Piston engine construction

Piston engine construction, parts and materials.

1. Reciprocating engine components

2. 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 ) C rankcase

3. 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) C rankcase

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

5. C rankshaft

6. 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 C rankshaft

7. C rankshaft

8. 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 C rankshaft

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

10. Camshaft

11. 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 Camshaft

12. Sump

13. 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.  Sump

14. Accessory gearbox

15. 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.   Accessory gearbox

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

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

21. Piston

22. 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 Piston

23. Ring

24. 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. Ring

25. 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. Ring

26. Piston Pin

27. 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 Piston Pin

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

29. Connecting rod

30. 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 Connecting Rod