Powplant Quiz 2

CRANKSHAFT

CRANKSHAFT

Backbone of a reciprocating engine and Transforms the reciprocating motion of the pistons and connecting rods into rotary motion to turn a propeller.

Material: Forged from a strong alloy such as chromium-nickel molybdenum steel.

MAIN BEARING JOURNAL

Represents the centerline of a crankshaft, and supports it in the main bearings. At least two main journals to support the crankshaft, absorb loads, and transmit stress.

CRANKPIN

Serves as attachment points for the connecting rods, offset from the main bearing journal. This offset design means that any force applied to a crankpin in a direction other than parallel to the crankshaft center line causes the crankshaft to rotate.

CRANK CHEEK/CRANK ARMS

Connects crankpin to the crankshaft, may extend beyond the journal to form counterweights.

CRANKSHAFT BALANCE: Static Balance

Entire crankshaft assembly balanced around its axis of rotation.

CRANKSHAFT BALANCE: Dynamic Balance

Balancing of centrifugal forces and power impulse forces using dynamic dampers.

True

Once a crankshaft is statically balanced it must be dynamically balanced

True

Number of crankpins must correspond with cylinder arrangement.

DYNAMIC DAMPER

absorbs crankshaft vibrations by oscillating opposite to vibration pulses each time a cylinder fires.

Single-Throw/360 degree crankshaft

Used in single-row radial engines. Consists of one crankpin, two main journals; simplest.

CONNECTING RODS

Link which transmits force from piston to crankshaft. Materials: Durable steel alloy or aluminum

Types of Connecting Rod Assemblies:

'Plain-Type

Used in opposed and inline engines.

Types of Connecting Rod Assemblies:

Master-and-Articulated-Rod Type

Common in radial engines.

Articulated Rods

Connect other pistons to master rod; Hinged to the master rod by knuckle pins.

Master Rod

Connects one piston per row directly to crankshaft. Only connecting link between all pistons and the crankpin.

Knuckle Pins

prevent rotation in flange holes and travels in a true circle as the crankshaft rotates.

Fork-and-Blade Type

Used in V-type engines and consists of a fork connecting rod and a blade connecting rod.

Forked Rod

Split at crankpin end to fit blade rod between prongs.

Blade Rod

Fits between forked rod prongs.

PISTONS

Cylindrical plunger that moves up and down within a cylinder.

Material: Machined from aluminum alloy forgings.

Ring Grooves

Cut into the outside surface to hold piston rings (up to six grooves)

Ring Land

Portion between the ring grooves.

Piston Head

Top surface exposed to the heat of combustion.

Piston Pin Boss

Enlarged area inside providing bearing area for the piston pin.

Piston Skirt

Extended base to help align the piston in the cylinder.

Cooling Fins

Cast into the underside for heat transfer (on some pistons).

PISTON HEAD

Flat, recessed, cupped, and domed.

CAM GROUND PISTON

• Slightly oval

• Compensates for differential expansion

PISTON RINGS

• Prevent gas leakage

• Reduce oil seepage

• Transfer heat from the piston to the cylinder walls.

PISTON RING GAP

• point where a piston ring is split.

• Butt joint, angle joint, step joint

True

Piston Ring Gaps must be staggered or offset to prevent alignment, avoiding blow-by, loss of power, and increased oil consumption. With three piston rings, gaps are staggered 120 degrees apart.

COMPRESSION RINGS

Prevent gas from escaping past the piston.

OIL RINGS

Control oil application to cylinder walls and prevent oil from entering the combustion chamber.

OIL CONTROL RINGS

Regulate oil film thickness on the cylinder wall.

OIL SCRAPER RINGS/OIL WIPER RING

Regulate oil passage between the piston skirt and cylinder wall.

PISTON PINS

Joins the piston to the connecting rod.

Material: Nickel-steel alloy forging, case-hardened.

Other Name: Wrist pins

Stationary Piston Pins

Held tightly by a setscrew, preventing movement.

Semi-Floating Piston Pins

Stationary in the connecting rod, retained by a set clamp.

Full-Floating Piston Pins

Free to rotate in both the connecting rod and piston, used in most modern aircraft engines.

CYLINDER

Provides a combustion chamber for burning and expansion of gases to produce power; houses the piston and connecting rod assembly, valves, and spark plugs.

Material: Must have good heat-conducting properties for efficient cooling.

True

Individual cylinders are cast as components separate from the crankcase, heads permanently attached during manufacturing.

CYLINDER BARREL

Machined from a forged blank, with a skirt projecting into the crankcase and a mounting flange for attachment to the crankcase.

NITRIDING

Case hardening method changing surface strength by infusing metal with a hardening agent.

CHROME PLATING

Hardening by applying a thin chromium coating through electroplating.

CYLINDER BORE

Inside is machined smooth to a uniform dimension, then, honed to final dimension.

CHOKE BORE CYLINDER

Compensates for uneven expansion due to higher temperatures and mass near the cylinder head.

Choke Amount: Usually between .003 and .005 inches.

CYLINDER HEAD

Acts as a lid on the cylinder barrel for an enclosed combustion chamber.

CYLINDER NUMBERING

Propeller shaft end is the front, accessory end is the rear of an engine.

True

Crankshaft Rotation: Referenced from the rear, specified as clockwise or counterclockwise.

Teledyne Continental Cylinder Numbering

Numbers start with the most rearward cylinder.

Textron Lycoming Cylinder Numbering

Numbers start with the most forward cylinder.

True

Commonality of Teledyne and Textron: Odd-numbered cylinders on the right, even-numbered on the left.

CYLINDER NUMBERING (RADIAL)

• Single-Row: Numbered consecutively from the top, clockwise from the rear.

• Double-Row: Odd-numbered cylinders in the rear row, even-numbered in the front row.

VALVES

Regulate gas flow into and out of a cylinder, opening and closing at predetermined times.

True

Each cylinder has at least one intake and one exhaust valve. (2 on some high-powered)

Intake Valves

controls the amount of fuel/air mixture that enters a cylinder through the intake port.

Material: Chrome, nickel, or tungsten steel (lower temperatures).

Exhaust Valves

allows the exhaust gases to exit the cylinder through the exhaust port.

Material: Inconel, silicon-chromium, or cobalt-chromium alloys (higher temperatures).

Poppet Valve

Most common Valve type, named for the popping action.

Poppet Valves Head Shapes:

• Flat-headed - typically used only as an intake valve

• semi-tulip - has a slightly concave area on its head

• tulip - has a deep, wide indented area on its head.

• mushroom valve - have convex heads. (not common)

VALVE FACE

• Creates a seal at the intake and exhaust ports.

• Typically ground to between 30 and 60 degrees.

• Material: Stellite (cobalt and chromium alloy).

VALVE STEM

Keeps valve head aligned during back-and-forth movement.

True

Some exhaust stems are hollowed and partially filled with metallic sodium for heat dissipation.

True

Some valves are filled with metallic sodium to lower operating temperatures. The sodium melts during operation, transferring heat to the valve stem, which is then conducted away by the cylinder head.

SPLIT KEY

Acts as a lock ring to keep valve spring retaining washers in place and hold the valve in the cylinder head.

True

A valve's face must sit firmly against the cylinder head.

VALVE SEAT

• circular ring that provides a uniform sealing surface for the valve face.

• Material: bronze or steel and machined to an oversize fit.

VALVE GUIDE

• cylindrical sleeve that supports the valve stem, aligning the valve face with the seat.

• Material: steel, tin-bronze, or aluminum-bronze, and installed in the cylinder head using a shrink fit.

VALVE SPRING

helical -coiled springs that holds the valve face firmly against the valve seat, preventing valve float or valve surge.

Valve float

occurs when the frequency of a valve spring begins to vibrate at its resonant frequency, the spring loses its ability to hold the valve closed.

Crankshaft components

• Main bearing journal

• Crankpin

• Crank cheek

• Counterweights and dampers

Piston components

• Ring Grooves

• Ring Land

• Piston Head

• Piston Pin Boss

• Piston Skirt

• Cooling Fins

Cylinder components

• Cylinder head

• barrel

• mounting flange

• skirt

• cooling fins

• valve assembly.

Valve seating components

• Valve seats

• valve guides

• valve springs

• valve spring retainers