I6 4.0 Part 03 Pistons and Rods.pdf
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20898 KB
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Pobierz
MOPAR PERFORMANCE PARTS
148
Connecting
Rods
5.
The connecting rod bearing clearance is 0.25-0.76 mm
(0.001-0.003"). Preferred bearing clearance is
0.044-
0.050 mm (0.0015-0.0020").
INTRODUCTION
The 4.0L engine's connecting rods are made of cast
malleable iron with a total weight (less bearings) of 657-
665 grams (23.2-23.5 oz.), and a total length (center-to-
center) of 155.52-155.62 mm (6.123-6.127").
Connecting rod bore diameter (less bearings) is 56.09-
56.08 mm (2.2085-2.2080").
For
more connecting rod specifications,refer to
4.0LEngine
Specifications,
'Engine Assembly' section of this chapter.
6.
The connecting rod bolt head should be seated against
the flat, machined surface in the connecting rod.
7.
For a race engine, the big end of the connecting rod
should be sized to the minimum diameter to get the
maximum crush from the bearing.
8.
Shot-peening the rods is recommended if they haven't
been already.
Connecting Rod
These heavy duty forgings are shot-peened and Magna-
fluxed. Includes high strength bolts. Can be used as heavy
duty stock replacement. For 2.5L
and
4.0L engines only.
(Sold individually.)
P4529209
9. Some race engines use floating piston pins. On these
engines, the pin-to-connecting rod clearance should be
checked. On standard production engines that use a
pressed pin, the amount
of
interference should be
checked. (Refer to
4.0L
Engine Specifications,
'Engine
Assembly' section of this chapter.)
10. Connecting rods with full floating pins to be used in
racing applications should have the small end of the
connecting rod drilled with a 'small hole
(approximately 3/32") for increased piston pin oiling.
The best location for this oiling hole is the top of the
connecting rod above the pin (Figure 4-11). Pin oiling
holes in the sides (5 o'clock
or
7 o'clock, for example)
weaken the connecting rod itself and therefore are
NOT recommended. One hole in the top does the best
job
of
oiling the pin and maintaining the connecting
rod's strength.
Connecting rod.
Connecting Rod Bearings
These connecting rod bearings are made of production-
style material. Available in standard and two undersizes.
For Jeep 2.5L and 4.0L engines only. (Sold individually.)
P4529208
Connecting rod bearings, standard size.
P4529236
Connecting rod bearings ,.001" undersize.
P4529238
Connecting
rod
bearings,
.010"
undersize.
BASIC CONNECTING ROD PREPARATION AND
INSTALLATION TIPS
Note:
The' following information is for the preparation of
steel connecting rods only.
1.
Piston Pin Oiling Hole
Piston Pin
Centerline
Connecting rods should be checked for alignment; bores
should be parallel. Check big and small ends for size.
2.
Using a small file, deburr the connecting rods, paying
particular attention to the mating surfaces and tab
groove. You need the clamping effect of a 60 micro
bore. The sides should be polished by hand on a flat
plate using #600 paper. Proper side clearance should be
0.25-0.48 mm (0.010-0.019'').
DO
NOT increase side
clearance past .019" as this increases the oil demand of
the engine. It will also allow too much oil on the
cylinder walls which will overload the rings and allow
excess oil in the combustion chambers.
Figure
4
-
11
In an engine that is to be used in a high rpm situation,
the connecting rods and connecting rod bolts should be
Magna-Glo checked for cracks or forging flaws.
3.
4.
A race engine should always use heavy duty
connecting rod bolts and nuts.
-
SPECIAL CONNECTING ROD INSTALLATION
PROCEDURES
4.0L POWER TECH IN-LINE
6
(CONNECTING
RODS)
149
Since we (Mopar Performance Parts) are in the parts
business, we should have an answer to this question. After
all, there are no numbers stamped on the side of service
connecting rods or Mopar Performance Parts connecting
rods (or any aftermarket connecting rod for that matter).
Therefore, the numbers can’t be used to tell us why. Does
this mean that the caps can be reversed? How about on a
service connecting rod? The answer
is
still “N
O
!” We’ll
have to look deeper to find out why.
Connecting rod cap tab slots are a feature that you may
think will lead to the “why?’ answer. There is a slot in the
cap and one in the connecting rod that align the bearing
shells. These two tabs (or slots) have to be together. This
would mean that the two slots would be next to the same
bolt. Although this
is
true, it is NOT the complete answer.
(It ‘isonly coincidence!)
If you take the cap off the connecting rod assembly, you
will notice that there is a V-groove across the parting face
of the cap. You will note that the V-groove is on the
opposite side from the bearing tab slot. There is also a small
V-notch in the bearing shell which should be installed to
line up with the V-groove in the cap. This groove provides
lubrication of the cylinder wall on the opposite bank. We’re
getting warmer!
In racing and other very high performance engines, the
connecting rod caps may not have
a
V-groove. Extremely
high rpm applications don’t need any more oil on the
cylinder walls,
so
the V-groove may be omitted. Even
though the V-groove isn’t always there, the fact that it is
designed to oil the opposite wall leads us to the correct
answer. The groove-to-wall relationshipmeans that how the
connecting rod fits into the crankcase is important.
The key to all of this is to notice that the chamfer on the big
end of the connecting rod is not the same on both sides.
There is a big chamfer on one side and a small chamfer on
the other. The big chamfer goes toward the crankshaft while
the small chamfer goes toward the other connecting rod. If
the cap gets reversed, then there would be a small chamfer
on the connecting rod and a large chamfer on the cap. This
is how you can tell that a cap had been reversed. DO NOT
assume that a used engine did not have some of its caps
reversed. The proper way to install the connecting rod into
the engine is that the right cylinder bank
(#2,
4,
6)
should
have the large chamfer toward the rear of the engine. The
connecting rods on the left bank (#l, 3, 5) should have the
large chamfer toward the front of the engine. The service
manual ties the direction of the chamfer to the “notch” in
the top of the piston. In racing we may reverse the pistons
or have no offset and therefore no notch
or
arrow. Therefore
it is best to install connecting rods by chamfer and cylinder
location. The service manual also says that
YOU
should fit
all connecting rod and piston assemblies on one bank until
complete. This
is
important. DO NOT alternate from one
bank to another.
Rod
Ratio
For all-out modified race engines, it is recommended that a
rod ratio (length of the rod divided by the stroke) of 1.75 to
1.85
be maintained if possible for best performance. (The
stock 4.0L engine has a rod ratio of 1.78-this is considered
the best overall choice.) Side clearance should be 0.25-0.48
mm (0.010-0..01911).
Measuring
Side
Clearance
Slide snug-fitting feeler gauge between the connecting rod
and crankshaft journal flange. The correct clearance is
0.25-0.48 mm (0.010-0.019’1). DO NOT increase
connecting rod side clearance (two rods) beyond
specifications. Replace the connecting rod if the side
clearance is not within specification.
Note:
Excessive side clearance increases the oil demand of
the engine as a result of excessive oil leakage past the
connecting rods. Increasing oil demand reduces the oil
available for lubrication and cooling at high engine speeds.
Excessive side clearance also increases the amount of oil
sprayed on the cylinder walls overloading the
oil
rings.
The excessive oil then ends up in the combustion
chamber and can cause pre-ignition. (By definition, oil is
a very low octane fuel!)
Cap Alignment
Sometimes the simplest questions can be the hardest to
answer. In some cases you assume that everyone knows the
answer already. For example, someone asks the question,
“Can you reverse the cap on a connecting rod?” The answer
is, “No!” Although this is correct, the follow-up question
(“why?”) is not so easy to answer. During engine assembly
we line up the numbers
on
the sides of the connecting rods.
Therefore, if we reversed the caps, the numbers would not
line up. Sounds good, but is it the complete answer?
i
150
MOPAR PERFORMANCE PARTS
We began this discussion trying to find out how to tell if a
cap had been reversed. We now know how to locate the cap
and how to install the connecting rod assembly in the
engine. These two items are closely related because the
method of determining main cap orientation and the key to
installing connecting rods are the same. It is important to
know both because once the connecting rod and piston are
assembled, the cap still has to be removed one more time to
get the connecting rod on to the crankshaft. One more
chance to reverse the cap or the connecting rod. Our main
check on the assembly at this point is usually the valve
notch on the top of the piston. However, it is also a good
idea to double check the chamfer-crankshaft relationship
after the connecting rodpiston installation to verify that a
cap didn’t get reversed in the last step.
tipped on its side. This makes slipping’the connecting rod,
piston and ring assembly into the block easier. In this
configuration, the long protector should go over the top of
the connecting rod journal. Before you make an error,
remember that the piston MUST be installed into the block
in its proper orientation for pin offset, valve notches, etc.
So
the first task is to determine this orientation BEFORE you
install the connecting rod bolt protectors. Now put the long
protector on the top bolt as installed. Somewhat confused?
Now you can see why using two long protectors might be
easier to work with and is the recommended choice.
As soon as the piston and connecting rod assembly is seated
against the crankshaft journal, the connecting rod bolt
protectors are removed.
ALUMINUM CONNECTING RODS
Connecting
Rod
Bolt Protectors
In every engine assembly or build-up, the piston and
connecting rod assembly must be installed into the block
and on to the crankshaft. During this phase of engine build-
up, the connecting rod bolts have to be protected. This is
because when the connecting rod cap is removed to allow
for the installation of the connecting rod and piston
assembly and the bearing shells, the connecting rod bolts
pressed into the connecting rod are left sticking out
unprotected. Aluminum connecting rods have the
connecting rod bolts threaded into the connecting rod beam
and are, therefore, one of the few exceptions to this
condition. In any case, the bolts that stick out must be
protected during installation.
To protect the bolts, cover the connecting rod bolt threads.
There are several choices for protectors. The “Pros” tend to
use threaded brass rods. Another option is simply a piece of
rubber fuel line. Our favorite is neoprene (clear plastic)
line. Lengths are somewhat optional, but should be at least
9”
-
12” long for the top bolt. The second piece, for the
bottom bolt, could be as short as
3”
-
4”
long, but 9”
-
12”
long is recommended.
The main reason the threads need to be covered is to protect
the crankshaft journal during piston-connecting rod
installation. If you don’t use protectors, it’s very easy to
scratch the connecting rod journal with the end or threads
of the connecting rod bolt. Crankshafts are much more
expensive to repair or replace than connecting rod bolts.
A secondary function of connecting rod bolt protectors is to
guide the connecting rod over the crankshaft journal during
installation. This is only true if you use at least one long
protector. If you use short ones (or none at all), then the
connecting rod can easily end up on the wrong side of the
journal, which can result in other damage.
The proper procedure for installing the connecting rod and
piston assembly begins with.the crankshaft’s rod throw at
the bottom of its travel, or BDC (Bottom Dead Center).
Generally, the cylinder that you are working on should be
Note:
Aluminum connecting rods should be used ONLY in
conjunction with lightweight pistons.
Aluminum connecting rods are a race-only piece. Although
most standard production connecting rods are designed for
pressed-pins, most race pistons are designed for full
floating pins. When building a race engine, the pistons
would generally be replaced before the connecting rods.
For an all-out race engine there are advantages to the full
floating pin. (Be sure to check pin clearance in the
connecting rod upon assembly.)
If you broke a steel connecting rod, you’d probably buy a
new one, rebuild it and put everything back together.
Aluminum connecting rods aren’t quite that easy. (By
“breaking” we mean a partial failure like a scuffed big end,
overheated, bent or nicked from handling. If the connecting
rod breaks in two, there won’t be much left to “put back
together.”)With aluminum connecting rods, if you drop one
and nick it, you can replace it with a new one. However, if
after several runs you scuff it, overheat it, bend it, etc., you
don’t want to just replace it. Your best bet is either to
replace all six connecting rods or to send the five good
pieces back to the manufacturer and have them “rebuilt”
and matched to the sixth. We strongly recommend keeping
any instruction sheet or other manufacturer information that
might come with your specific set of connecting rods to
help you contact the manufacturer at a future date.
The main advantage of aluminum connecting rods is their
lighter weight. However, they do require some special
considerations. These special considerations are primarily
clearances, which may be slightly different from steel
connecting rod numbers. These differences can be
important. Be sure to check with the manufacturer for
correct specifications.
4.0L POWER TECH IN-LINE
6
(CONNECTING RODS)
151
CONNECTING ROD BEARINGS
6. Install bearing cap and connecting rod on the journal
and tighten nuts to
45
Nom
(33
ft-lbs) torque.
DO
NOT
rotate crankshaft. Plastigauge will smear, resulting in
inaccurate indication.
7. Remove the bearing cap and determine the amount of
bearing-to-journal clearance by measuring the width of
compressed Plastigauge by using the scale on the
Plastigauge envelope (Figure 2-16). The correct
clearance is 0.025 to 0.076 mm (0.001 to 0.00311).
Plastigauge should indicate the same clearance across
the entire width of the insert. If the clearance varies, it
may be caused by either a tapered journal, bent
connecting rod, or foreign material trapped between
the insert and cap or rod.
8. If the correct clearance is indicated, replacement of the
bearing inserts
is
not necessary. Remove the
Plastigauge from crankshaftjournal and bearing insert.
Proceed with installation.
9.
If bearing-to-journal clearance exceeds the
specification, install a pair of 0.0254 mm (0.001")
undersize bearing inserts.
All
the odd size inserts must
be on the bottom. Service replacement bearing insert
sizes are stamped on the backs of the inserts. Measure
the clearance as described in the previous steps.
10.
The clearance measured with a pair of 0.0254
mm
(0.00ll') undersize bearing inserts installed will
determine if two 0.0254 mm
(0.001")
undersize inserts
or another combination is needed to provide the correct
clearance. (Refer
to
Connecting Rod Bearing Fitting
Chart
[Figure 4-15].)
Example:
If the initial clearance was 0.0762
mm
(0.003"), 0.025 mm (0.001") undersize inserts would
reduce the clearance by
0.025
mm
(0.001"). The
clearance would be 0.002" and within specification.
A
0.051 mm (0.00211)undersize insert would reduce the
initial clearance an additional 0.013 mm
(0.0005").
The clearance would then be 0.038
mm
(0.0015").
11. Repeat the Plastigauge measurement to verify your
bearing selection prior to final assembly.
12. Once
you
have selected the proper insert, install the
insert and cap. Tighten the connecting rod bolts to 45
Nam (33 ft-lbs) torque.
For racing purposes there are two special connecting rod
bearings materials used: Babbit and Tri-Metal. In general,
Tri-Metal is preferred for oval track racing, Babbit for drag
racing.
Installation
Fit all connecting rods on one cylinder bank until
completed. DO NOT alternate from one bank to another,
because when the rods are assembled to the pistons
correctly, they are not interchangeable from one bank to
another.
The bearing caps are not interchangeable and should be
marked at removal to ensure correct assembly.
Each bearing cap has a small V-groove across the parting
face. When installing the lower bearing shell, make certain
that the V-groove in the shell is in line with the V-groove
in the cap. This provides lubrication of the cylinder wall in
the opposite bank.
The bearing shells must be installed
so
that the tangs are in
the machined grooves in the rods and caps.
Limits of taper or out-of-round on any crankshaft journals
should be held to 0.0254 mm (0.001"). Bearings are
available in 0.025
mm
(O.OOll'), 0.051
mm
(0.00211),0.076
mm (0.00311),0.254
mm
(0.010") and 0.305 mm (0.012")
undersize. (Contact your local Chrysler-Plymouth-Dodge-
Jeep dealer for ordering information.)
Note:
Install connecting rod bearings in matched pairs.
DO
NOT use a new bearing half with an old bearing half.
DO
NOT file the rods or bearing caps.
Measuring Connecting
Rod
Bearing Clearance
1.
Wipe the journal clean of oil.
2.
Use short rubber hose sections over rod bolts during
installation.
3.
Lubricate the upper bearing insert and install in
connecting rod.
4.
Use a piston ring compressor to install the rod and piston
assemblies with the oil squirt holes in the rods facing the
camshaft and the arrow on the piston crown pointing to
the front of the engine (Figure 2-37). Verify that the oil
squ& holes in the rods face the camshaft and that the
arrows on the pistons face the front of the engine.
5.
Install the lower bearing insert in the bearing cap. The
lower insert must be dry. Place a strip of Plastigauge
across the full width of the lower insert at the center of
bearing cap. Plastigauge must not crumble in use. If
brittle, obtain fresh stock.
152
MOPAR PERFORMANCE PARTS
Pistons
and
Rings
Cast Pistons and
Rings
for Jeep 4.0L Engines
Bore
Stroke
Rod
CR
Dome
Part Number
Rings
9.2:l
I
Dish
I
P4876961
I
I
I
3.41"
I
I
P4876962
3.905"
6.125"
In an effort to help clarify this situation and help racers
know what they are basically getting, most piston
manufacturers rate their pistons by compression ratio.
To
do this, they assume that the engine is, at blueprint
or
nominal
specifications.
For
example, Mopar Performance
Parts has a line of 9.2:l pistons. If your engine had a
nominal compression ratio of 8.2:l from the factory and
you
installed these pistons, then you would have
a
9.2:l
compression ratio.
The confusion comes in because most engines don't have
the actual nominal compression ratio. It might be 8.2: 1. It
might be
8.0:
1,
or
possibly 7.8:l.
If
your engine really has
a 7.8:l compression ratio and you install 9.2:
1
pistons,
you'll actually have an 8.8:l compression ratio. The piston
is
only one of many factors that contribute to the exact
compression ratio. There is cylinder head volume (cc) and
gasket thickness. There is also the deck height which takes
into account connecting rod length. changes, stroke
variations, and block height machining tolerances. (Valve
notches, chamfers, dish/dome volumes, and pin height are
assumed to be
part
of the piston.)
So when you change the piston design and move the pin
down to increase the compression ratio (or add
a
dome),
you are only changing the piston. Let's assume that the
deck tolerances are .020" to .030" below the cylinder head,
and the cc range is from 68 to 72. The piston itself can't
change variations in these other parts. On any given engine,
the difference is between the rated compression ratio for the
pistons and the engine's actual nominal compression ratio.
For example, if the engine's actual nominal compression
ratio is 8.2: 1, then 9.2:l pistons increase the compression
ratio one point (9.2
-
8.2
=
1).
Therefore, if the engine's
actual nominal compression ratio is 7.8:1, then the resulting
compression ratio after installing 9.2:l pistons is
8.8:l.
The
only way to determine if your engine has
an
8.2:l or 7.8:l
compression ratio is to measure it. This requires you to cc the
heads, measure the deck heights with a micrometer or similar
device, and check the compressed thickness of the gaskets.
All pistons share this problem.
If
you don't make the required
measurements, you won't ever know you're exact compression
ratio. And there are still other variations. The only way to
remove
all
these variations is to blueprint the engine.
PISTONS
The 4.0L engine uses high strength aluminum alloy pistons
with an anodized top ring groove and crown. Piston skirts
are coated
with
a solid lubricant (Molykote) to reduce
friction and provide scuff resistance.
A
pressed
fit
piston pin
is used to attach the piston and connecting rod. The piston
combustion cavity is
a
single quench design. For more
piston (and piston ring) specifications, refer to
4.OL
Engine
Specifications,
'Engine Assembly' section of this chapter.
In summary, the secret with pistons is that they be
lightweight and have smooth, round tops
if
they are domed.
The secret with piston rings is to get them to seal to the
piston and the bore at W.O.T. (wide open throttle).
Piston Compression Ratio Ratings
Pistons are usually described by their bore
or
overbore size
and their rated compression
ratio.
This compression ratio
rating seems to get people confused. Generally there are
8.0:1,
9.0:l.
10.5:1,
ll.S:l,
and even 12.5:l pistons. There
are dished and domed pistons. Generally domed pistons
have a high compression ratio rating and dished pistons
have a low compression ratio rating. However, the piston
doesn't have a compression ratio by itself. It has to be
installed into an engine.
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