Engines - Cylinder Head and Valve Train Flashcards
This engine component is a lobed shaft that changes rotary motion into reciprocating motion.
the camshaft
This engine component controls the opening and closing of the intake and exhaust valves, and may also be used to control the fuel injection, gas admission, or air start.
the camshaft
What is the main function of an engines camshaft?
to control the opening and closing of the intake and exhaust valves
With this cam arrangement, the cam pushes on the lifter and push rod, which causes the rocker arm to change direction, which opens the valve.
cam in block (pushrod) arrangement
With this cam arrangement, the cam pushes directly on the valve.
overhead cam arrangement
What four things do the shape and position of the lobes in the cam determine in an engine?
- firing order
- amount of lift
- duration of the cam
- valve overlap
On a camshaft, what is the duration of the cam?
the length of time in degrees of crankshaft rotation that the valve is open
With a camshaft, when the pushrod is on the nose of the cam, the valve is:
fully open
With a camshaft, when the pushrod is on the base circle of the cam, the valve is:
fully closed
With a camshaft, when the pushrod is on the ramp of the cam, what is happened?
the valve is either opening or closing
What does the ramp of a cam on a camshaft determine?
the length of time it takes to open and close the valve
What are the three basic methods of construction for camshafts?
- cast iron and ground to the desired profile
- machined to profile from steel billet
- assembled from individual components
The speed of a camshaft on a four-stroke engine is _______ the crankshaft speed.
1/2
To achieve the drive ratio required by the camshaft on a four stroke engine, the cam shaft gear would have ________ the number of teeth as the crankshaft gear.
twice
True or false:
Two-stroke engines never have camshafts.
false;
they rarely have camshafts
*some two-stroke diesels have camshafts to operate exhaust valves, some mechanical fuel ignition, or gas admission valves
True or false:
Camshafts may be driven through a gear train with timing marks, roller or silent chain or a timing belt.
true
In a four-stroke engine, when one piston is travelling towards TDC in the compression stroke, what stroke will its running mate be in?
exhaust
In a four-stroke engine, when one piston is travelling towards BDC in the power stroke, what stroke will its running mate be in?
intake
In a four stroke engine, what do the amount of intake lead degrees and exhaust lag degrees indicate?
the valve overlap
The purpose of this engine component is to transfer motion to the push rod.
lifters
What are the three common types of lifters found in engines?
- hinged roller
- roller
- mushroom
In an engine, what is a tappet?
a cam lifter
How is oil supplied to the rocker arms in an engine?
through a metering valve in the lifter, through the pushrod and up to the rocker arm
What type of engine lifter arrangement requires periodic adjustment of the valve lash?
solid type lifters
What type of engine lifter arrangement does not need the valve lash to be adjusted (self-adjusting)?
hydraulic lifters
What type of engines are hydraulic lifter most often found on?
automotive and large stationary engines
When running hydraulic lifters in an engine, what does a tapping noise generated by the lifters indicate?
the lifter is worn internally;
it must be replaced
What two measurements are required to calculate the lift of a cam on a camshaft?
- the base circle diameter (A)
- the base circle to the nose (B)
Why is it important to return parts back to where they came from on engines during reassembly?
they will have developed a unique wear pattern;
installing them into other places can result in increased wear and premature failure
True or false:
On flat bottom lifters, if there is any pitting on the flat bottom lifters, or if the bottom is slightly concave, do not reuse the lifter.
true
True or false:
On roller lifters, if there is pitting or chipping on the rollers, or excessive clearance on pivot points or roller bearings, do not reuse the lifter.
true
What are four things that can result from incorrect camshaft timing?
- altered valve opening and closing points
- poor engine performance
- damage to engine components (interference engines)
- altered fuel injection timing on engine with camshaft actuated injectors
This engine component serves as a link between the lifter and the rocker arm in a camshaft-in-block engine.
pushrods
What three things need to be inspected on a pushrod?
- straightness
- blockage in the oil port
- wear on the ends
This engine component is the mechanical linkage between the pushrod and the valve.
rocker arm
This engine component changes the upward motion of the lifter and pushrod into a downward motion of the valve.
rocker arm
With a cam-in-block engine, where is the valve lash set?
at the rocker arm
This engine component is used on cylinder heads with four valves per cylinder, and allows one rocker arm to open both valves simultaneously.
valve bridges
Valve bridges are also known as:
crossheads
True or false:
Engines may use one cylinder head for all the cylinders, one head for several cylinders, or one head per cylinder.
true
What component of an engine contains the combustion chamber?
the cylinder head
What component of an engine contains the valves and ports which route the flow of the inlet air/fuel mixture and exhaust gases?
the cylinder head
In an engine, what are the intake and exhaust manifold connected to?
the cylinder head
On an engine valve, what is the valve margin?
the flat edge around the OD of the valve
- Which type of engine valve is made of a better material: the intake of exhaust valve?
- Why is this?
- exhaust valve
- operates at higher temperatures and in the presence of corrosive gasses
Where does approximately 75% of the valve cooling occur on engine valves?
between the valve face and valve seat
*in sodium valves, the heat transfer is 50% / 50% ⟶ the sodium core carries more heat into the valve stem
Where does approximately 25% of the valve cooling occur on engine valves?
between the valve stem and valve guide
*in sodium valves, the heat transfer is 50% / 50% ⟶ the sodium core carries more heat into the valve stem
This engine component is responsible for closing the valves and keeping them firmly against the valve seat to ensure a positive seal and good heat transfer.
valve springs
This engine component is locked in a groove on the valve stem and secures the valve, spring, and washer together.
valve retainers (valve keeper)
What is another name for valve retainers in engines?
valve keepers
This engine component is the sealing point between the valve face and the cylinder head casing, and may be part of the cylinder head or a removable insert.
valve seats
This engine component is usually located on the exhaust valve and causes the valve to turn slightly every time the valve actuates.
valve rotators
What component is used if carbon is likely to become deposited on an engine valve?
valve rotators
This engine component may be integral or removable, and supports and aligns the valve to keep it square with the valve seat.
valve guides
This engine component controls the lubrication of the valve guide and stem.
valve seals
What engine issue is indicated if there is blue smoke on initial acceleration?
leaking valve seals
What effect does an increased valve lash have on cooling?
valve lash ↑ = valve cooling ↑
*the increased valve lash allows the valve to stay in contact with the valve seat longer, allowing for better cooling
- Which valve usually has a larger valve lash: intake or exhaust valves?
- Why is this?
- exhaust
- larger thermal growth (due to hotter temperatures) and cooling;
the larger valve lash allows the valve face to stay in contact with the valve seat longer
What are the three biggest problem areas encountered when rebuilding cylinder heads?
- cracked or warped head surfaces
- valve and valve seat condition
- wear of the valve guides
When rebuilding an engine, how should the valve seals be checked for proper operation?
using a vacuum or solvent leak test
What issues does insufficient valve clearance cause within an engine?
overheated/burnt valves;
the valve is held slightly open, resulting in poor heat transfer
What valve lash issue could eventually cause the valve or pushrod tip to break off?
excessive valve lash;
the valve will open and close hard, resulting in increased shock loading
What are three components that should be replaced during an engine cylinder head rebuild?
- valve guides
- valves
- valve seats
- What component needs to be replaced first when reconditioning a cylinder head?
- Why is this?
- the valve guides
- the valve seats use the valve guides as a pilot hole
What type of fit is required on a valve guides in relation to the bore that holds them?
interference fit
What happens if the valve stem is nicked when grinding the valve face back into tolerance?
the valve stem will break during operation;
this must be avoided
While reconditioning a cylinder head, it has been determined that the valve seat must be replaced. What are three methods to remove the valve seat insert?
- specific insert puller
- special heeled chisel
- welded bead on the ID
When touching up an engine valve seat, commonly a _____º and _____º stone is used to relieve the upper and lower valve seat edges to attain the correct contact width of the valve.
15º and 60º
This is after the inital 45º angle has been ground into the valve seat.
When checking engine valve contact with Prussian blue, why is it important to not rotate the valve?
this will result in an inaccurate reading
When reconditioning a cylinder head valve, what happens if the seat is too wide?
too much contact area = carbon build up and potential leakage
When recondition a cylinder head valve, what happens if the seat is too narrow?
less contact area = poor cooling and accelerated wear
On a push rod engine, which of the following components contacts the rocker arm?
the pushrod
How is the valve lift determined in an engine?
By the height of the nose or lobe
True or false:
Valve guides need to be repaired or replaced before valve seats are repaired or replaced because it ensures correct alignment between the guide and seat.
true
True or false:
Cylinder head bolts should be torqued in three stages at least, starting with the outer fasteners first, then finishing with the middle fasteners.
false;
always start with the middle fasteners and work outwards to avoid distortion
Which stage of engine cycle should the first cylinder be in, when checking for inlet and exhaust valve clearances?
compression
What are the two main reasons for valve lash in an engine?
- to allow thermal expansion of valve train
- To compensate for wear of valve train components
True or false:
Valve lash = valve clearance.
true
What effect would wear on the rocker arms or pushrods have on valve lash?
it would increase valve lash
What effect would wear on the valve seat have on valve lash?
it would decrease valve lash
How should the engine be orientated in order to set the valve lash?
piston #1 needs to be at TDC on the compression stroke;
this can be verified with an aluminum rod through the spark plug hole or with timing marks on the dampener or flywheel
In engines, why is exhaust valve clearance normally greater than intake valve clearance?
to allow for greater expansion of the components during operation
True or false:
Excessive engine valve clearance causes poor engine performance and noisy valve train.
true
True or false:
Insufficient engine valve clearance causes poor engine performance and damage to valve train components.
true;
burnt valves from poor cooling
When checking the valve lash in an engine, how should the rockers be when the cylinder in the compression stroke?
both the intake and exhaust rockers should be loose
When checking valve lash in an engine, how should the rockers be when the cylinder is in overlap?
both rockers should be locked against the valves
Identify the four components in a valve train.
- camshaft
- lifter
- pushrod
- rocker arm
What keeps the camshaft timed with the crankshaft?
gears, chains or timing belts
True or false:
Pushrods may have hollow tubes with oil galleries so oil can be sent to the cylinder head.
true
Depending on the engine design, the cylinder head may cover:
- on cylinder
- four cylinders
- six cylinders
- all of the above
- all of the above
Explain the purpose of cylinder head ports?
direct flow into and out of the cylinder
What are the three main functions of the cylinder head?
- retains the gasket seal between the block and head
- contains combustion chamber, valves, and oil and coolant galleries
- housing manifolds and injectors, air start and gas admission valves
List the two main functions of engine valves.
- seals the cylinder during compression and power stroke
- permits air/fuel mixture on intake and removes combustion gases on exhaust
When compared to an integral vale seat, valve seat inserts provide a replaceable wear surface with improved:
wear characteristics
Valve seals control valve guide and stem lubrication to prevent:
oil consumption
Before removing the cylinder head from a locked out and purged engine, you must do what task first?
drain the coolant and oil
What must be done after replacing valves and valve seat inserts?
check the valve face and valve seat contact
When does the exhaust lead happen on a four-stroke engine?
at the end of the power stroke, before BDC
When does the intake lag happen on a four-stroke engine?
after BDC on the intake stroke, before starting the compression stroke
How many angles do valve seat commonly have ground into them?
Three
First is 45º, followed by a 15º and 60º angle.
What determines the amount of lift produced by a cam?
The distance from the base circle to the nose
Which tools are commonly used to check dimensions on Valve guides?
Hole gauge and outside micrometer
What is the ratio of the number of gear teeth on a camshaft drive gear vs the number of teeth on the crankshaft gear in a four stroke engine?
2:1
Remember that the camshaft turns at half the speed of the crankshaft.
What is the first angle to be ground into a valve seat?
45°
This is followed by a 15º and then 60º
