Engine Parts, Description, Function, ConstructionCylinder Barrel

Chrome-molybdenum or nickel-molybdenum steelUsed to guide and seal piston and to mount cylinder assembly to headBarrel threads into head to form cylinder assembly

Engine Parts, Description, Function, ConstructionCylinder interior wallCylinder Walls

Engine Parts, Description, Function, ConstructionCylinder WallsInside surface of cylinder barrel is honed to a controlled amount of roughnessRough enough to hold oil film but smooth enough to minimize friction and wearPlain steel cylinder walls are not treated to prevent wear or corrosionNitrided cylinder walls are hardened to reduce wear but still rust as easily as plain steel walls. Nitriding is exposing the cylinder wall to ammonia at high temperatures and it hardens the wall to a thickness of approximately .005

Engine Parts, Description, Function, ConstructionChrome 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 wornChrome is too smooth to hold oil without etching or channeling during the overhaul process

Engine Parts, Description, Function, ConstructionCylinder wall CHOKEThe cylinder wall is tapered 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.

Engine Parts, Description, Function, ConstructionCylinder headsConstructed of cast aluminumProvides combustion chamber, and mounting areas for spark plugs and valve parts

Engine Parts, Description, Function, ConstructionThe cylinder head is designed to transfer heat by conduction to the fins and then from the fins to the air by convectionThe exhaust side of the head has the most fins as it runs the hottestThe head also may incorporate a drain line fitting to allow excess oil to return to the crankcase(intercylinder drain lines on radials)

Engine Parts, Description, Function, ConstructionValve GuidesMade of bronzeSecured in the head by an interference (shrink) fit

Valve SeatsMade of chrome steel, stellite, or brassSecured by interference fit

CrankcaseThe crankcase holds all of the engine parts in alignment and supports the cylinders and crankshaftIt provides a place to mount the engine to the aircraftConstructed of aluminum alloyDivided into sections (radial)

Nose section - Houses prop shaft and bearingsPower section - mount for cylindersFuel induction section - intake tubes, blower, manifolds (supercharger)Accessory section - mounts for magnetos, pumps, generators (magnesium)

Opposed crankcaseSections are not as distinct as in the radial and the crankcase splits from front to rear instead of in radial sections

PistonsConstructed of aluminum alloyParts include top, ring grooves, ring lands, skirt, and piston pin bossCooling fins on the bottom help the oil carry heat away from the piston top

Cam ground pistonsdiameter of the piston is greater perpendicular to the piston pin bossThis compensates for uneven expansion during operation (becomes round at operating temperature)

Piston head designs

Piston rings (general)Provide seal between cylinder wall and pistonRings ride on a thin film of oilConduct heat from the piston out to the cylinder and the finsMaterial is cast iron or chrome steel

Piston rings (type)Compression rings are located at the top of the piston and seal the combustion chamberTypes include rectangular, tapered,wedge

Compression rings

Oil control ringsOn bottom of piston below compression rings Regulates oil film thickness on cylinder wallHoles in ring and piston allow excess oil to drain back to crankcaseToo much oil film and the engine will use excessive oil and too little oil causes heat and insufficient lubrication

Oil scraper ringsDirects the oil away from or towards the oil control rings depending upon the requirements of the engine

Piston ring end gapThe gap at the end of the rings allows for expansion and contraction and unevenness in the cylinder wallButt, step and angle types Always stagger the end gaps during ring installation to prevent losing compression

Piston Pins (wrist pins)Connects the piston to the end of the connecting rodConstructed of hardened steelThe pin is retained in the piston with clips or plugs to prevent cylinder wall scoringTypical Lycoming and Continental pins are free-floating, meaning the pin is not secured to the piston or the rod.

Connecting Rod Assembly

The link between the crankshaft and the pistonNormally steel but some low powered engines use aluminum to save weightCross section is an H or ITypes include : Plain RodFork and blade rodMaster and articulated

Plain Type Rods

Used on inline and opposed enginesSmall bushing at piston pin end is pressed in place and reamed to final dimensionsLarge end of rod includes a cap, bolts, nuts, and plain bearing insertsRods are numbered as to cylinder and for cap-to-rod alignment

Fork and Blade Connecting Rod

Used on V type enginesOne rod inside another allows cylinders to be aligned and to share a common location on the crankshaft

Master and Articulating Rod

Used on radial enginesUses knuckle pins to retain articulated rods to masterMaster RodArticulating Rod

Master/Articulating Rod in Action

CrankshaftChanges reciprocating motion of pistons into rotating motion to drive propellerConstructed of chrome-nickel-molybdenum-steelMay be one piece or as many as three separate piecesThe propeller mounts to the front of the crankshaft using a spline, taper, or flangeThe crankshaft rotates within the crankcase and is supported by main bearing journalsCrankshaft throws or crankpins are off center and account for the reciprocating motion of the pistons

Crankshaft Main Bearing Journal, Pin, Arm

Crankshaft Ends For Mounting Propellers

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 floatCounterweights and dampers are used in piston engines because the power pulses and movement of the pistons create large amounts of vibrationVibration shortens airframe and engine life and can lead to premature component failureThe engine is also mounted in rubber bushings to absorb vibration

2 Piece Crankshaft With Counterweights (Single Throw, Single Cylinder)

Valves and the Valve SystemValves control the flow of gases inside the enginePoppet valves are the most common and get their name from the popping open and closed during operationIntake valves are chrome steel and are cooled by the incoming air and fuel mixtureExhaust 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 corrosionValve faces are ground to 30 degrees for intake (airflow) and 45 degrees (cooling) for exhaust

1290 degrees F (typical)

Valve SpringsInner and outer springs are used to prevent bounce, provide redundancy, and increase valve closing pressureHeld in place by retainer washers on the top and bottom of the springSplit key or keeper holds the retainers and springs in place on the valve stem

Valve Lifter or Tappet

May be solid, roller, or hydraulicThe lifter follows the cam lobes and pushes on the pushrodSolid and roller lifters require adjustable rocker armsHydraulic type lifters fill with oil and lengthen to compensate for any clearances in the valve system

CamshaftTurns at 1/2 the speed of the crankshaftMust be mechanically coupled to the crankshaft for timing purposes (gears, belts, chains)The camshaft consists of bearing journals and lobes spaced along the shaftEach lobe is positioned to open and close a valve at a specific timeLobe

Pushrodtransmits push of lifter up to rocker armHollow to allow oil to flow to the top of the cylinder for valve part lubricationLength can be varied to adjust valve clearanceValve 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 compressionvalve clearance increases as the engine operates due to cylinder expansion (solid lifters)Hydraulic lifters have a 0 clearance in operation

Valve clearance adjustmentValve clearance measurement

Rocker ArmAdjustable in solid lifter engines and fixed in engines with hydraulic liftersOne end rests on the valve stem and the other on the pushrodRocking motion opens and closes the valvesRoller rocker arms incorporate a roller that reduces friction and are used in some radials and experimental engines

BearingsMust be able to withstand forces inside an engine with minimal friction and heat build-up. Must accept radial and thrust loads

Plain BearingsA steel insert with babbitt (lead alloy) bonded to the bearing surfacePlain bearings are keyed to keep them in place A lip or flange allows the plain bearing to accept thrust loadsCommonly used as crankshaft and rod bearings in opposed engines

Roller Bearings (antifriction)Hard steel rollers captured between an inner and outer race and held in alignment by a cageMay be tapered to absorb radial and thrust loads or straight to absorb radial loads only

Parts of a Ball BearingOUTER RACEINNER RACECAGEBALL

Ball Bearings (antifriction)Used for both radial and thrust loadsDeep grooves in races allow thrust loads

Bearing cleaning and safety

Wash old grease and debris with solventBlow dry with shop air but do not spin the bearing with the air blastReapply grease or oil immediately to prevent corrosionProtect skin and eyes from solvent contact

Propeller Reduction Gearing

Purpose is to reduce propeller rpm to its optimal speed and to increase engine rpm to its optimal speedPropeller always turns slower than the engine

Gear Ratios:Expressed as 2:1, .64:1, 300:1At what speed will the propeller be turning if the engine rpm is 2000 and the gear ratio is 2:1?1000 rpm

Which reduction ratio will provide the fastest propeller speed 10:1 or 4:1?4:1 (it is the closest to 1:1)

Spur GearsSimple drive and driven gear systemNumber of teeth on gear and gear diameters determine reduction ratioLarge gear would be mounted to propeller as it turns the slowest

Planetary Gears

Ring gear, Planet gear, Sun gearLarge gear reductions possibleCompact and versatileCommon in large radials and turbine engines