The crankcase supports and encloses the crankshaft and provides an oil reservoir. It holds the engine parts in alignment and supports the cylinders and crankshaft. The crankshaft rotates within the crankcase and is supported by main bearing journals, with throws that account for the reciprocating motion of the pistons. The camshaft opens and closes the valves using lobes timed to the crankshaft.

1. Reciprocating engine components

2. Crankcase
• The crankcase is that part of the engine block below the cylinders. It supports and
encloses the crankshaft and provides a reservoir for the lubricating oil.
• 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)

3. Crankcase
• 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)

4. Crankcase
• Opposed crankcase
• Sections are not as distinct as in the radial and the crankcase splits from front
to rear instead of in radial sections

5. Crankshaft

6. Crankshaft
• Constructed of chrome-nickel-molybdenum-steel
• May be one piece or as many as three separate pieces
• The crankshaft rotates within the crankcase and is supported by main bearing journals
• Crankshaft throws or crankpins are off center and account for the reciprocating motion of
the pistons

7. Crankshaft

8. Crankshaft
• Counterweights are used to reduce vibration but they are rigid
• Counterweights 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

9. Crankshaft
• 2 Piece Crankshaft With Counterweights (Single
Throw, Single Cylinder)

10. Camshaft

11. Camshaft
• Used to open the valves for intake and exhaust
• 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

12. Sump

13. Sump
• reservoir for the lubricating oil.
• A wet sump is a lubricating oil management design for piston engines which uses
the crankcase as a built-in reservoir for oil.
• Piston engines are lubricated by oil which is pumped into various bearings, and
thereafter allowed to drain to the base of the engine under gravity.
• A wet sump offers the advantage of a simple design, using a single pump and no
external reservoir.

14. Accessory gearbox

15. Accessory gearbox
• The accessory drive gearbox is most often attached directly to the outside cases of the
engine at or near the bottom.
• The accessory gearbox is driven the crankshaft of the engine.
• The gearbox has attachment pads on it for accessories that need to be mechanically driven.

16. Cylinder barrel

17. 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

18. Cylinder head
• Valve
• Spark plug

19. Cylinder head
• Cylinder heads
• Constructed of cast aluminum alloy
• Provides combustion chamber, and
mounting areas for spark plugs and
valve parts

20. Cylinder head
• The cylinder head is designed to transfer heat by conduction to the
fins and then from the fins to the air by convection

21. Piston

22. Piston
• 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

23. Ring

24. Ring
• 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 ring is to prevent gases from leaking by the piston during the
compression and power strokes.
• The oil ring, usually located just above the piston pin,it is an oil-regulating ring.
This ring scrapes the excess oil from the cylinder walls and returns some of it,
through slots, to the piston ring grooves.

25. Ring
• The gap at the end of the rings allows for expansion and contraction
and unevenness in the cylinder wall .
• Always place the end gaps during ring installation away from each
other to prevent losing compression.

26. Piston Pin

27. Piston Pin
• The piston is attached to the connecting rod by the piston pin (wrist pin).
• Piston pins are made of alloy steel with a precision finish
• They are lubricated by splash from the crankcase or by
pressure passages bored in the connecting rods
• The pin is retained in the piston with clips or plugs to prevent cylinder wall scoring

28. Piston Pin
• Three methods are commonly used for fastening a piston pin to the piston and the
connecting rod

29. Connecting rod

30. Connecting Rod
• Connecting Rod Assembly
• The link between the crankshaft and the piston
• Normally steel but some low powered engines use aluminum to save weight
• Types include : Plain Rod
Fork and blade rod
Master and articulated