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.