Chapter 7

Front 1

The engine powertrain comprises what?

Back 1

For purposes of study, the engine powertrain comprises those engine components responsible for delivering the power developed in the engine cylinders to the power takeoff mechanism, usually a flywheel.

Front 2

Where were and are aluminum trunk-type pistons used and why?

Back 2

Aluminum trunk-type pistons were widely used in medium-and large-bore diesel engines until the late 1980s because of their light weight and ability to rapidly transfer heat. They are still used today but mostly in light duty diesel engines.

Front 3

How is the top compression ring supported in aluminum alloy trunk-type pistons used in diesel engines? What is their shape and why?

Back 3

Aluminum alloy trunk-type pistons used in diesel engines support the top compression ring with an Ni-Resist insert. They are also cam ground and tapered due to the way they expand in operation.

Front 4

What type of piston assembly replaced what type of piston assembly?

Back 4

Two-piece, articulating piston assemblies replaced aluminum trunk pistons and until recently were the favored piston design by engine OEMs.

Front 5

What do articulating pistons usually consist of?

Back 5

Articulating pistons usually consist of a forged steel crown and aluminum alloy skirt. The two pieces are coupled to the wrist pin, which affords each some independent movement.

Front 6

Today, what material do diesel engine OEMs favor for their pistons in their high-output engines? What are the Magle versions of these known as? The Federal Mogul version?

Back 6

Today, diesel engine OEMs favor forged or composite steel trunk pistons in their high-output engines. The Mahle versions of these are known as Monotherm and Monocomp pistons, while the Federal Mogul version is known as a Monosteel piston.

Front 7

What do steel trunk pistons use to reduce mass and piston drag?

Back 7

Steel trunk pistons use high-strength alloy steels and reduced skirt contact area to reduce mass and piston drag.

Front 8

What is the most common piston in today’s low emissions, direct-injected diesel engines?

Back 8

The Mexican hat piston crown, open combustion chamber is the most common in today’s low emissions, direct-injected diesel engines.

Front 9

In what ways is engine oil used to help cool pistons?

Back 9

Engine oil is used to help cool pistons in three ways: shaker, circulation, and spray jet methods.

Front 10

When do piston rings seal, what happens then, and what does it mean?

Back 10

Piston rings seal when cylinder pressure acts on the exposed sectional area of the ring, which first forces it down into the land, and then gets behind it to load the ring face into the cylinder wall. This means that the efficiency with which piston rings seal a cylinder increases proportionally with cylinder pressure.

Front 11

What are blowby gases?

Back 11

Gases that manage to pass by the piston rings, enter the crankcase, and are known as blowby gases.

Front 12

What design is commonly used for the top compression ring in today’s highway diesel engines?

Back 12

The keystone ring design is commonly used for the top compression ring in today’s highway diesel engines.

Front 13

Oil control rings are designed to do what? What do the piston rings do?

Back 13

Oil control rings are designed to apply a film of oil to the cylinder wall on the upstroke of the piston and “scrape” it on the downstroke. All the piston rings play a role in controlling the oil film on the cylinder.

Front 14

What do full-floating wrist pins have? What do crosshead have?

Back 14

Full-floating wrist pins have a bearing surface with both the piston boss and the connecting rod eye. Crosshead pistons articulate but have a semifloating wrist pin that bolts directly to the rod small end.

Front 15

How are full-floating wrist pins retained in the piston boss?

Back 15

Full-floating wrist pins are retained in the piston boss by snaprings.

Front 16

How do DDC two-stroke cycle engines seal the pin boss between the piston pin and the air box?

Back 16

DDC two-stroke cycle engines use press fit caps to seal the pin boss between the piston pin and the air box.

Front 17

What forces are connecting rods subjected to in normal service operation?

Back 17

Connecting rods are subjected to compressional and tensional loads in normal service operation.

Front 18

How many connecting rods survive the life of the engine and when should they be inspected?

Back 18

Most connecting rods will survive the life of the engine, but they should be dimensionally and crack inspected at each overhaul.

Front 19

Crankshafts must be designed to withstand what?

Back 19

Crankshafts must be designed to withstand considerable bending and torsional stress.

Front 20

What kind of crankshaft do most medium- and large-bore highway diesel engines use?

Back 20

Most medium- and large-bore highway diesel engines use induction-hardened crankshafts.

Front 21

How common is reconditioning failed crankshafts?

Back 21

Engine OEMs often do not approve of reconditioning failed crankshafts; however, the practice is widespread despite the risk of a subsequent failure.

Front 22

How are friction bearings in crankshaft throw and main journals retained?

Back 22

Friction bearings used in crankshaft throw and main journals are retained by crush.

Front 23

What do vibration dampers consist of?

Back 23

Vibration dampers consist of a drive member, drive medium, and inertia ring.

Front 24

What type of damper is most commonly used on today’s trucks and bus diesels? How does it work?

Back 24

The viscous-type damper is the most commonly used on today’s truck and bus diesels. The hollow drive ring is bolted directly to the crankshaft, and suspended in gelled silicone is the inertia ring. The shearing action of the silicone drive medium between the drive ring and the inertia ring affects the damping.

Front 25

What does the flywheel do?

Back 25

The flywheel stores kinetic energy in the form of inertia to help smooth out the power pulses delivered to the engine powertrain.

Front 26

How are flywheels categorized and by whom?

Back 26

Flywheels are categorized by size and shape by the SAE.

Front 27

What engine condition would be the likely cause of a tensile failure of a connecting rod?

Back 27

Engine overspeed

Front 28

Which of the following is a disadvantage of an articulating piston assembly when comparing it to an aluminum alloy trunk piston?

Back 28

Increased tensile loading on the connecting rods due to significantly increased weight

Front 29

Where would a Ni-Resist insert be located?

Back 29

Upper ring belt, aluminum trunk piston

Front 30

What is the drive medium of a viscous damper?

Back 30

A fluid, such as silicone gel.

Front 31

What does a piston assembly consist of?

Back 31

The piston assembly consists of the piston, piston rings, and a wrist pin.

Front 32

What are trunk-type pistons?

Back 32

Trunk-type pistons are single-piece pistons consisting of a crown and integral skirt.

Front 33

What are the two types of articulating piston assemblies used in commercial diesel engines?

Back 33

Two types of articulating piston assemblies are used in commercial diesel engines:Crosshead pistonsFull articulating pistons

Front 34

What are crosshead pistons?

Back 34

Differentiated by the use of a semifloating wrist pin bolted to the connecting rod.

Front 35

What are full articulating pistons?

Back 35

Use a full-floating wrist pin that permits pivot on the connecting rod eye, crown, and skirt assemblies.

Front 36

What are the categories of trunk-type pistons used in diesel engines today?

Back 36

There are three categories of trunk-type pistons used in diesel engines today:Aluminum trunk pistonsForged steel trunk pistonsComposite steel trunk pistons

Front 37

What is the disadvantage of a cam ground?

Back 37

The disadvantage of cam ground pistons is that they should be warmed to operating temperature before being subjected to high cylinder pressures. Failure to properly warm cam ground pistons before loading an engine can overstress the piston rings and piston lands.

Front 38

How do you help pin assembly?

Back 38

Heating the piston to 95°C (200°F) in boiling water facilitates pin assembly.

Front 39

What is piston slap?

Back 39

Piston slap is the tilting action of the piston when the piston is thrust loaded by cylinder combustion pressure.

Front 40

What are the advantages of aluminum trunk pistons?

Back 40

Lightweight

Cooler piston crown temperatures

Quieter

Front 41

What are the advantages of steel trunk pistons?

Back 41

Reduction of headland volume

Thermal expansion factors

Longevity

Lightweight

Front 42

What are the roles of piston rings?

Back 42

Sealing, lubrication and cooling

Front 43

Where do you inspect on crankshaft and bearings?

Back 43

Inspect seal areas, front and back.

Inspect dowels on flywheel side to make sure they’re not worn.

Inspect the journals and mains in line.

Inspect main and rod journals and dowels.

Cracks - scratches - hot spots.

Fillet areas.

Thrust areas.

Gear area.

Key area.

Front 44

What are the causes of bending break (90 degrees) crankshaft failures?

Back 44

Too sharp filet

misaligned main caps

loose cap - excess end thrust

misaligned block

misaligned accessories (PIO - Air Comp Fan Hubs)

Front 45

What are the causes of torsional break (45 degrees) crankshaft failures?

Back 45

Damaged vibration damper

Engine overspeed

Unbalanced load

Loose flywheel

Over tight belt driven acc

After market acc

Front 46

What are the causes of bearing seizure crankshaft failures?

Back 46

Spun bearing

Improper torque

Dirty or clogged oil passages

Excess oil temperatures

Wrong oil

Coolant in the oil

Front 47

Under which of the following conditions would a piston ring seal more effectively?

Back 47

High cylinder pressures

Front 48

A crankshaft has a fracture failure that appears to have initiated at a throw journal oil hole. What could be the cause?

Back 48

A failed vibration damper (most important one to remember), unbalanced engine-driven components, engine overspeed, unbalanced cylinder loading, defective engine mounts.

Front 49

What journal surface hardening method would provide the highest machinability margin?

Back 49

Induction hardening

Front 50

Rod and main journal bearing clearances are properly measured with what?

Back 50

Plastigage

Front 51

What type of piston is favored by diesel engine OEMs in post-2007 products?

Back 51

Forged or composite steel trunk pistons

Front 52

When observing a disassembled engine, the outer crown edges of all six pistons show signs of melting and erosion. This could be caused by:

Back 52

Fuel with high sulfur content

Front 53

Which of the following types of pistons use bushingless pin bosses?

Back 53

Monotherm

Front 54

What would be the consequence of a misdirected piston oil cooling jet?

Back 54

Torched piston

Front 55

What design of piston ring is most common in current diesel engines?

Back 55

Keystone ring

Front 56

Keystone connecting rods are shaped like what?

Back 56

Wedge-shaped big end.

Front 57

What should be used to install piston rings onto a piston?

Back 57

An OEM ring expander

Front 58

Which of the following operating modes would be more likely to result in a compressional failure of a connecting rod?

Back 58

Hydraulic lock caused by head gasket failure

Front 59

Which of the following would be the more likely outcome of running an engine with a failed vibration damper?

Back 59

Crankshaft failure

Front 60

In what area of a Mexican hat combustion chamber are the injected droplets of fuel directed?

Back 60

Center of the cone protrusion

Front 61

The upper face of a piston assembly is called the:

Back 61

Crown

Front 62

What is a major disadvantage of the articulating pistons over the aluminum trunk design?

Back 62

Significantly increased weight, which increases tensional loading on the powertrain.

Front 63

What are the advantages of articulating pistons?

Back 63

Greater longevity

Reduced piston slap

More durable crown assembly

Reduced headland volume

Front 64

Excessive clearance at the crankshaft main bearings could result in which of the following conditions?

Back 64

Low oil pressure