Mazda Training manual — part 254

7 – GLOSSARY

101

Piston Engine Fundamentals

TC010-05-01S

exhaust stroke

— the part of the four-

stroke cycle in which the piston moves up
into the cylinder, pushing burned gases out
through the exhaust valve.

exhaust valve

— lets burned gases out of

the cylinder.

face

— See valve face.

fan

— pulls cool outside air over the

radiator surface to pick up heat from the
coolant.

filter element

— the paper material in an

oil filter that screens out dirt and debris.

flex-blade fan

— a radiator fan that

flattens out as its speed increases.

float

— See valve “float.”

flywheel

— a heavy, round metal plate

attached to the crankshaft; the flywheel
keeps the crankshaft turning smoothly.

four-stroke cycle

— in most piston

engines, the set of piston movements that
produce power through combustion;
includes the intake, compression, power,
and exhaust strokes.

full-flow oil filter

— an oil filter that filters

all the oil pumped by the oil pump.

gear-driven camshaft with friction gear
— a camshaft drive in which a timing belt
drives one camshaft on each head; the
other camshaft on each head is driven by
helical gears and a friction gear.

gear-type pump

— a pump that uses two

gears, turning in opposite directions, to
pressurize liquid.

harmonic balancer

— See vibration

damper.

head

— See cylinder head, piston head, or

valve head

.

head gasket

— See cylinder head gasket.

hydraulic lash adjuster

— a component

mounted above the valve that uses
hydraulic pressure to automatically adjust
the valve clearance to 0; abbreviated as
HLA

.

impeller-type pump

— a pump that uses

a vane or rotor and centrifugal action to
pressurize liquid; most water pumps are
impeller-type pumps.

in-line

— an engine design with the

cylinders arranged in a single row.

insert bearings

— smooth surfaces fitted

into the support surfaces on the bottom of
the cylinder block; the crankshaft main
journals are supported by insert bearings.

intake stroke

— the part of the four-

stroke cycle where the piston moves down
in the cylinder, creating a partial vacuum
that sucks the air-fuel mixture through the
intake valve into the cylinder.

intake valve

— lets the air-fuel mixture

into the cylinder.

jiggle pin

— a thermostat component that

allows air in the cooling system to escape.

journal

— a smooth round surface on a

shaft that allows the shaft to turn freely.

keeper

— small, semi-circular metal parts

that fit in a groove at the end of the valve
stem to hold the valve spring in place.

lash

— See valve clearance.

7 – GLOSSARY

102

Piston Engine Fundamentals

TC010-05-01S

lifter

— the component in an overhead

valve engine that transfers the rotary
motion of the camshaft into the
up-and-down motion of the pushrod.

long block

— See partial engine.

lubrication system

— the engine

components that distribute oil to moving
parts to reduce heat and wear.

main bearing

— a split circular sleeve that

wraps around a crankshaft main journal; the
upper bearing fits into a main support on
the bottom of the cylinder block; the lower
bearing fits into a bearing cap.

main bearing journal

— a smooth round

surface on the crankshaft that supports the
crankshaft in the crankcase and allows it to
turn freely.

main gallery

— the largest oil passage in

the cylinder block.

margin

— the extra material on a valve

head behind the valve face that can be
ground to form a new face finish so the
valve can be reused after wearing.

mechanical fan drive

— a radiator fan

drive that uses a pulley and belt to drive
the fan.

mushroom valve

— See valve.

non-positive displacement pump

— a

pump that does not have to pump out all
the liquid that enters it; most water pumps
are non-positive displacement types.

offset piston

— a piston with the piston

pin bore drilled slightly away from the
center of the piston; offset pistons reduce
piston slap.

OHC

— See overhead cam.

OHV

— See overhead valve.

oil filter

— traps small particles of metal,

dirt, and debris carried by the oil so they
don’t recirculate through the engine.

oil pan

— a pan bolted to the engine under

the crankcase that serves as a holding
area for engine oil.

oil pick-up

— See strainer.

oil pressure indicator

— a gauge or

warning light on the instrument panel that
shows when the lubrication system cannot
supply all the oil needed by the engine.

oil pump

— provides the “push” to

circulate pressurized oil throughout the
engine.

oil ring

— three pieces, or segments,

mounted below the compression rings on
the piston that scrape oil from the cylinder
wall and direct it into the open space inside
the piston skirt; the oil ring typically
includes two scraper rings and an
expander ring.

oil seals

— installed at various points in

the engine to prevent oil from leaking out of
the engine or into places where oil should
not be present.

overflow tube

— a cooling system

component that allows coolant to escape if
the cooling system is overfilled or if the
engine is overheating.

overhead cam

— an engine design with

the camshaft and the valves mounted
above the cylinders; the camshaft directly
operates the valves; abbreviated as OHC.

overhead valve

— an engine design with

the valves mounted above the cylinders;
the camshaft, located in the engine block,
operates each valve through a pushrod
and rocker arm; abbreviated as OHV.

7 – GLOSSARY

103

Piston Engine Fundamentals

TC010-05-01S

partial engine

— a short block plus

cylinder head(s) and cover(s), timing belt
and covers, and oil pan.

piston “slap”

— the sound made by a

piston as it hits the cylinder wall during the
power stroke.

piston

— forms the bottom of the

combustion chamber and receives the
energy created by combustion; pistons
move up and down in the cylinders.

piston head

— the top surface of a piston.

piston pin

— a steel pin (also called a

wrist pin) that attaches the piston to the
connecting rod.

piston pin bore

— a cylindrical hole drilled

through the piston; the piston pin is inserted
through the piston pin bore.

piston rings

— rings mounted on the

piston to seal the combustion chamber,
scrape oil from the cylinder walls, and
carry heat from the piston to the cylinder
walls.

positive displacement pump

— a pump

that pumps out all the liquid that enters it;
liquid is not allowed to circulate inside a
positive displacement pump; most oil
pumps are positive displacement types.

power stroke

— the part of the four-

stroke cycle where a spark from the spark
plug ignites the air-fuel mixture, creating
very high pressure on top of the piston,
which is pushed down in the cylinder and
turns the crankshaft.

pressure cap

— screws onto the radiator

filler neck and maintains pressure in the
cooling system to raise the boiling
temperature of the coolant.

pressure relief valve

— an oil pump

component that allows oil to be diverted
from the pump when maximum oil pressure
has been reached.

pressure valve

— a spring-loaded valve in

the radiator pressure cap that allows steam
and coolant to escape to the radiator
reservoir when high pressure builds in the
cooling system.

pushrod

— a component in an overhead

valve engine that transfers motion from the
lifter to the rocker arm, which opens and
closes the valve.

radiator

— the part of the cooling system

that dissipates the heat the coolant has
absorbed from the engine.

radiator reservoir

— holds coolant that

flows from the radiator when the engine is
very hot; when the engine cools, the
coolant in the reservoir is drawn back into
the cooling system.

retainer

— See valve retainer.

rocker arm

— a valve train component

that pushes down on the valve spring,
allowing the valve to open; the rocker arm
is moved by a pushrod or camshaft.

rocker arm shaft

— a hollow shaft used to

mount shaft-pivoted rocker arms.

rotor-type pump

— a pump that uses two

rotors, one turning inside the other, to
pressurize liquid; most oil pumps are rotor-
type pumps, also called trochoid pumps.

seat

— See valve seat.

short block

— describes the cylinder

block, crankshaft, bearings, connecting
rods, and pistons as a unit.

7 – GLOSSARY

104

Piston Engine Fundamentals

TC010-05-01S

skirt

— the lower part of the piston, from

below the piston rings to the bottom of the

piston.

spark plug

— produces a spark to ignite

the air-fuel mixture in the cylinder.

spring seat

— washer-like parts that hold

the valve spring in place.

strainer

— a component in the oil pan that

draws oil from the pan for circulation

throughout the engine; screens out large

pieces of debris in the oil.

stroke

— the length of piston travel

between top dead center and bottom dead

center, usually expressed in millimeters.

tappet

— See lifter.

tappet clearance

— See valve clearance.

TDC

— See top dead center.

tensioner pulley

— a pulley that maintains

timing belt tension and prevents the timing

belt from slipping.

thermostat

— restricts the flow of coolant

until the engine reaches its operating

temperature.

thermoswitch

— an electrical component

that senses the coolant temperature and

activates an electric motor for the radiator

fan.

thrust bearing

— a special bearing that

matches up with a thrust surface on the

crankshaft to control front-to-rear

movement of the crankshaft.

ticking

— See valve “ticking.”

timing belt

— a belt connecting the

crankshaft pulley to the camshaft pulley(s)

used to drive the camshaft(s).

timing chain

— a chain connecting the

crankshaft gear to the camshaft gear used

to drive the camshaft.

top dead center

— the position of a

piston at its highest point in the cylinder;

abbreviated as TDC.

torque

— turning or twisting effort.

torsional vibration

— the constant

twisting and untwisting of the crankshaft

caused by the downward thrust of the

pistons.

trochoid pump

— See rotor-type pump.

V-6

— an engine design in which the

cylinders are grouped into two banks of

three cylinders each, arranged in a “V”

pattern.

V-8

— an engine design in which the

cylinders are grouped into two banks of

four cylinders each, arranged in a “V”

pattern.

vacuum valve

— a spring-loaded valve

in the radiator pressure cap that allows

coolant to return to the radiator when the

engine cools.

valve “float”

— the failure of a valve to

seat at high speed, usually caused by a

weak valve spring.

valve “ticking”

— a noise created when

the valve train parts hammer against each

other, usually because the valve clearance

is too large; an HLA noise caused by dirt or

air trapped in the HLA.

valve

— seals against a seat in the cylinder

head and opens and closes at precise

intervals to allow the air-fuel mixture into

the cylinder or exhaust gases out of the

cylinder.