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Bearings & LubricationBearings & Lubrication

Roger BortignonRoger Bortignon

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FrictionFriction

FrictionFriction is… is…

the resistance opposing any effort to roll or slide one the resistance opposing any effort to roll or slide one object over anotherobject over another

 

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Causes of FrictionCauses of Friction

• minute minute imperfectionsimperfections on surface on surface interactinteract

• deformationdeformation or or indentationindentation of one of one object into anotherobject into another

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Kinds of FrictionKinds of Friction

1) 1) Fluid frictionFluid friction:: is less than solid friction but is less than solid friction but

it existsit exists

2) 2) Static frictionStatic friction: resistance to movement : resistance to movement

between 2 bodies in contact & at restbetween 2 bodies in contact & at rest

3)3) Kinetic FrictionKinetic Friction::

a)a) Sliding frictionSliding friction: resistance to continued : resistance to continued

movement once set in motionmovement once set in motion

b)b) Rolling FrictionRolling Friction: one body rolling over : one body rolling over

another – the least of the 3 frictionsanother – the least of the 3 frictions

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BearingsBearings

• Purpose of a bearing:Purpose of a bearing:

1)1) reduce frictionreduce friction

2)2) support a load/rotating shaftsupport a load/rotating shaft

a)a) radial radial

a)a) axial axial

• Bearing classifications:Bearing classifications:

1)1) friction bearings (aka: plain bearings)friction bearings (aka: plain bearings)

2)2) anti-friction bearingsanti-friction bearings

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Friction BearingsFriction Bearings

• 3 types of 3 types of friction bearingsfriction bearings……

1)1) JournalJournal bearing: crankshaft, piston pin, camshaft bearing: crankshaft, piston pin, camshaft

2)2) GuideGuide bearing: valve guide bearing: valve guide

3)3) ThrustThrust bearing: bearing:

• controls crankshaft end thrustcontrols crankshaft end thrust

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Friction BearingsFriction Bearings

• small 4 cycle engines use the engine parts as the wear small 4 cycle engines use the engine parts as the wear surfacessurfaces crankshaft connects directly to the connecting rodcrankshaft connects directly to the connecting rod camshaft spins directly in the engine blockcamshaft spins directly in the engine block

• larger engines use replaceable wear surfaces called…larger engines use replaceable wear surfaces called… precision insert bearingsprecision insert bearings

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Friction bearing advantages…Friction bearing advantages…

• physically compactphysically compact

• high speed (rpm) capabilityhigh speed (rpm) capability

• low costlow cost

• easily replacedeasily replaced

• can tolerate greater levels of debris in the lubricant can tolerate greater levels of debris in the lubricant

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2 categories of 2 categories of anti-frictionanti-friction bearings… bearings…

1)1) cylindrical roller cylindrical roller bearings (a) bearings (a)• used in radial & axial load applicationsused in radial & axial load applications• needle type (a) & tapered rollers (b) are needle type (a) & tapered rollers (b) are

variations of cylindrical rollers variations of cylindrical rollers

2)2) ball ball bearings bearings• are designed for radial loads & sometimes are designed for radial loads & sometimes

limited axiallimited axial• offer lower friction levels than #1offer lower friction levels than #1

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b

c

a

Bearing SurfacesBearing Surfaces

• the rolling elements in a bearing roll on bearing races…the rolling elements in a bearing roll on bearing races…

• rolling elements are made from high-carbon rolling elements are made from high-carbon chromium chromium steelsteel which also contains small amounts of which also contains small amounts of manganesemanganese and and siliconsilicon

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inner race

outer race

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More anti-friction bearings…More anti-friction bearings…

• ball thrust bearingsball thrust bearings

• needle thrust bearingsneedle thrust bearings

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How do bearings reduce friction?How do bearings reduce friction?

• chief cause of rolling friction: deformationchief cause of rolling friction: deformation

steel wheel on steel rail: .002 Coefficient of Frictionsteel wheel on steel rail: .002 Coefficient of Friction

riding a bike with a flat tire: very high Coefficient of Frictionriding a bike with a flat tire: very high Coefficient of Friction

this is why bearings surfaces are hardthis is why bearings surfaces are hard

• bearings & their races are very hard bearings & their races are very hard

smaller “footprint” & a lower Coefficient of Frictionsmaller “footprint” & a lower Coefficient of Friction

• this is a compromise between size & strengththis is a compromise between size & strength

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Lubrication - OilLubrication - Oil

Lubricating oil is designed to…Lubricating oil is designed to…

LubricateLubricate moving parts (minimize wear/reduce friction) by moving parts (minimize wear/reduce friction) by separating the two moving partsseparating the two moving parts

Engine oil is also designed to…Engine oil is also designed to…

Cool Cool engine parts by absorbing heatengine parts by absorbing heat

CleanClean engine via detergents that are added to the oil engine via detergents that are added to the oil

SealsSeals the area between the rings and the cylinder wall to the area between the rings and the cylinder wall to improve combustionimprove combustion

QuietsQuiets the engine by separating moving parts the engine by separating moving parts

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Engine OilEngine Oil

• Oil viscosityOil viscosity: its resistance to flow or rate of : its resistance to flow or rate of flow.flow.

• Low viscosity oil = thinner (think baby oil)Low viscosity oil = thinner (think baby oil)• High viscosity oil = thicker (think honey)High viscosity oil = thicker (think honey)

• Viscosity GradeViscosity Grade: determined by…: determined by…• Society of Automotive Engineers (SAE)Society of Automotive Engineers (SAE)• lower numbers = thinner oillower numbers = thinner oil• higher numbers = thicker oilhigher numbers = thicker oil

• Oil Service ClassificationOil Service Classification: determined by the : determined by the American Petroleum Institute (API)American Petroleum Institute (API) refer to handoutrefer to handout

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Synthetic (man-made) Engine OilsSynthetic (man-made) Engine Oils

1) Synthetic motor oils will withstand higher enginetemperatures than petroleum based oils

600°F compared to… 450°F for petroleum oils

2) Synthetic oils will begin lubricating at lowertemperatures than petroleum oils

-58°F degrees, compared to… -35°F degrees for petroleum based oils

3) Synthetic oils are more “slippery” than petroleum oils less wear and tear cooler engine better performance

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Lubrication SystemsLubrication Systems

1)1) Splash LubricationSplash Lubrication::

• used with a “dipper” (horizontal shaft)used with a “dipper” (horizontal shaft)

• or “oil slinger” (vertical shaft)or “oil slinger” (vertical shaft)

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Splash Lubrication Systems ContinuedSplash Lubrication Systems Continued

2) Barrel pump – common on many vertical shaft engines2) Barrel pump – common on many vertical shaft engines

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Full Pressure Lubrication SystemFull Pressure Lubrication System

• uses a positive displacement oil pumpuses a positive displacement oil pump• pump feeds pressurized oil to bearing surfaces, camshaft, pump feeds pressurized oil to bearing surfaces, camshaft,

connecting rod and valve trainconnecting rod and valve train• can be used in combination with splash systemcan be used in combination with splash system

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Oil FiltrationOil Filtration

3) Full Flow System3) Full Flow System

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Lubrication - GreaseLubrication - Grease

• grease is oil that has a thickener added to increase its viscositygrease is oil that has a thickener added to increase its viscosity lithium is often the thickenerlithium is often the thickener

• rust and corrosion additives are addedrust and corrosion additives are added• ““tackifiers” may it cling better to partstackifiers” may it cling better to parts• antifriction additives such as Molybdenum may be incorporatedantifriction additives such as Molybdenum may be incorporated• easier to seal in (and prevent leaks) than oil iseasier to seal in (and prevent leaks) than oil is• better than oils under heavy loadsbetter than oils under heavy loads• it is designed to remain in contact with parts and lubricate as wellit is designed to remain in contact with parts and lubricate as well

without being squeezed out between moving partswithout being squeezed out between moving parts or forced out from gravity or centrifugal forceor forced out from gravity or centrifugal force

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• NNational ational LLubricating ubricating GGrease rease IInstitute nstitute NLGINLGI

NLGI Grade Appearance Consistency food analog

000 fluid cooking oil

00 fluid applesauce

0 very soft mustard

1 soft tomato paste

2 moderately soft peanut butter

3 semi-fluid vegetable shortening

4 semi-hard frozen yogurt

5 hard smooth pate

6 very hard cheddar cheese spread

Wheel Bearing Grease