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

2. Chapter 14
Lesson 2
Engine Bottom End
Construction

3. Contents Piston ring construction Piston pin construction
(3 Topics)
Piston ring construction
Piston pin construction
Connecting rod construction

4. Piston Ring Construction Automotive pistons normally use three rings:
two compression rings
one oil ring

5. Compression Rings Prevent pressure leakage into the crankcase
Wipe some of the oil from the cylinder walls
Usually made of cast iron
An outer layer of chrome or other metal may be used to increase wear resistance

6. Compression Rings

7. Oil Rings Keep crankcase oil out of the combustion chambers
Available in two basic designs:
rail-spacer type (three piece)
one-piece type

8. Oil Rings Rail-spacer ring (most common)
One-piece ring made from cast iron

9. Piston Ring Dimensions

10. Piston Ring Gap
Distance between the ends of the ring when installed in the cylinder
Allows the ring to be installed on the piston and to “spring” outward in its cylinder
Allows the ring to conform to any variation in the cylinder diameter due to wear

11. Most piston rings use a butt joint
Piston Ring Gap
Most piston rings use a butt joint

12. Piston Ring Coatings Soft ring coatings Hard ring coatings
porous metal, such as iron
help the ring wear in quickly
the outer surface will wear away rapidly so the ring conforms to the shape of the cylinder
Hard ring coatings
chrome or moly
increase ring life and reduce friction
used in new or freshly machined cylinders

13. Piston Pin Construction
Piston pins are normally made of case-hardened steel, which increases the wear resistance
A hollow piston pin is machined and polished to a very precise finish

14. Piston Pins Piston pins are held in the piston by one of two means:
snap rings (full-floating piston pin)
press-fit

15. Full-Floating Piston Pin
Secured by snap rings
Free to rotate in both the rod and piston

16. Press-Fit Piston Pin
Forced tightly into the connecting rod’s small end and free to rotate in the piston pin hole

17. Piston Pin Offset
Locates the piston pin hole slightly to one side of the piston centerline
Helps quiet the piston during use
The piston pin hole is moved toward the piston’s major thrust surface
the thrust surface is the surface of the piston that is pushed tightly against the cylinder wall during the power stroke

18. The piston notch indicates the front of the piston
Piston Assembly
The piston notch indicates the front of the piston

19. This piston has a full-floating piston pin
Piston Assembly
This piston has a full-floating piston pin

20. Connecting Rod Construction Most connecting rods are made of steel
Connecting rods normally have an I-beam shape for a high strength-to-weight ratio

21. Connecting Rod Features
Oil spurt holes
provide added lubrication for the piston pin, cylinder walls, and other parts
Drilled rod
allows oil to enter the clearance between the pin and bushing

22. Connecting Rod Features
A. Oil spurt holes
B. Drilled rod

23. Connecting Rod Numbers
Ensure that each connecting rod is in the proper location and that the rod cap is installed on the corresponding rod body correctly

24. Broken-Surface Rod The rod is scribed and broken off when manufactured
Produces a rough, irregular mating surface between the rod and cap
Done to help lock the rod and cap into alignment

25. Powdered Metal Forging
Forms the rough shape of the part out of metal powder before final shaping in a powerful forge
Helps control the shape and weight while reducing machining

26. Machined Block Forging
Involves initial turning in a lathe to bring the blank of metal to size before forming it in a drop forge
Helps eliminate flashing
flashing is a small blip of rough metal produced when the two halves of the forge come together to “smash” the metal into shape