mineral spirits solvent rather than water-mixed degreasers primarily because A— solvent degreasers are much more effective. B— water-mixed degreaser residues may cause engine oil contamination in the overhauled engine. C— water-mixed degreasers cause corrosion.

One of the main factors that affect the smoothness of operation of a reciprocating engine is the closeness with which the power impulses are spaced. The greater the number of cylinders, the closer the power impulses are together and the smoother the engine will operate.

8041. Why does the smoothness of operation of an engine increase with a greater number of cylinders? A— The power impulses are spaced closer together. B— The power impulses are spaced farther apart. C— The engine has larger counterbalance weights.

The compression ratio of a reciprocating engine is the ratio of the volume of the cylinder with the piston at the bottom of its stroke to the volume of the cylinder with the piston at the top of its stroke.

8042. Compression ratio is the ratio between the A— piston travel on the compression stroke and on the intake stroke. B— combustion chamber pressure on the combustion stroke and on the exhaust stroke. C— cylinder volume with piston at bottom dead center and at top dead center.

Crankshaft run-out is measured by clamping a dial indicator to a solid part of the engine and placing the arm of the indicator against the part of the crankshaft where the run-out reading is to be measured. Place the indicator at Zero with the arm against the crankshaft. Rotate the crankshaft for a complete revolution. The total run-out is the difference between the negative and the positive readings. If the positive reading is +0.002 and the negative reading is -0.003, the total run-out is five thousandths of an inch (0.005 inch).

8043. If the crankshaft runout readings on the dial indicator are plus .002 inch and minus .003 inch, the runout is A— .005 inch. B— plus .001 inch. C— minus .001 inch.

Statement (1) is true. Only cast iron piston rings can be used in nitrided or chrome-plated cylinders. Statement (2) is also true. Chrome plated rings can be used in plain steel cylinders.

8044. (1) Cast iron piston rings may be used in chromeplated cylinders. (2) Chrome-plated rings may be used in plain steel cylinders. Regarding the above statements, A— only No. 1 is true. B— neither No. 1 nor No. 2 is true. C— both No. 1 and No. 2 are true.

The end gap in piston rings is measured by placing the piston ring inside the cylinder and pushing it up with the top of the piston so that it is square in the cylinder bore and in line with the cylinder flange. With the ring in this position, measure the distance between the two ends of the ring with a feeler gauge .

8045. How is proper end-gap clearance on new piston rings assured during the overhaul of an engine? A— By accurately measuring and matching the outside diameter of the rings with the inside diameter of the cylinders. B— By using rings specified by the engine manufacturer. C— By placing the rings in the cylinder and measuring the end-gap with a feeler gauge.

The compression ratio of a reciprocating engine is the ratio of the volume of a cylinder with the piston at the bottom of its stroke to the volume of the cylinder with the piston at the top of its stroke. If the cylinder has a volume of 70 cubic inches with the piston at the bottom of its stroke and 10 cubic inches with the piston at the top of its stroke, the compression ratio is 7:1.

8046. The volume of a cylinder equals 70 cubic inches when the piston is at bottom center. When the piston is at the top of the cylinder, the volume equals 10 cubic inches. What is the compression ratio? A— 1:7. B— 7:10. C— 7:1.

When cleaning aluminum and magnesium parts during engine overhaul, solutions containing soap should not be used, as it is very difficult to remove all traces of the soap. When the engine is assembled and operating, heat will bring out any soap remaining on the surface or in the pores of the metal. This soap will contaminate the engine oil and cause severe foaming.

8047. When cleaning aluminum and magnesium engine parts, it is inadvisable to soak them in solutions containing soap because A— some of the soap will become impregnated in the surface of the material and subsequently cause engine oil contamination and foaming. B— the soap can chemically alter the metals causing them to become more susceptible to corrosion. C— the parts can be destroyed by dissimilar metal electrolytic action if they are placed together in the solution for more than a few minutes.

A power check of a reciprocating engine is a check to determine that the engine is developing the correct static RPM and manifold pressure. The purpose of this check is to determine that the engine is performing satisfactorily.

8048. What is the purpose of a power check on a reciprocating engine? A— To check magneto drop. B— To determine satisfactory performance. C— To determine if the fuel/air mixture is adequate.

The joints of the piston rings must be staggered around the circumference of the piston in which they are installed to reduce blowby. If the gaps are not staggered, a differential compression check will give the indication of worn or defective rings

8049. What will be the likely result if the piston ring gaps happen to be aligned when performing a differential-pressure compression check on a cylinder? A— Little or no effect. B— The rings will not be seated. C— A worn or defective ring(s) indication.

if both the intake and exhaust valves in a cylinder have excessive clearance, the valve overlap period will be reduced. Valve overlap is the time between the end of the exhaust stroke and the beginning of the intake stroke when both valves are off of their seats. If the intake valve clearance is too great, the intake valve will open late. If the exhaust valve clearance is too great, the exhaust valve will close early. Late opening of the intake valve and early closing of the exhaust valve shorten the period of valve overlap.

8050. Which of the following will be caused by excessive valve clearance of a cylinder on a reciprocating aircraft engine? A— Reduced valve overlap period. B— Intake and exhaust valves will open early and close late. C— A power increase by shortening the exhaust event.

The floating-control thermostat controls the oil cooler airexit door. It maintains the oil temperature within the desired limits by controlling the air flow through the oil cooler.

8051. The floating control thermostat, used on some reciprocating engine installations, helps regulate oil temperature by A— controlling oil flow through the oil cooler. B— recirculating hot oil back through the sump. C— controlling air flow through the oil cooler.

The condition of an engine is shown by a full power check made with a fixed-pitch propeller or test club which furnishes a constant and a known load on the engine. If the engine is not producing its full power, it will not produce the correct static RPM at full throttle. The static RPM will be too low, and low static RPM with a fixed propeller load indicates a "weak" engine.

8052. Which of the following would indicate a general weak-engine condition when operated with a fixed-pitch propeller or test club? A— Lower than normal static RPM, full throttle operation. B— Manifold pressure lower at idle RPM than at static RPM. C— Lower than normal manifold pressure for any given RPM.

The only alternative listed here that must be included in a 100-hour inspection as specified in 14 CFR Part 43, Appendix D, is the cylinder compression check. A compression check, and specifically a differential compression check, tells much about the internal condition of the cylinders. It gives an indication of the seal provided by the valves and the condition of the piston rings.

8053. What is required by 14 CFR Part 43 Appendix D when performing an annual/100-hour inspection on a reciprocating engine aircraft? A— Magneto timing check. B— Cylinder compression check. C— Valve clearance check.

When spark plugs have been cleaned, gapped and tested, they should be installed in the cylinder next in firing order to the one from which they were removed, and they should be swapped from bottom to top.

8054. After spark plugs from an opposed engine have been serviced, in what position should they be reinstalled? A— Next in firing order to the one from which they were removed. B— Swapped bottom to top. C— Next in firing order to the one from which they were removed and swapped bottom to top.

When performing a differential compression check on a reciprocating engine, the piston of the cylinder being tested is placed on top center of the compression stroke and air is put into the cylinder. If the air causes the propeller to turn in the direction of normal rotation, the piston is not on top dead center, but is slightly past top center.

8055. As the pressure is applied during a reciprocating engine compression check using a differential pressure tester, what would a movement of the propeller in the direction of engine rotation indicate? A— The piston was on compression stroke. B— The piston was on exhaust stroke. C— The piston was positioned past top dead center.

Excessive clearance in the valve train will cause the valves to open late (the cam will have to turn farther before the valve is opened) and close early (the valve will close before the cam rotates to the normal closing position).

8056. Excessive valve clearance results in the valves opening A— late and closing early. B— early and closing late. C— late and closing late.

When you find any metal deposits in the lubricating-oil f ilters of an aircraft engine, you should investigate to find the source of the metal. If the metal particles are not attracted by the mag netic drain plug, they are from either the plain bearings or the pistons.

8057. During routine inspection of a reciprocating engine, a deposit of small, bright, metallic particles which do not cling to the magnetic drain plug is discovered in the oil sump and on the surface of the oil filter. This condition A— may be a result of abnormal plain type bearing wear and is cause for further investigation. B— is probably a result of ring and cylinder wall wear and is cause for engine removal and/or overhaul. C— is normal in engines utilizing plain type bearings and aluminum pistons and is not cause for alarm.

Aircraft reciprocating engines are often mounted in a type of suspension called dynamic suspension, or dyna-focal engine mounts. Dyna-focal mounts absorb the vibrations of the engine about the center of gravity of the engine-propeller combination and isolates these vibrations from the aircraft structure. The shock mounts all point toward the engine-propeller center of gravity.

8058. A characteristic of dyna-focal engine mounts as applied to aircraft reciprocating engines is that the A— shock mounts eliminate the torsional flexing of the powerplant. B— engine attaches to the shock mounts at the engine's center of gravity. C— shock mounts point toward the engine's center of gravity.

Anytime metallic particles are found on the oil screen of an aircraft engine, their source and the cause for their being in the oil system must be determined and corrected before the aircraft is released for flight.

8059. If metallic particles are found in the oil filter during an inspection, A— it is an indication of normal engine wear unless the particles are nonferrous. B— the cause should be identified and corrected before the aircraft is released for flight. C— it is an indication of normal engine wear unless the deposit exceeds a specified amount.

Oil pressure fluctuation ranging from zero to the normal operating pressure is most likely caused by a low oil supply. When the pump picks up oil, the pressure is normal, but when it draws air, the pressure drops to zero.

8060. If the oil pressure gauge fluctuates over a wide range from zero to normal operating pressure, the most likely cause is A— low oil supply. B— broken or weak pressure relief valve spring. C— air lock in the scavenge pump intake.

Some large radial engines have floating cam rings. A floating cam ring is held centered over its bearing by the forces exerted by the valve springs. When checking the valve clearance on an engine equipped with a floating cam, the bearing clearance must be eliminated by depressing two valves on the opposite side of the engine from the valves being checked. Depressing the valves removes the pressure of their valve spring from the cam allowing the cam ring to move tight against its bearing on the side where the valves are being checked.

8061. What special procedure must be followed when adjusting the valves of an engine equipped with a floating cam ring? A— Adjust valves when the engine is hot. B— Adjust all exhaust valves before intake valves . C— Eliminate cam bearing clearance when making valve adjustment.

Overhead valves in an air-cooled engine have their smallest clearance when the engine is cold. This clearance opens up to several times the cold clearance when the engine is at its operating temperature. If the valve clearance is too small, the valves will likely not seat positively when the engine is cold during start and engine warm-up.

8062. Which of the following is most likely to occur if an overhead valve engine is operated with inadequate valve clearances? A— The valves will not seat positively during start and engine warmup. B— The further decrease in valve clearance that occurs as engine temperatures increase will cause damage to the valve-operating mechanism. C— The valves will remain closed for longer periods than specified by the engine manufacturer.

Excessive valve clearance will cause the valves to remain open for a shorter period of time than they would have with a normal clearance. The cam must turn farther to open the valve and the valve will close before the cam has turned to the correct valve-closing position.

8063. Excessive valve clearances will cause the duration of valve opening to A— increase for both intake and exhaust valves. B— decrease for both intake and exhaust valves. C— decrease for intake valves and increase for exhaust valves.

Valve overlap is the portion of crankshaft rotation during which both the intake and the exhaust valves are off of their seats at the same time. Adequate valve overlap increases the volumetric efficiency of the engine. It aids in the scavenging of the burned exhaust gases, and it gives the engine better cooling characteristics. This is done by ensuring that the fuel-air charge in the cylinder is rich enough for proper operation and not diluted with exhaust gases.

8064. What does valve overlap promote? A— Lower intake manifold pressure and temperatures. B— A backflow of gases across the cylinder. C— Better scavenging and cooling characteristics.

Each cylinder in a four-stroke-cycle engine fires every other revolution of the crankshaft. If a cylinder is to fire 200 times in one minute, the engine will have to be turning at 400 RPM.

8065. At what speed must a crankshaft turn if each cylinder of a four-stroke cycle engine is to be fired 200 times a minute? A— 800 RPM. B— 1,600 RPM. C— 400 RPM.

Crankshaft run-out is checked to determine whether the crankshaft of a reciprocating engine is bent. Crankshaft run-out is checked during each engine overhaul and after each sudden stoppage of the engine.

8066. Engine crankshaft runout is usually checked 1. during engine overhaul. 2. during annual inspection. 3. after a "prop strike" or sudden engine stoppage. 4. during 100-hour inspection. A— 1, 3, and 4. B— 1 and 3. C— 1, 2 and 3.

There are some cylinders below the center line of a radial engine, and it is possible for oil to drain down, past the piston rings, into these lower cylinders while the engine is not operating. When a radial engine has been shut down for a half hour or so, it should be checked for a liquid lock (oil in the lower cylinders) by pulling the propeller through in the direction of normal rotation by hand for at least two complete revolutions of the crankshaft. If oil has collected in any of the lower cylinders, the spark plugs must be removed from these cylinders and all of the oil drained out.

8067. Before attempting to start a radial engine that has been shut down for more than 30 minutes, A— turn the propeller by hand three or four revolutions in the opposite direction of normal rotation to check for liquid lock. B— turn the ignition switch on before energizing the starter. C— turn the propeller by hand three to four revolutions in the normal direction of rotation to check for liquid lock.

If an engine misses on both magnetos, the quickest way to f ind the cylinder that is not firing is by running the engine at the RPM at which it misses the most consistently and by feeling the exhaust stack at the cylinder head. The exhaust stack of the cylinder that is not firing will be much cooler than those of the cylinders that are firing normally.

8068. An engine misses in both the right and left positions of the magneto switch. The quickest method for locating the trouble is to A— check for one or more cold cylinders. B— perform a compression check. C— check each spark plug.

A hissing sound heard at the exhaust stacks when an aircraft engine is pulled through by hand is an indication that an exhaust valve is leaking. There is exhaust valve blow-by.

8069. A hissing sound from the exhaust stacks when the propeller is being pulled through manually indicates A— a cracked exhaust stack. B— exhaust valve blow-by. C— worn piston rings.

Many large aircraft reciprocating engines have a compensating oil pressure relief valve that allows the oil pressure for cold oil to be considerably higher than it allows for warm oil. This higher pressure allows the thicker, higher viscosity oil to be forced through the engine bearings. The plunger of the oil-pressure relief valve is held down by two springs when the oil is cold. However, when the oil warms up, a thermostatic valve opens and allows oil pressure to remove the force of one of the springs. For normal operation, only one spring holds the pressure relief valve on its seat.

8070. If the oil pressure of a cold engine is higher than at normal operating temperatures, the A— oil system relief valve should be readjusted. B— engine's lubrication system is probably operating normally. C— oil dilution system should be turned on immediately.

Some aircraft engines are equipped with an oil dilution system in which gasoline is put into the lubricating oil before the engine is shut down. Oil dilution is used in cold weather to make a cold engine easier to start. If an oil dilution valve should leak and allow gasoline to flow into the oil supply during normal operation, it will cause the oil to be too thin (to have too low a viscosity) for normal operation. The oil pressure will drop and the oil temperature will go up.

8071. If an engine operates with a low oil pressure and a high oil temperature, the problem may be caused by a A— leaking oil dilution valve. B— sheared oil pump shaft. C— clogged oil cooler annular jacket.

Lean mixtures burn more slowly than rich mixtures and a mixture leaner than the manual-lean mixture of 0.060, or approximately 17:1, will possibly be burning as the gases are forced out past the exhaust valve. This will cause serious overheating of the exhaust valve.

8072. Which fuel/air mixture will result in the highest engine temperature (all other factors remaining constant)? A— A mixture leaner than a rich best-power mixture of .085. B— A mixture richer than a full-rich mixture of .087. C— A mixture leaner than a manual lean mixture of .060.

When removing a cylinder from an aircraft engine, rotate the crankshaft until the piston is at top center on the compression stroke. In this position, the pushrods can be most easily removed. The piston will be all the way out of the crankcase so the wrist pin can be slipped out to remove the piston with the cylinder.

8073. If an engine cylinder is to be removed, at what position in the cylinder should the piston be? A— Bottom dead center. B— Top dead center. C— Halfway between top and bottom dead center.

Indicated horsepower (IHP) is the horsepower developed in the cylinders of a reciprocating engine without reference to friction losses. Shaft horsepower and brake horsepower are the actual usable powers that do include friction losses.

8074. The horsepower developed in the cylinders of a reciprocating engine is known as the A— shaft horsepower. B— indicated horsepower. C— brake horsepower.

One of the required characteristics of an aircraft engine is operating flexibility. Operating flexibility is defined by the FAA as the ability of an engine to run smoothly and to give the desired performance at all speeds.

8075. Engine operating flexibility is the ability of the engine to A— deliver maximum horsepower at a specific altitude. B— meet exacting requirements of efficiency and low weight per horsepower ratio. C— run smoothly and give the desired performance at all speeds.

thin-walled aircraft-engine cylinders may be ground oversize, but the amount they may be ground is much less than is allowed for the much thicker-walled cylinders normally used in automobile engines. Some aircraft-engine cylinders may not be re-bored at all. The engine manufacturer's recommendations must be followed in detail regarding any re-boring operation.

8076. Standard aircraft cylinder oversizes usually range from 0.010 inch to 0.030 inch. Oversize on automobile engine cylinders may range up to 0.100 inch. This is because aircraft engine cylinders A— have more limited cooling capacity. B— have relatively thin walls and may be nitrided. C— operate at high temperatures.

All certificated aircraft reciprocating engines have dual ignition. During normal operation, both ignition systems are operating. During a magneto check, the engine is operated at the speed specified by the engine manufacturer and the ignition system is switched from BOTH magnetos to each magneto separately. When the engine operates on a single magneto, the fuel-air mixture in the cylinder is ignited at one point only causing a slight drop in engine power. The RPM will drop slightly.

8077. If the ignition switch is moved from BOTH to either LEFT or RIGHT during a magneto check, a normal operation is usually indicated by A— no change in RPM. B— a momentary interruption of both ignition systems. C— a slight drop in RPM.

A dead cylinder will cause an engine to run rough. Because the throttle will have to be opened farther to get the same RPM, the manifold pressure will be higher than it would on an engine with all the cylinders firing. A dead cylinder will not show up on a magneto check.

8078. During ground check an engine is found to be rough-running, the magneto drop is normal, and the manifold pressure is higher than normal for any given RPM. The trouble may be caused by A— several spark plugs fouled on different cylinders . B— a leak in the intake manifold. C— a dead cylinder.

High oil consumption is the only alternative that would indicate worn valve guides. When the valve guide wears, oil from the rocker box f lows down the valve stem and is burned.

8079. What is the best indication of worn valve guides? A— High oil consumption. B— Low compression. C— Low oil pressure.

In a nine-cylinder radial engine, each cylinder fires 80° of crankshaft rotation after the cylinder before it, in firing order. When the crankshaft is rotated 260° after the piston in cylinder number one is at top dead center on its compression stroke, the piston in cylinders 7 and 8 are near the top of their strokes. The piston in cylinder 3 is near the bottom of its power stroke and its exhaust valve is open. It is normal for a cylinder not to hold air pressure when its piston is near the bottom of its power stroke and its exhaust valve is open.

8080. By use of a differential pressure compression tester, it is determined that the No. 3 cylinder of a nine-cylinder radial engine will not hold pressure after the crankshaft has been rotated 260° from top dead center compression stroke No. 1 cylinder. How can this indication usually be interpreted? A— A normal indication. B— Exhaust valve blow-by. C— A damaged exhaust valve or insufficient exhaust valve clearance.

both the intake and exhaust valve are open at the same time, only during the period of valve overlap. Valve overlap occurs at the end of the exhaust stroke and the beginning of the intake stroke. The intake valve opens a few degrees of crankshaft rotation before the piston reaches the top of the exhaust stroke. The exhaust valve remains open until the piston has moved down a few degrees of crankshaft rotation on the intake stroke.

8081. When does valve overlap occur in the operation of an aircraft reciprocating engine? — At the end of the exhaust stroke and the beginning of the intake stroke. B— At the end of the power stroke and the beginning of the exhaust stroke. C— At the end of the compression stroke and the beginning of the power stroke.

Some aircraft engine exhaust valves are hollow and are partially filled with metallic sodium. When the engine is operating, the sodium melts and as the valve opens and closes, the molten sodium sloshes back and forth in thevalve. When it is in the head, it absorbs heat. When it is in the stem, it transfers this heat to the valve guides. Sodium-filled valves reduce the valve operating temperature.

8082. What is an advantage of using metallic-sodium f illed exhaust valves in aircraft reciprocating engines? A— Increased strength and resistance to cracking. B— Reduced valve operating temperatures. C— Greater resistance to deterioration at high valve temperatures.

When assembling an opposed engine equipped with hydraulic valve lifters, if the valve clearance is not within the allowable limits, install a pushrod of a slightly different length.

8083. Valve clearance changes on opposed-type engines using hydraulic lifters are accomplished by A— rocker arm adjustment. B— rocker arm replacement. C— push rod replacement.

No aircraft engine should be operated at high power settings before it is properly warmed up and the oil is warm enough to flow freely through all the passages. High power operation with cold oil can cause oil starvation to the bearings.

8084. What is likely to occur if a reciprocating engine is operated at high power settings before it is properly warmed up? A— Oil starvation of bearings and other parts. B— Excessive thinning of the engine oil. C— Accelerated oil breakdown and oxidation.

the cylinder pressure applied to the crankshaft through the connecting rod bearings is determined by the compression ratio of the engine and the manifold pressure. If the manifold pressure for a given RPM is increased, the bearing load imposed on the crankshaft will increase.

8085. An increase in manifold pressure with a constant RPM will cause the bearing load in an engine to A— decrease. B— remain relatively constant. C— increase.

When rigging any engine control in an aircraft, the stop on the component being actuated must be contacted before the stop in the cockpit. The control linkage has enough spring-back in both directions that after the stop on the diverter valve is contacted, the control can be moved in both directions until it contacts the stop in the cockpit. When the control is released, it will spring back a few degrees.

8086. Direct mechanical push-pull carburetor heat control linkages should normally be adjusted so that the stop located on the diverter valve will be contacted A— before the stop at the control lever is reached in both HOT and COLD positions. B— before the stop at the control lever is reached in the HOT position and after the stop at the control lever is reached in the COLD position. C— after the stop at the control lever is reached in both HOT and COLD positions.

An aircraft engine produces power by converting the chemical energy in the fuel into heat energy as the fuel-air mixture is burned inside the engine cylinders. The efficiency of this energy interchange is determined by the ratio between weight of the air and the weight of the fuel in the mixture. The air at high altitude is less dense (weighs less) than the air at sea level, and the fuel metered into the same volume of air will cause the fuel-air mixture at high altitude to become excessively rich. There will be too many pounds of fuel per pound of air for the most efficient production of power.

8087. Reduced air density at high altitude has a decided effect on carburetion, resulting in a reduction of engine power by A— excessively enriching the fuel/air mixture. B— excessively leaning the fuel/air mixture. C— reducing fuel vaporization.

The amount of energy released by a burning fuel-air mixture is determined by the weight of both the fuel and the air in the mixture. Water vapor weighs only about 5/8 as much as dry air, and when an engine takes in air with a high relative humidity, it produces less power at the same RPM and manifold pressure than it would produce if it were taking in dry air.

8088. Increased water vapor (higher relative humidity) in the incoming air to a reciprocating engine will normally result in which of the following? A— Decreased engine power at a constant RPM and manifold pressure. B— Increased power output due to increased volumetric efficiency. C— A leaning effect on engines which use nonautomatic carburetors.

Statement (1) is not true. Preignition is the ignition of the fuel-air mixture before normal ignition is timed to occur. It is caused by incandescent objects in the cylinder. Detonation produces enough heat in a cylinder that carbon particles can become incandescent and ignite the mixture early. Statement (2) is not true. Detonation is the spontaneous combustion of the unburned charge ahead of the flame front after ignition has occurred. Preignition can cause the fuel-air mixture to burn in the cylinder long enough to heat the unburned mixture to its critical temperature. At this point, it explodes rather than burns. This instantaneous release of energy can overheat the cylinder producing enough pressure to damage the piston and connecting rod.

8089. (1) Preignition is caused by improper ignition timing. (2) Detonation occurs when an area of the combustion chamber becomes incandescent and ignites the fuel/air mixture in advance of normal timed ignition. Regarding the above statements, A— only No. 1 is true. B— both No. 1 and No. 2 are true. C— neither No. 1 nor No. 2 is true.

When a new or freshly overhauled engine is installed in an aircraft, it must be pre-oiled. The oil tank is filled, and oil is pumped through all the passages until pressure registers on the oil pressure gauge in the cockpit. Pre-oiling ensures that all the bearings will be adequately lubricated before the oil pump begins to pump oil through the system normally.

8090. Which of the following engine servicing operations generally requires engine pre-oiling prior to starting the engine? A— Engine oil and filter change. B— Engine installation. C— Replacement of oil lines.

When installing push-pull control rods in an aircraft, you can determine that the rod end is properly screwed onto the rod by trying to pass a piece of safety wire through the inspection hole in the rod. If the rod end is screwed into the rod far enough to cover the hole, there are enough threads engaged to give the connection the full strength required.

8091. During the inspection of an engine control system in which push-pull control rods are used, the threaded rod ends should A— insure that the safety wire passes through the hole in shank of the rod-end. B— be checked for thread engagement of at least two threads but not more than four threads. C— be checked for the amount of thread engagement by means of the inspection holes.

Detonation is an uncontrolled burning of the fuel inside the engine cylinders. The fuel-air mixture actually explodes, rather than burning evenly as it should. The octane rating of a fuel is a measure of its detonation resistance. If a fuel with too low an octane rating is used, the fuel-air mixture is likely to detonate when the engine is developing full power.

8092. Which of the following conditions would most likely lead to detonation? A— Late ignition timing. B— Use of fuel with too high an octane rating. C— Use of fuel with too low an octane rating.

The power produced by an aircraft reciprocating engine is determined by the weight of the air that is mixed with the fuel and burned. At altitude, the density of the air (its weight per unit volume) is less than it is at sea level. Therefore, for the same RPM, a unsupercharged engine will take in less weight of air to combine with the fuel and the engine will lose power.

8093. An unsupercharged aircraft reciprocating engine, operated at full throttle from sea level, to 10,000 feet, provided the RPM is unchanged, will A— lose power due to the reduced volume of air drawn into the cylinders. B— produce constant power due to the same volume of air drawn into the cylinders. C— lose power due to the reduced density of the air drawn into the cylinders.

A lean fuel-air mixture burns slower than either a rich or a chemically-correct mixture. There is a possibility that a lean mixture will still be burning as it is pushed out through the exhaust valve. During the time of valve overlap, when both the intake and the exhaust valves are open, the burning exhaust gases can ignite the fresh fuel-air charge being taken into the cylinder through the intake valve. This can cause a backfire through the induction system.

8094. Which of the following would most likely cause a reciprocating engine to backfire through the induction system at low RPM operation? A— Idle mixture too rich. B— Clogged derichment valve. C— Lean mixture.

When pre-oiling a dry-sump reciprocating engine, you know there is oil in all the passages when oil flows from the engine return line or from the port to which the oil pressure gauge is connected.

8095. How may it be determined that a reciprocating engine with a dry sump is pre-oiled sufficiently? A— The engine oil pressure gauge will indicate normal oil pressure. B— Oil will flow from the engine return line or indicator port. C— When the quantity of oil specified by the manufacturer has been pumped into the engine.

When reducing the power of an engine equipped with a constant-speed propeller, it is important that the manifold pressure be reduced by retarding the throttle before the RPM is reduced with the propeller pitch control. If the wrong sequence is used, the high manifold pressure and the low RPM can produce cylinder pressures high enough to seriously damage the engine.

8096. What is the basic operational sequence for reducing the power output of an engine equipped with a constantspeed propeller? A— Reduce the RPM, then the manifold pressure. B— Reduce the manifold pressure, then retard the throttle to obtain the correct RPM. C— Reduce the manifold pressure, then the RPM.

The fuel-air mixture used for the engine to produce its best power is richer (there is more fuel for the air) than a mixture that gives the maximum economy. The best power mixture is about a 12:1 mixture (12 parts of air to one part of fuel), and the maximum economy mixture is about 16:1.

8097. Which statement pertaining to fuel/air ratios is true? A— The mixture ratio which gives the best power is richer than the mixture ratio which gives maximum economy. B— A rich mixture is faster burning than a normal mixture. C— The mixture ratio which gives maximum economy may also be designated as best power mixture.

Backfiring through the carburetor is often caused by the use of an extremely lean mixture. A lean mixture burns slowly. If it is still burning when the intake valve opens, the burning mixture will ignite the fresh fuel-air charge and cause a backfire in the induction system.

8098. Backfiring through the carburetor generally results from the use of A— an excessively lean mixture. B— excessively atomized fuel. C— an excessively rich mixture.

Detonation occurs when the fuel-air mixture burning in a cylinder reaches its critical pressure and temperature. Detonation may be caused by the high pressure and temperature resulting from high manifold pressure, high intake air temperature, or an overheated engine. Late ignition timing reduces engine power but it does not cause detonation.

8099. Which of these conditions will cause an engine to have an increased tendency to detonate? 1. High manifold pressure. 2. High intake air temperature. 3. Engine overheated. 4. Late ignition timing. A— 1, 4. B— 1, 2, 3. C— 1, 2, 3, 4.

small induction-system air leak will have the most noticeable effect on engine operation when the engine is operating at low RPM. At the low engine speed, the volume of air entering the cylinders is small. Because of this, the additional air coming in through the leak makes an appreciable change in the fuel-air mixture ratio. At higher RPMs, so much air is being taken into the cylinders that the amount that leaks into the system does not change the ratio enough to make a big difference.

8100. When will small induction system air leaks have the most noticeable effect on engine operation? A— At high RPM. B— At maximum continuous and takeoff power settings. C— At low RPM.

Radial and inverted engines have some cylinders below the crankcase, and when the engine is idle, oil will leak from the crankcase, past the piston rings, and fill the combustion chamber. This condition is called a hydraulic lock. If this oil is not removed before the engine is started, the piston will move against the noncompressible oil and cause serious damage.

A condition that can occur in radial engines but is unlikely to occur in horizontally opposed engines is A— oil-fouled spark plug. B— valve overlap. C— hydraulic lock.

The smaller contact area of a ball bearing causes it to produce less rolling friction than a roller bearing. Ball bearings are used in high-powered reciprocating engines, where keeping friction to a minimum is important. Ball bearings can be designed and installed in such a way that they reduce friction in axial loads as well as in radial loads.

Which statement is true regarding bearings used in high-powered reciprocating aircraft engines? A— The outer race of a single-row, self-aligning ball bearing will always have a radius equal to the radius of the balls. B— There is less rolling friction when ball bearings are used than when roller bearings are employed. C— Crankshaft bearings are generally of the ball-type due to their ability to withstand extreme loads without overheating.