1. Modern Automotive Technology PowerPoint for by Russell Krick
Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois

2. Chapter 14
Lesson 1
Engine Bottom End
Construction

3. Contents
(2 Topics)
Cylinder block construction
Piston construction

4. Includes the block, crankshaft, connecting rods, and piston assemblies
Engine Bottom End
Includes the block, crankshaft, connecting rods, and piston assemblies

5. Cylinder Block Construction
Engine cylinder blocks are normally made of cast iron or aluminum
Cast iron is very heavy and strong
Aluminum is relatively light and dissipates heat well

6. Cylinder Block
Cylinders may be integral parts of the block or formed by pressed-in liners

7. Cylinder Sleeves
Metal, pipe-shaped inserts that fit into the cylinder block
act as cylinder walls
Cast iron sleeves are commonly used in aluminum cylinder blocks
Sleeves can also be installed to repair badly damaged cylinder walls in cast iron blocks

8. Cylinder Sleeves There two basic types of sleeves: dry sleeves
wet sleeves

9. Dry Sleeve Presses into a cylinder that has been bored oversize
Made from relatively thin material
Not exposed to engine coolant
The outer surface touches the walls of the cylinder block

10. Wet Sleeve Exposed to the engine coolant
Thicker construction than a dry sleeve
Designed to withstand combustion pressure and heat without the added support of the cylinder block

11. Sleeve Installations
Dry sleeve Wet sleeve

12. Aluminum cylinder block with pressed-in, cast iron wet sleeves
Sleeve Installations
Aluminum cylinder block with pressed-in, cast iron wet sleeves

13. Line Boring
Machining operation that cuts a series of holes through the block for the crankshaft or camshaft bearings
Holes must be in perfect alignment for the crankshaft or camshaft to turn freely

14. Two- and Four-Bolt Mains
Two-bolt main block
uses two cap screws to secure each main bearing cap to the block
Four-bolt main block
uses four cap screws to hold each main cap
used on high-performance engines
with extra bolts, the block can withstand more crankshaft downward pressure

15. Crossbolted Block
Has extra cap screws going in through the sides of the block and main caps for added strength
Often used on high-performance engines

16. Block Girdle Also called a main bearing bedplate
Large one-piece cap that fits over the entire bottom of the block
All the main caps are formed as one piece to increase strength and block stiffness

17. Piston Construction
Pistons are normally cast or forged from an aluminum alloy
Cast pistons
relatively soft, used in slow-speed, low-performance engines
Forged pistons
used in fuel-injected, turbocharged, and diesel engines

18. Piston Dimensions

19. Cam-Ground Piston Slightly out-of-round when viewed from the top
Machined a few thousandths of an inch larger in diameter perpendicular to the piston pin centerline
compensates for different rates of expansion due to differences in metal wall thickness

20. Cam-Ground Piston

21. Cam-Grind Theory
As the piston is heated, the thicker area around the pin boss causes the piston to expand more parallel to the piston pin
The piston becomes round when hot
A cam-ground piston maintains the correct piston-to-cylinder clearance when cold and at operating temperature

22. Piston Taper Used to maintain the correct piston-to-cylinder clearance
The top of the piston is machined slightly smaller than the bottom
Since the piston head gets hotter than the skirt, it expands more
The piston is almost equal in size at the top and bottom at operating temperature

23. Piston Taper

24. Piston Shape Refers to the contour of the piston head
Piston head is shaped to match and work with the shape of the combustion chamber
Piston may have a flat top or a domed head

25. Slipper Skirt
Produced when the portions of the piston skirt below the piston pin ends are removed
Provides clearance between the piston and the crankshaft counterweights
Piston can slide farther down in the cylinder without hitting the crankshaft

26. Slipper Skirt Piston