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Engine Service and Repair > 190201h > Flashcards

190201h Flashcards

1
Q

On engines with UNIT fuel injectors the cam also actuates

A

the injector operating mechanism

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2
Q

the cam is driven by the crank and changes motion from what to what?

A

rotary motion into reciprocating

Cam to followers

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3
Q

Cam nose is a mounting surface for the drive gear or sprocket. What maintains alignment of the gear to cam

A

a keyway is machined into the nose to retain the key

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4
Q

What are the load bearing surfaces of the cam

A

Journals. they support the cam in the block

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5
Q

Lobes are eccentrics that convert the rotary motion of the cam to…

A

reciprocating motion of the cam follower

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6
Q

depending on the engine, the cam gear train may also run the

A

fuel injection pump, fuel transfer pump, oil pump , tach

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7
Q

what is a helical gear machined into a cam most likely to run?

A

oil pump or tach

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8
Q

the nose on a cam lobe is…

A

the point of maximum lift

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9
Q

the centerline is the

A

point between opening and closing ramps

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10
Q

what part of the lobe does a lifter ride up and down on?

A

the opening and closing ramps. there is one on all lobes

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11
Q

what is the base circle

A

the base diameter of the lobe and no valve is open on it

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12
Q

what math formula on what parts gives you calculated lift?

A

subtract base circle from the lobe height

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13
Q

What is the definition of “Duration”

A

the number of degrees between where the valve opens to the point where it closes

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14
Q

What are the three ways camshafts are manufactured

A

Casting, machine or forged from alloyed steel and assembled from components

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15
Q

Why are cast camshafts heat treated

A

To improve durability

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16
Q

When new most camshafts have a black coating on the lobes. What is it?

A

Pressure resistant antiwear agents molybdenum disulfide or manganese phosphate

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17
Q

Where would you use a steel camshaft

A

Where extreme loads are placed on the camshaft such as with unit fuel injectors

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18
Q

Why would you use a modular camshaft

A

In some large displacement diesel engines or to permit ease of manufacturing and service

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19
Q

What are the two general camshaft locations

A

In block or overhead

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20
Q

Camshaft motion is transmitted how with the in block design

A

Through the cam follower and pushrod to the rocker arm

21
Q

What are the advantage of the overhead camshaft

A

Fewer moving parts, less friction, more accurate valve timing

22
Q

What type of bushings are generally used to support the camshaft and control and play

A

Friction type bearings

23
Q

How are bushings normally retained in the cylinder block

A

Bushings are retained by a press fit in the cylinder block cam bearing bores

24
Q

Many diesels with overhead camshaft use what type of bearings

A

Shell type bearings. Which permits the camshaft to be removed vertically from the cylinder head

25
Q

True or false. The camshaft is one of the last components to receive oil

A

True

26
Q

What are three different ways to limit end play of the camshaft

A

Taper of the camshaft lobes. Cam shaft driven by helical gears. A thrust plate or washer is the most common method of controlling and play on diesel engine camshafts

27
Q

What two ways are camshaft lobes lubricated by oil

A

Sprayed out of the camshaft bearing and splashed off the valve operating mechanism

28
Q

What’s the purpose of a cam follower

A

Turn the rotary motion of the camshaft into reciprocating motion by following the profile of the cam lobe

29
Q

What are the three basic types of cam followers

A

Solid, roller and hydraulic

30
Q

What are two other names for cam followers

A

Lifters or tappets

31
Q

What are two types of flat faced solid lifters

A

Straight body and mushroom

32
Q

What is the advantage of a mushroom type solid lifter over a straight body lifter

A

Mushroom type have a greater surface area in contact with the cam lobe and will therefore withstand higher contact pressure

33
Q

What are three ways a solid lifter is kept from wearing quickly

A

The lifter has a concave, the lobe has a taper, the lifter centerline is also offset in relation to the cam lobe creating rotation

34
Q

A solid cam follower has no mechanism to compensate for heat expansion therefore what must be in place

A

There must be some clearance or valve lash to allow for expansion as temperature increases

35
Q

Roller lifters can either be a solid or hydraulic design. What are three characteristics

A

The cam lobe for a lifter is ground flat and has no taper. The roller is usually centered on the cam lobe for Full Contact. It cannot turn during operation and will have a positioning mechanism to prevent it from turning

36
Q

Roller type cam followers reduce what three things

A

They reduce friction, wear, and sides thrust on the lifter body

37
Q

What are three advantages of roller type cam followers

A

Reduced frictional loss, can handle much higher operating loads, allow a quicker rate of valve opening and closing then solid cam followers

38
Q

Overhead cams have what built into the rocker arm

A

A cam follower roller

39
Q

What are two things a hinged roller eliminates

A

The need for lifter bores in the cylinder block and side thrust created by conventional roller followers

40
Q

What engine design uses the hinged roller

A

Primarily used on engines with mechanically actuated fuel injectors. It opens both valves and injectors

41
Q

What are the two advantages of hydraulic lifters over solid lifters

A

Hydraulic operated lifters compensate for heat expansion therefore no valve lash is necessary and hydraulic lifters operate with no valve clearance and all valvetrain components are in continual contact during engine operation resulting in less valvetrain noise

42
Q

What are two ways timing gears are installed on the camshaft and two ways that they are indexed

A

They are bolted or pressed on and indexed by a keyway or Dowe

43
Q

If the physical distance between crank and cam is too great what’s in between

A

An idler gear that does not affect speed relationship but does change direction of rotation

44
Q

Timing chains are used on both in block and overhead cam applications what are two types of chains

A

Silent type chain for light and medium duty and roller type chain for heavy duty applications

45
Q

On four stroke cams intake and exhaust lobes are offset. what is this referred to as

A

Lobe separation angle

46
Q

What is one of the most critical steps in reassembling an engine

A

Timing the camshaft

47
Q

Incorrect camshaft timing will result in what four things

A

Altered valve opening and closing points, poor engine performance, damage to engine components due to physical contact, alter fuel injection timing on engine camshaft actuated injectors

48
Q

What other engine accessories may the camshaft gear drive

A

Fuel injection pump,oil pump, water pump,accessory drives and balance shafts

49
Q

What may be used on the camshaft drive gear instead of multiple timing marks

A

Some engines use offset keys to change the camshaft timing

Engine Service and Repair (12 decks)

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