RECIPROCATING ENGINES

Question 1

How are conventional reciprocating engines classified?

Answer 1

They are classified according to cylinder arrangement with respect to the crankshaft (in-line, Vtype, radial, and opposed), or according to method of cooling (liquid cooled or air cooled).

Question 2

What are the different types of piston rings?

Answer 2

Compression rings, oil control rings, and scraper rings

Question 3

What is the purpose of the oil control rings?

Answer 3

They are used to control the thickness of the oil film on the cylinder walls.

Question 4

What may be the result of installing piston rings incorrectly?

Answer 4

Excessive oil consumption

Question 5

What types of piston rods are commonly found in radial engines?

Answer 5

A master and articulating rod assembly

Question 6

What types of bearings are in general use in reciprocating engines?

Answer 6

Plain bearings, which are generally used for crankshaft cam ring, camshaft, connecting rods,
and accessory drive shaft bearings. Roller bearings, which are used primarily as crankshaft
main bearings but have other applications, as well. Ball bearings, which are used for
supercharger impeller shaft bearings, rocker arm bearings in some engines, and as propeller
thrust bearings.

Question 7

What is the indication of valve blow-by?

Answer 7

Valve blow-by is indicated by a hissing or whistle when pulling the propeller through, prior to
starting the engine. A cylinder compression check should be made to identify the faulty
cylinder.

Question 8

What is the purpose of using more than one spring for valve closing?

Answer 8

A valve spring will resonate (or surge) at certain engine speeds. When the spring resonates, it
loses its ability to keep the valve closed and the valve begins to float. By using two springs
(different sizes, one inside the other) this problem is eliminated. The springs will resonate at
separate engine speeds so the valve is always held closed by at least one spring.

Question 9

What is the purpose of valve overlap?

Answer 9

Valve overlap permits better volumetric efficiency and lowers the cylinder operating
temperatures.

Question 10

Describe the inspection you would give the valve springs during engine overhaul

Answer 10

They should be cleaned thoroughly and then visually inspected for evidence of overheating,
cracks, broken ends, and for compression strength.

Question 11

What is the purpose of using valves with sodium-filled stems?

Answer 11

Some intake and exhaust valve stems are hollow and partially filled with metallic sodium.
Sodium is used because it is an excellent heat conductor. The sodium melts at about 208º F.
and the movement of the valves circulates the liquid sodium which enables it to carry the heat
from the valve head to the stem, where it is dissipated through the value guide to the cylinder
head and cooling fins.

Question 12

What causes engine sudden stoppage?

Answer 12

Striking an object or engine seizure due to internal damage

Question 13

What type inspection must be made after sudden stoppage of an engine due to striking an object?

Answer 13

The propeller drive shaft must be checked for misalignment and the propeller checked for track

Question 14

What is the purpose of crankshaft dynamic dampers used in aircraft engines?

Answer 14

Dampers are used to overcome forces that cause deflection of the crankshaft and torsional
vibration. These forces are generated by the power impulses of the pistons. Crankshaft
vibrations are reduced by placing floating dampers (weights) in the counterweight assembly,
particularly in a single throw-type crankshaft.

Question 15

How would you make a ―runout‖ check on a crankshaft that is still installed in the engine?

Answer 15

Remove the propeller from the shaft and attach a dial indicator gauge to the front of the
crankcase. Adjust the position of the gauge needle so that it is touching the shaft. Turn the
engine through with the starter and note any changes in the gauge reading.

Question 16

What is detonation?

Answer 16

Normal combustion is when the fuel-air mixture burns at a uniform rate across the combustion
chamber. The temperature and pressure within the cylinder rises at a normal rate as the mixture
burns. All fuels have critical limits of temperature and compression, and beyond this limit, they
will ignite spontaneously and burn with explosive violence. This instantaneous explosive
burning of the last portion of the charge is called the detonation.

Question 17

During valve clearance adjustment on an R-2800 engine, why must you depress certain valves other than
the ones being adjusted?

Answer 17

The valves must be depressed (unloaded) in order to remove the pressure from the side
positions on the cam and thus permit the cam to slide away from the valves to be adjusted. This
prevents the cam from introducing errors in the valve clearance settings.

Question 18

What can be learned about the condition of an engine by studying the results of a compression check?

Answer 18

From the cylinder compression check you can determine if the valves, piston rings, and pistons
are adequately sealing the combustion chamber.

Question 19

How can a cold cylinder be located on a double-row radial engine?

Answer 19

A cold cylinder check can be made with a cold cylinder indicator, sometimes called a “magic
wand,” to locate any cylinder that has a temperature lower than the normal operating
temperature of the other cylinders.

Question 20

What instrument can be used to check a cylinder bore for out-of-roundness?

Answer 20

A cylinder bore can be checked with a dial indicator, a telescopic gauge and outside
micrometer, or an inside micrometer.