Chapter 8 Engines

Front 1

What do the engine feedback components include?

Back 1

The engine feedback components include:

- the engine timing geartrain

- the camshaft

- valve and unit injector trains

- and, in some cases, the injection pumping apparatus.

Front 2

Why must camshaft drive gears be precisely timed with the crankshaft driven engine geartrain?

Back 2

Camshaft drive gears must be precisely timed with the crankshaft-driven, engine geartrain so that the events activated by the engine feedback assembly are synchronized with those in the engine.

Front 3

What is the most often interference fit to the camshift and what is it positioned by?

Back 3

The camshaft drive gear is most often interference fit to the camshaft and positioned by a keyway.

Front 4

When camshaft gears are fitted to camshafts, what is done to them? What does this entail? What is one thing to watch out for?

Back 4

Camshaft gears are heat treated when they are fitted to camshafts, so it is essential that they are heated evenly to a precise temperature for fitting to the camshaft. Overheating will result in premature failure.

Front 5

How must crankshafts be rotated?

Back 5

Camshafts may be rotated either with, or oppositely to, the direction of engine rotation.

Front 6

What kind of gears can camshaft gears use?

Back 6

Camshaft gears may use spur or helical cut gear teeth.

Front 7

What is a benefit and drawback of helical gears?

Back 7

Thrust loads are much higher when helical gears are used but they are much quieter in operation.

Front 8

How must gear backlash be measured?

Back 8

Gear backlash must be measured using thickness gauges or dial indicators.

Front 9

How can cam lift on block located camshafts be inspected?

Back 9

Cam lift on block located camshafts may be inspected using a dial indicator mounted above the push tube or rod.

Front 10

What is cam base circle or IBC?

Back 10

Cam base circle or IBC is that portion of the cam periphery with the smallest radial dimension.

Front 11

What is cam OBC?

Back 11

Cam OBC is that portion of the cam periphery with the largest radial dimension.

Front 12

How can critical cam dimensions be checked on an overhead camshaft or an out-of-engine camshaft?

Back 12

The critical cam dimensions may be checked on an overhead camshaft or an out-of-engine camshaft with a micrometer.

Front 13

How can cam lift be checked in a block-mounted camshaft?

Back 13

Cam lift can be checked with a dial indicator in a block-mounted camshaft.

Front 14

How should you be able to identify most cam failures?

Back 14

A visual inspection of the camshaft should identify most cam failures.

Front 15

How do you check profile wear on a camshaft?

Back 15

Profile wear may be checked to specification using a straightedge and thickness gauges. The camshaft should be mounted in V-blocks to test for straightness.

Front 16

How should out-of-engine camshafts be supported?

Back 16

Out-of-engine camshafts should be supported on pedestals, on V-blocks, or hung vertically to prevent damage.

Front 17

What type are most medium- and large-bore diesel engine cam followers?

Back 17

Most medium- and large-bore diesel engine cam followers are of the solid or roller types.

Front 18

In what applications are hydraulic lifters used in diesel engines?

Back 18

When hydraulic lifters are used in diesel engines, it is in small-bore applications.

Front 19

What does a cam train cost of?

Back 19

A cam train consists of the series of components it is responsible for actuating.

Front 20

What do the trains consist of used by most truck diesel engines with block-mounted camshafts?

Back 20

Most truck diesel engines with block-mounted camshafts use trains consisting of: a follower assembly, push tubes, and rockers.

Front 21

Where are OHCs used? When used, what is actuated indirectly by what?

Back 21

OHCs are used in many current diesel engines: when used, the injector and valvetrains are actuated indirectly using rocker arms.

Front 22

What are most valvetrains adjust with and what does that do?

Back 22

Most valvetrains are adjusted with a lash factor to allow for expansion of the materials as the engine heats to operating temperature.

Front 23

When are some injection pumping actuation trains set at zero lash or even a slight load?

Back 23

Some injection pumping actuation trains are set at zero lash or even a slight load when the actuating cam profile is on its IBC.

Front 24

Why may injector train settings be precisely set?

Back 24

Injector train settings may have to be precisely set because they help define injection timing.

Front 25

What do rocker assemblies do?

Back 25

Rocker assemblies provide a means of reversing the direction of linear movement of the push tube or follower and, in some cases, providing a mechanical advantage.

Front 26

What do cylinder head valves do?

Back 26

Cylinder head valves are used to aspirate or breathe the engine cylinders.

Front 27

What are cylinder head valves actuated by?

Back 27

They are actuated by the cam geometry and time the air into and end gases out of the engine cylinders.

Front 28

What are exhaust valves often manufactured with and why?

Back 28

Exhaust valves are often manufactured of more highly alloyed steels than intake valves because they must sustain much higher temperatures.

Front 29

When reconditioning valves by regrinding, a critical specification is what?

Back 29

When reconditioning valves by regrinding, a critical specification is the valve margin.

Front 30

How many diesel engines use an interference angle to seat valves and why?

Back 30

Most diesel engines do not use an interference angle to seat valves because the seating contact surface area is compromised.

Front 31

How do the seating force and gas flow of a 45-degree cut valve and 30-degree cut valve compare?

Back 31

A 45-degree cut valve has higher seating force but lower gas flow than a 30-degree cut valve.

Front 32

How are valve seats usually fit to the cylinder head? How do they related to the valve guide bore?

Back 32

Valve seats are usually interference fit to the cylinder head and finish ground concentric to the valve guide bore.

Front 33

When setting valve lash, the OEM specifications as to engine position for the valve being adjusted should be observed why?

Back 33

When setting valve lash, the OEM specifications as to engine position for the valve being adjusted should be observed because the cam geometry on some engines is not clearly divisible into IBC and OBC sections.

Front 34

How should valve lash be set? How are valves in current engines set?

Back 34

Valve lash should be set using thickness gauges; valves in current engines are set statically and cold.

Front 35

What do loose valves cause? What may result?

Back 35

Loose valves cause lower cylinder breathing efficiencies and what is known as top end clatter and may damage cam profiles.

Front 36

What doesn’t usually have to be adjusted as part of a routine valve adjustment? What is important about it that must be done and why?

Back 36

Valve yokes or bridges do not usually have to be adjusted as part of a routine valve adjustment: It is important that the bridge is properly supported to prevent its pedestal guide from being damaged.

Front 37

What is variable valve timing used for?

Back 37

Variable valve timing is commonly used to control exhaust valves for engine braking and also to delay intake valve closing for purposes of reducing emissions.

Front 38

What is creating a valve polar diagram?

Back 38

Creating a valve polar diagram is an effective way to map the valve opening and closing events in any engine you choose: You can also map how mechanically actuated injectors are phased into the cycle.