Parts, Bearings, Gearing Only]

8/9/2019 Parts, Bearings, Gearing Only]

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Engine Parts, Description, Function, Construction

Cylinder Barrel

Chrome-molybdenum or nickel-molybdenum steel

Used to guide and seal piston and to mount cylinder

assembly to head

Barrel threads into head to form cylinder assembly


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Cylinder interior wall

Cylinder Walls


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Cylinder Walls

Inside surface of cylinder barrel is honed to a

controlled amount of roughness Rough enough to hold oil film but smooth enough to

minimize friction and wear

Plain steel cylinder walls are not treated to preventwear or corrosion

Nitridedcylinder walls are hardened to reduce wear

but still rust as easily as plain steel walls. Nitridingis exposing the cylinder wall to ammonia at high

temperatures and it hardens the wall to a thickness of

approximately .005


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Chrome cylinder walls use

chromium plating to resist

wear and provide a

corrosion resistant surface.

Cylinders may be chromed

back to standard inside

dimensions if they become

worn

Chrome is too smooth to

hold oil without etching or

channeling during the

overhaul process


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Cylinder wall CHOKE

The cylinder wall istapered inward towards

the top so that as the

engine warms up, the

hotter top of the wall

expands more than the

bottom, creating a round

barrel at operating

temperature.


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Cylinder heads

Constructed of cast

aluminum Provides combustion

chamber, and mounting

areas for spark plugs andvalve parts


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The cylinder head is designed to transfer heat by

conduction to the fins and then from the fins to the

air by convection

The exhaust side of the head has the most fins as it

runs the hottest

The head also may incorporate a drain line fittingto allow excess oil to return to the crankcase

(intercylinder drain lines on radials)


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Valve Guides

Made of bronze

Secured in the head by aninterference (shrink) fit

Valve Seats

Made of chrome steel,

stellite, or brass

Secured by interference fit


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Crankcase

The crankcase holds all of the engine parts in

alignment and supports the cylinders and crankshaft

It provides a place to mount the engine to the

aircraft

Constructed of aluminum alloy

Divided into sections (radial)


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Nose section - Houses prop shaft and bearings

Power section - mount for cylinders

Fuel induction section - intake tubes, blower,

manifolds (supercharger)

Accessory section - mounts for magnetos, pumps,

generators (magnesium)


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Opposed crankcase Sections are not as distinct as in the radial and the

crankcase splits from front to rear instead of in

radial sections


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Pistons

Constructed of aluminum alloy

Parts include top, ring grooves, ring lands, skirt,

and piston pin boss

Cooling fins on the bottom help the oil carry heat

away from the piston top


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Cam ground pistons

diameter of the piston is greater perpendicular to

the piston pin boss

This compensates for uneven expansion during

operation (becomes round at operating temperature)


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Piston head designs


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Piston rings (general)

Provide seal between cylinder wall and piston

Rings ride on a thin film of oil

Conduct heat from the piston out to the cylinder

and the fins

Material is cast iron or chrome steel

Piston rings (type)

Compression rings are located at the top of thepiston and seal the combustion chamber

Types include rectangular, tapered,wedge


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Compression rings


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Oil control rings

On bottom of piston below compression rings

Regulates oil film thickness on cylinder wall

Holes in ring and piston allow excess oil to drain

back to crankcase

Too much oil film and the engine will use

excessive oil and too little oil causes heat and

insufficient lubrication

Oil scraper rings Directs the oil away from or towards the oil control

rings depending upon the requirements of the

engine


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Piston ring end gap

The gap at the end of the rings allows for expansion

and contraction and unevenness in the cylinder wall

Butt, step and angle types

Always stagger the end gaps during ring

installation to prevent losing compression


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Piston Pins (wrist pins)

Connects the piston to the end of the connectingrod

Constructed of hardened steel

The pin is retained in the piston with clips or plugsto prevent cylinder wall scoring

Typical Lycoming and Continental pins are free-

floating, meaning the pin is not secured to thepiston or the rod.


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Connecting Rod Assembly

The link between the crankshaft and the piston

Normally steel but some low powered engines use

aluminum to save weight Cross section is an H or I

Types include : Plain Rod

Fork and blade rodMaster and articulated


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Plain Type Rods

Used on inline and opposed engines

Small bushing at piston pin end is pressed in place

and reamed to final dimensions

Large end of rod includes a cap, bolts, nuts, and

plain bearing inserts

Rods are numbered as to cylinder and for cap-to-

rod alignment


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Fork and Blade Connecting Rod

Used on V type engines

One rod inside another allows cylinders to be

aligned and to share a common location on the

crankshaft


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Master and Articulating Rod

Used on radial engines

Uses knuckle pins to retain articulated rods to

master

Master Rod

Articulating Rod


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Master/Articulating Rod in Action


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Crankshaft Main Bearing Journal, Pin, Arm


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Crankshaft Ends For Mounting Propellers


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Dynamic Dampers can be mounted to the

crankshaft to reduce vibration (floating)

Counterweights are also used to reduce vibration

but they are rigid and do not float

Counterweights and dampers are used in piston

engines because the power pulses and movement of

the pistons create large amounts of vibration

Vibration shortens airframe and engine life and can

lead to premature component failure

The engine is also mounted in rubber bushings to

absorb vibration


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2 Piece Crankshaft With Counterweights

(Single Throw, Single Cylinder)


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Valves and the Valve System

Valves control the flow of gases inside the engine

Poppet valves are the most common and get their

name from the popping open and closed during

operation

Intake valves are chrome steel and are cooled by

the incoming air and fuel mixture

Exhaust valves are also alloy steel but are often

filled with metallic sodium for cooling. Valve

faces may be coated with Stellite to reduce wear

and corrosion

Valve faces are ground to 30 degrees for intake

(airflow) and 45 degrees (cooling) for exhaust


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1290 degrees F

(typical)


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Valve Springs

Inner and outer springs are used to prevent bounce,provide redundancy, and increase valve closing

pressure

Held in place by retainer washers on the top andbottom of the spring

Split key or keeper holds the retainers and

springs in place on the valve stem


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Valve Lifter or Tappet

May be solid, roller, or hydraulic

The lifter follows the cam lobes and pushes on the

pushrod

Solid and roller lifters require adjustable rocker

arms

Hydraulic type lifters fill with oil and lengthen to

compensate for any clearances in the valve system


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Camshaft

Turns at 1/2 the speed of the crankshaft

Must be mechanically coupled to the crankshaft for

timing purposes (gears, belts, chains)

The camshaft consists of bearing journals and lobes

spaced along the shaft

Each lobe is positioned to open and close a valve at

a specific time

Lobe


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Pushrod

transmits push of lifter up to rocker arm

Hollow to allow oil to flow to the top of the

cylinder for valve part lubrication

Length can be varied to adjust valve clearance

Valve clearance is the space between the top of the

valve stem and the rocker arm. This clearance is to

prevent a valve from being held open with the

resulting heat build-up and loss of compression

valve clearance increases as the engine operates

due to cylinder expansion (solid lifters)

Hydraulic lifters have a 0 clearance in operation


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Valve clearance adjustment

Valve clearance measurement


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Rocker Arm

Adjustable in solid lifter engines and fixed inengines with hydraulic lifters

One end rests on the valve stem and the other on

the pushrod

Rocking motion opens and closes the valves

Roller rocker arms incorporate a roller that reduces

friction and are used in some radials and

experimental engines


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Bearings

Must be able to withstand forces inside anengine with minimal friction and heat build-

up. Must accept radial and thrust loads

Plain Bearings

A steel insert with babbitt (lead alloy) bonded to

the bearing surface

Plain bearings are keyed to keep them in place

A lip or flange allows the plain bearing to accept

thrust loads

Commonly used as crankshaft and rod bearings in

opposed engines


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Roller Bearings (antifriction)


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Roller Bearings (antifriction)

Hard steel rollers captured between an innerand outer race and held in alignment by a

cage

May be tapered to absorb radial and thrustloads or straight to absorb radial loads only


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Parts of a Ball Bearing

OUTER RACE

INNER RACE

CAGE

BALL


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Ball Bearings (antifriction)

Used for both radial and thrust loads

Deep grooves in races allow thrust

loads


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Bearing cleaning and safety

Wash old grease and debris with solvent

Blow dry with shop air but do not spin the bearing

with the air blast

Reapply grease or oil immediately to prevent

corrosion Protect skin and eyes from solvent contact

ll d i G i


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Propeller Reduction Gearing

Purpose is to reduce propeller rpm to its optimal

speed and to increase engine rpm to its optimal

speed

Propeller always turns slower than the engine

Gear Ratios:

Expressed as 2:1, .64:1, 300:1

At what speed will the propeller be turning if theengine rpm is 2000 and the gear ratio is 2:1?

1000 rpm

Whi h d ti ti ill id th f t t


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Which reduction ratio will provide the fastest

propeller speed 10:1 or 4:1? 4:1 (it is the closest to 1:1)

Spur Gears

Simple drive and driven gear system

Number of teeth on gear and gear diameters

determine reduction ratio

Large gear would be mounted to propeller as it

turns the slowest

Planetary Gears


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Ring gear, Planet gear, Sun gear

Large gear reductions possible

Compact and versatile Common in large radials and turbine engines

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