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© 2011 Pearson Education, Inc.All Rights Reserved
Automotive Technology, Fourth EditionJames Halderman
PISTONS, RINGS, AND CONNECTING RODS
33
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
ObjectivesObjectives
• The student should be able to:– Prepare for Engine Repair (A1) ASE
certification test content area “C” (Engine Block Diagnosis and Repair).
– Describe the purpose and function of pistons, rings, and connecting rods.
– Explain how pistons and rods are constructed and what to look for during an inspection.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
ObjectivesObjectives
• The student should be able to:– Discuss connecting rod reconditioning
procedures.– Explain how piston rings operate and how
to install them on a piston.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PISTONSPISTONS
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PistonsPistons
• Purpose and Function– Three purposes
• Transfers force• Seals the combustion chamber• Conducts heat
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PistonsPistons
• Parts Involved– Piston– Wrist pin– Crank throw/crankpin/connecting rod
bearing journal– Piston rings
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-1 The piston seals the bottom of the combustion chamber and is attached to a connecting rod.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PistonsPistons
• Piston Operation– Starts, accelerates, and stops twice in each
crankshaft revolution– Piston starts at the top of the cylinder and
ends at the top of the stroke
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PistonsPistons
• Piston Operation– Piston head exposed to the hot combustion
gases – Skirt contacts the relatively cool cylinder
wall• Results in a temperature difference of about
275°F (147°C) between the top and bottom of the piston
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PistonsPistons
• Piston Operation– NOTE: A typical piston in an engine
operating at 4000 RPM accelerates from 0 to 60 mph (97 km/h) in about 0.004 second (4 ms) as it travels about halfway down the cylinder.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PISTON PISTON CONSTRUCTIONCONSTRUCTION
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Construction Piston Construction
• Piston Ring Grooves– Located between the piston head and skirt– Factors that determine minimum piston
height:• Width of grooves
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Construction Piston Construction
• Piston Ring Grooves– Factors that determine minimum piston
height:• Width of lands between ring grooves• Number of rings
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Construction Piston Construction
• Piston Ring Grooves– Outside diameter lands is about 0.02 to
0.04 in. (0.5 to 1 mm) smaller than the skirt diameter
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-2 All pistons share the same parts in common.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-3 A piston diameter is measured across the thrust surfaces.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Cast Pistons– Usually made using gravity die casting– Molten aluminum alloy and about 10%
silicon are poured into a mold
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Cast Pistons– Silicon increases the strength and helps
control the expansion of the piston when it gets hot
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Cast Pistons– Metals used in the aluminum alloy include
copper, nickel, manganese, and magnesium
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-4 A cast piston showing the sprues which were used to fill the mold with molten aluminum alloy.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Hypereutectic Pistons– Eutectic pistons contain about 9% to 12%
silicon – Hypereutectic pistons are stronger due to a
16% silicon content
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Hypereutectic Pistons– Advantages:
• Strength• 25% weight reduction • Lower expansion rate
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Hypereutectic Pistons– Disadvantages:
• Higher cost• More difficult to cast and machine
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Forged Pistons– Dense grain structure– Very strong– Often used in turbocharged or
supercharged engines
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Forged Pistons– Less porous than cast pistons– Conduct heat more quickly than cast
pistons– Run about 20% cooler than cast pistons
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-5 The top of the piston temperature can be 100°F (38°C) lower on a forged piston compared to a cast piston.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Head Designs– Shape is vital to the combustion process
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Head Designs– Flat-top pistons
• Close to the cylinder head • Recesses are cut in the piston top for valve
clearance– Commonly called: eyebrows, valve reliefs,
valve pockets
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Head Designs– Pistons in high-powered engines may have
raised domes (pop-ups) on the heads
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Head Designs– Pistons in other engines may be provided
with a depression (dish)– Varying dish depths provide different
compression ratios
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Head Designs– NOTE: Newer engines do not use valve
reliefs because this requires that the thickness of the top of the piston be increased to provide the necessary strength. The thicker the top of the piston, the farther down from the top the top piston ring sits.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Head Designs– NOTE: To reduce unburned hydrocarbon
(HC) exhaust emissions, engineers attempt to place the top piston ring as close to the top of the piston as possible to prevent the unburned fuel from being trapped (and not burned) between the top of the piston and the top of the top piston ring.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-6 Valve reliefs are used to provide valve clearance.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Slipper Skirt Pistons– Shorter on the two sides that are not thrust
surfaces– Advantages include:
• Lighter weight
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Slipper Skirt Pistons– Advantages include:
• Allows for shorter overall engine height
– Most engines today use a slipper skirt piston
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Cam Ground Pistons– Provides method of expansion control – Piston thrust surfaces closely fit the
cylinder– Piston pin boss diameter is fitted loosely
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Cam Ground Pistons– Expands along the piston when heated– Nearly round at its normal operating
temperatures
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-7 Piston cam shape. The largest diameter is across the thrust surfaces and perpendicular to the piston pin (labeled A).
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Finish– Varies with manufacturer– All finishes reduce scuffing (condition
where the metal of the piston actually contacts the cylinder wall)
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Finish– Reduce scuffing by coating piston skirts
with tin 0.0005 in. (0.0125 mm) thick or a moly graphite coating
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-8 A moly graphite coating on this piston from a General Motors 3800 V-6 engine helps to prevent piston scuffing.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Head Size– Smaller in diameter than the rest of piston– Horizontal separation slots act as heat
dams
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Head Size– Slots reduce heat transfer from the piston
head to the lower skirt• Keeps the skirt temperature lower to reduce
skirt expansion• Can be used for oil drainback and expansion
control
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-9 The head of the piston is smaller in diameter than the skirt of the piston to allow it to expand when the engine is running.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Strut Inserts– Add strength to the piston in the piston pin
area– Help control thermal expansion
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston ConstructionPiston Construction
• Piston Strut Inserts– Good piston-to-cylinder wall clearance at
normal temperatures– Cold operating clearance as small as
0.0005 in. (0.0127 mm)• Will prevent cold piston slap and noise
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-10 Steel struts cast inside the piston help control expansion and add strength to the piston pin area.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PISTON PINSPISTON PINS
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston PinsPiston Pins
• Terminology– Attaches the piston to the connecting rod– Also known as wrist pins or gudgeon pins
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston PinsPiston Pins
• Terminology– Transfers the force produced by
combustion chamber pressures and piston inertia to the connecting rod
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston PinsPiston Pins
• Terminology– Made from high-quality steel in the shape
of a tube – Interior hole is sometimes tapered
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-11 Most piston pins are hollow to reduce weight and have a straight bore. Some pins have a tapered bore to reinforce the pin.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Pins Piston Pins
• Piston Pin Offset– Some piston pin holes are not centered in
the piston– Located toward the major thrust surface,
approximately 0.062 in. (1.57 mm) from the piston centerline
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Pins Piston Pins
• Piston Pin Offset– Designed to reduce piston slap and the
noise• Minor thrust• Major thrust
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Pins Piston Pins
• Piston Pin Offset– NOTE: Not all piston pins are offset. In fact,
many engines operate without the offset to help reduce friction and improve power and fuel economy.
?
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-12 Piston pin offset toward the major thrust surface.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-13 Engine rotation and rod angle during the power stroke cause the piston to press harder against one side of the cylinder, called the major thrust surface.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston PinsPiston Pins
• Piston Pin Fit– Size is held to tens of thousandths of an
inch– Loose pins will make a sound while engine
is running (double knock)
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston PinsPiston Pins
• Piston Pin Fit– Tight pins will restrict piston expansion
along the pin diameter and lead to piston scuffing
– Normal clearances range from 0.0005 to 0.0007 in. (0.0126 to 0.018 mm)
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PISTON PIN RETAINING PISTON PIN RETAINING METHODSMETHODS
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Pin Retaining Methods Piston Pin Retaining Methods
• Full Floating– Free to “float” in the connecting rod and
the piston– Retaining device keeps piston from
scraping against the cylinder wall
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Pin Retaining Methods Piston Pin Retaining Methods
• Full Floating– Most often used in high-performance
modified engines– Some type of lock ring used to retain the
piston pin
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Pin Retaining Methods Piston Pin Retaining Methods
• Full Floating– Two common types of lock rings:
• Internal snap ring• Spiral lock ring
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-14 Circlips hold full-floating piston pins in place.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Pin Retaining MethodsPiston Pin Retaining Methods
• Interference Fit– Connecting rod hole slightly smaller than
the piston pin– Pin is installed by heating the rod or by
pressing it into the rod
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Pin Retaining MethodsPiston Pin Retaining Methods
• Interference Fit– Be careful to have the correct hole sizes
and center the pin – Least expensive method to use
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-15 A typical interference fit piston pin.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PISTON RINGSPISTON RINGS
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Purpose and Function– Form a sliding combustion chamber seal to
prevent the high-pressure combustion gases from leaking past the piston
– Keep engine oil from entering the combustion chamber
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Purpose and Function– Transfer some of the piston heat to the
cylinder wall, where it is removed from the engine through the cooling system
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-16 The rings conduct heat from the piston to the cylinder wall.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Classifications– Classified in two types:
• Two compression rings• One oil control ring
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Classifications– NOTE: Some engines, such as Honda high-
fuel economy engines, use pistons with only two rings: one compression ring and one oil control ring.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Compression Rings– Forms seal between the moving piston and
the cylinder wall to get maximum power from the combustion pressure
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Compression Rings– Must keep friction at a minimum– Space in the ring groove above the ring is
called side clearance – Space behind the ring is called the back
clearance
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-17 Combustion chamber pressure forces the ring against the cylinder wall and the bottom of the ring groove to effectively seal the cylinder.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-18 The side and back clearances must be correct for the compression rings to seal properly.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Oil Control Rings– Scraping action allows oil to return through
the expander and openings in the piston– Spacer expander lies between the top and
bottom rails
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Oil Control Rings– Spacer expander keeps the rails separated
and pushes them out against the cylinder wall
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-19 This typical three-piece oil control ring uses a hump-type stainless steel spacer-expander. The expander separates the two steel rails and presses them against the cylinder wall.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Ring Gap– Allow some leakage past the top
compression ring• Leakage provides pressure on the second
ring to create seal
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Ring Gap– Amount of gap is critical
• A gap that is too great will allow excessive blowby (leakage of combustion gases past the rings)
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Ring Gap– Amount of gap is critical
• A gap that is too little will allow the piston ring ends to touch together when the engine is hot, causing excessive wear and possible engine failure
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Ring Gap– Gaps reduce losses of high-pressure
combustion gases
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-20 Typical piston ring gaps.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Piston Ring Shapes– Taper face ring– Positive twist ring– Reverse twist ring
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston RingsPiston Rings
• Piston Ring Shapes– Scraper ring– Barrel face ring
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-21 The taper face ring provides oil control by scraping the cylinder wall. This style of ring must be installed right side up or the ring will not seal and oil will be drawn into the combustion chamber.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-22 Torsional twist rings provide better compression sealing and oil control than regular taper rings.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-23 Scraper-type rings provide improved oil control.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-24 The upper barrel face ring has a line showing contact with the cylinder wall. The second taper face ring shows contact along the lower edge of the ring.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PISTON RING PISTON RING CONSTRUCTIONCONSTRUCTION
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Piston Ring Materials– Plain cast iron– Pearlitic cast iron– Nodular cast iron
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Piston Ring Materials– Steel– Ductile iron
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Chromium Piston Rings– Greatly increases piston ring life– Slightly chamfered at the outer corners– Rings are prelapped or honed before
packaging
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-25 The chrome facing on this compression ring is about 0.004 in. (0.10 mm) thick.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Molybdenum Piston Rings– Introduced in the early 1960s– Plasma method is a spray method used to
deposit molybdenum on cast iron to produce a long-wearing and low-friction piston ring
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Molybdenum Piston Rings– Most have a 0.004 to 0.008 in. (0.1 to 0.2
mm) groove filled with molybdenum cut into its face
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Molybdenum Piston Rings– Will survive under high-temperature and
scuffing conditions better than chromium face rings
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-26 The moly facing on this compression ring is about 0.005 in. (0.13 mm) thick.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Moly-Chrome-Carbide Rings– Used in some original equipment (OE) and
replacement applications
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Moly-Chrome-Carbide Rings– Coating properties hardness of chrome and
carbide combined with heat resistance of molybdenum
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ConstructionPiston Ring Construction
• Ceramic-Coated Rings– Ceramic coating applied through a process
called physical vapor deposition (PVD)– Used when additional heat resistance is
needed
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
CONNECTING RODSCONNECTING RODS
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Purpose and Function– Transfers the force and reciprocating
motion of the piston to the crankshaft
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Purpose and Function– Small end reciprocates with the piston– Large end rotates with the crankpin
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Purpose and Function– Connecting rods are manufactured by
casting, forging, and powdered (sintered) metal processes
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-27 The connecting rod is the most highly stressed part of any engine because combustion pressure tries to compress it and piston inertia tries to pull it apart.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-28 The I-beam shape (top rod) is the most common, but the H-beam shape is common in high-performance and racing engine applications.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Connecting Rod Design– Big end must be a perfect circle– Once a rod and cap are initially machined,
they must remain a “matched set”
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Connecting Rod Design– Assembly bolt holes are closely reamed in
both the cap and connecting rod to ensure alignment
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Connecting Rod Design– Bolts have piloting surfaces that closely fit
the reamed holes– Made with balancing bosses (pads) so
weight can be adjusted to specifications
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Connecting Rod Design– Some have a spit hole that bleeds some of
the oil from the connecting rod journal
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-29 Rod bolts are quickly removed using a press.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-30 Some rods have balancing pads on each end of the connecting rod.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-31 Some connecting rods have spit holes to help lubricate the cylinder wall or piston pin.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-32 Some engines, such as this Ford diesel, are equipped with oil squirters that spray or stream oil toward the underneath side of the piston head to cool the piston.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Cast Connecting Rods– Can be identified by their narrow parting
line
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Forged Connecting Rods– Generally used in heavy-duty and high-
performance engines– Lighter weight and stronger but more
expensive
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Forged Connecting Rods– Can be identified by their wide parting line– Many high-performance rods use a bronze
bushing in the small end
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-33 A cast connecting rod is found on many stock engines and can be identified by the thin parting line.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-34 This high-performance connecting rod uses a bronze bushing in the small end of the rod and oil hole to allow oil to reach the full-floating piston pin.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Powdered Metal Connecting Rods– Used by most new production engines– Advantages over convention cast (forged)
rods including precise weight control
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Powdered Metal Connecting Rods– Created with measured amount of material
so rod and engine are balanced without extra weighting and machining operations
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Powdered Metal Connecting Rods– Start as powdered metal (iron, copper,
carbon, other alloying agents)– Powder placed in a die and compacted
(forged)
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Powdered Metal Connecting Rods– Part is heated, without melting, to about
2,000°F. – Ingredients are transformed into
metallurgical bonds
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting RodsConnecting Rods
• Powdered Metal Connecting Rods– Machining includes boring and drilling – Big end is fractured to help ensure a
perfect match when assembled
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-35 Powdered metal connecting rods feature a fractured parting line at the big end of the rod.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
CONNECTING ROD CONNECTING ROD SERVICESERVICE
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting Rod ServiceConnecting Rod Service
• Removing Pistons From Rods– Removed using a special fixture
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting Rod ServiceConnecting Rod Service
• Inspection– Check rod for a twist before reconditioning – Hole at the small end and the hole at the
big end should be parallel
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting Rod ServiceConnecting Rod Service
• Inspection– Twists greater than 0.002 in. (0.05 mm) are
not acceptable – Some specialty shops can remove twist by
bending the rod cold
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting Rod ServiceConnecting Rod Service
• Inspection– Both cast and forged rods can be
straightened– Many engine builders replace the
connecting rod if it is twisted
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-36 A press used to remove the connecting rod from the piston.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-37 If the rod is twisted, it will cause diagonal-type wear on the piston skirt.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-38 A rod alignment fixture is used to check a connecting rod for bends or twists.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting Rod ServiceConnecting Rod Service
• Reconditioning Procedure– STEP 1: Parting surfaces of the rod and cap
are smoothed. A couple thousandths of an inch of metal is removed from the rod cap parting surface. The amount removed from the rod and cap only reduces the bore size 0.003 to 0.006 in. (0.08 to 0.15 mm).
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting Rod ServiceConnecting Rod Service
• Reconditioning Procedure– STEP 2: The cap is installed on the rod, and
the nuts or cap screws are properly torqued. The hole is then bored or honed to be perfectly round and of the size and finish required to give the correct connecting rod bearing crush.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Connecting Rod ServiceConnecting Rod Service
• Reconditioning Procedure– NOTE: Powdered metal connecting rods
cannot be reconditioned using this method. Most manufacturers recommend replacing worn powdered metal connecting rods.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-39 Rod bearing bores normally stretch from top to bottom, with most wear concentrated on the rod cap.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-40 To help ensure that the big ends are honed straight, many experts recommend placing two rods together when performing the honing operation.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PISTON AND ROD PISTON AND ROD ASSEMBLYASSEMBLY
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston and Rod AssemblyPiston and Rod Assembly
• Interference Fit Rods– Pin is put in one side of the piston– Check small end of connecting rod for
proper size
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston and Rod AssemblyPiston and Rod Assembly
• Interference Fit Rods– Small eye on connecting rod is heated
before pin is installed causing rod eye to expand
– Pin must be rapidly pushed into the correct center position
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-41 The small end of the rod is being heated in an electric heater and the piston is positioned properly so the piston pin can be installed as soon as the rod is removed from the heater.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston and Rod AssemblyPiston and Rod Assembly
• Full-Floating Rods– Full-floating piston pins operate in a
bushing in the small eye of the connecting rod
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston and Rod AssemblyPiston and Rod Assembly
• Full-Floating Rods– Bushings and pistons are honed to the
same diameter to allow the pin to slide freely through both
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston and Rod AssemblyPiston and Rod Assembly
• Full-Floating Rods– Pin is held in place with a lock ring at each
end– Lock rings expand into a small groove in
the pin hole
• NOTE: The original lock rings should always be replaced with new rings.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
PISTON RING SERVICEPISTON RING SERVICE
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ServicePiston Ring Service
• Steps– Check side clearance– Check ring gap– Install oil control ring
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Piston Ring ServicePiston Ring Service
• Steps– Install compression rings– Double-check everything
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-42 The side clearance of the piston ring is checked with a feeler gauge.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-43 The ring gap is measured using a feeler gauge.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-44 A hand-operated piston ring end gap grinder being used to increase the end gap of a piston ring so that it is within factory specifications.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-45 A typical ring expander being used to install a piston ring on a piston.
33 PISTONS, RINGS, AND CONNECTING RODS
Automotive Technology, Fourth EditionJames Halderman
© 2011 Pearson Education, Inc.All Rights Reserved
Figure 33-46 Identification marks used to indicate the side of the piston ring to be placed toward the head of the piston.
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