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Rebuilding the Chevy 3.4L/3.5L Engine

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(Download the illustrated pdf here)

We’re going to take a look at two of these engines, including both
versions of the latest 3.4L that was used in the Chevy Equinox (and
Pontiac Torrent) and the original 3.5L that was installed in several
’04-’07 Chevy cars and crossovers. And, we’ll give you an overview of
what to expect when you see the “late” 3.5L with variable valve timing
(VVT) that was introduced along with the 3.9L in 2006.

Let’s start with the ’05-’06 3.4L Equinox that was built in Shanghai,
China. GM called it RPO “LNJ”, but we know it as VIN code “F”. It
shared the same bore and stroke as the 3.4L that was used in the FWD
cars up through ’05, but it was updated in almost every possible way,
starting with the block.

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Blocks

The Equinox had a unique block that had four more bolt bosses on the
right side along with one more up high and two less above the pan rail
on the left side. There were three different castings including the
12503385 and 12575190 that were used in ’05 and ’06 and the 12599542
that was used from ’07 through ’09. The only difference in the later
block was the larger cam bore that was needed to accommodate the new 4X
cam that had bigger journals.

Cranks

The new crank for the ’05-’06 Equinox had a pressed-on sensor that had
24 notches instead of the earlier version that had seven notches
machined directly into a cast ring on the crank. This same casting, the
12575064, was used from ’07 through ’09, too, but the earlier,
two-piece, riveted reluctor wheel with 24 notches was replaced by a
one-piece, machined sensor wheel that had 58 notches. The additional
notches meant that the sensor inputs were faster and more accurate for
GM’s new, high-speed computer platforms. Just for the record, these
trigger wheels aren’t available separately from GM, so you will have to
buy a $400 crankshaft if you damage a sensor.

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Rods

The forged rods used in all the earlier 3.4L engines were replaced by
powdered metal rods with cracked caps for the Equinox. They shared the
same dimensions, but rebuilders will have to hone the big end oversize
in order to recondition the rods. That’s not a problem, though, because
the oversize O.D. rod bearings are already available in the
aftermarket. Look for GKN 8537 on the big end of the rod.

Pistons

Chevy updated the piston, too. It weighed the same as the earlier
design, but the ring pack was relocated and the bottom groove for the
oil ring was about 1.0 mm narrower. The OEM piston is a Mahle 92L62.

Cams

The ’05-’06 Equinox continued to use the 12567117 cam that had been
used since 2003 in both the 3.1L and 3.4L car engines. Look for the
wide, raised tab half-way around the cam and “7117” or “7165” on the
back of the rear journal for ’05 and ’06.

In ’07, Chevy switched to the 12596667 that had larger journals
(approximately 2.02? vs 1.87?) and four notches for the “4X sensor” and
continued to use it up through ’09 when this engine was discontinued.
It has “6567” etched on the back of the rear journal. GM added the “4X
sensor” to the cam to support the new E67 computer along with the 58X
crank sensor that was added in ’07.

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Timing Components

The Equinox has a new timing set that has a narrow chain and gears
along with a fixed chain guide. The chain measures 10.0 mm across the
links instead of the 14.0 mm and the gears are about 0.110? narrower.

Heads

GM continued to use the same head castings with the smaller water
outlets that were originally installed on the ’04-’05 3.1L and 3.4L car
engines, but with a couple of differences:

1) There’s a new 12575082 casting that’s the same as the 12580234
casting that was used on the earlier cars, but both of these castings
came with either 8.0 mm or 10.0 mm rocker bolts, so be sure to install
them in matching pairs.

2) Most, but not all, of the Equinox motors have a temp sensor located
on the back of the head on the passenger side, so most of the heads
have this additional hole, but it can cause problems whether or not
it’s drilled and tapped. Here’s why:

• The hole on the back of the head on the passenger side must be
drilled and tapped because it’s usually needed for the temp sensor, but
be sure to plug it just in case it’s not used for a particular
application.

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• If there’s a hole in the front of the head on the driver’s side, it
must be plugged, because it’s never used and it’s impossible to install
the plug once the front cover is on the engine and it’s in the car.

So, that’s the story on the 3.4L Equinox. It’s similar to the earlier 3.4L car engines, but with several important differences. Chart 1 gives a quick recap of the changes compared to the ’05 FWD car engines.

As you can see from that chart, the ’05-’06 Equinox was all new except
for the cam and heads, and by the time the cam was changed in ’07, the
heads were the only thing the Equinox shared with the earlier FWD cars.

With all that in mind, now let’s take a look at the 3.5L engine that
was introduced as the “LX9” in ’04 and used up through ’07 in the Buick
Rendezvous. It was a VIN code 8 or L and it came without the variable
valve timing that was added to the LZ4/LZE (VIN code K or N) that
showed up in ’06 along with the new 3.9L engine.

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The “LX9” was basically a bored version of the 3.4L Equinox, but the
cam and the timing set were the only two major components that were
shared by both engines.

Blocks

There’s only one block for the early 3.5L that was used from ’04
through ’07. It’s a 12581558 casting that has “3.5L” located right
beside the casting number. This block is unique because it has a few
more bolt bosses on the sides and a flat pad that’s machined on the
bottom of the main oil gallery for the piston oil cooler that sprays
oil up on the back two cylinders to “ensure even lubrication of the
cylinder walls” and “reduce noise.”

Cranks

The early 3.5L crank has “3.5L” cast right on the front rod throw and a
two-piece, riveted 24X crank reluctor wheel that’s pressed on a stepped
surface located between the #3 the #4 rod throw. It looks a lot like
the 3.4L Equinox crank and it shares the same 3.31? stroke, but the rod
journals are about 0.240? larger in diameter and edges of the small
counterweights are chamfered.

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Rods

The rod for the 3.5L is powdered-metal with a cracked cap, too, with
larger bores on both ends, but it’s slightly shorter between the edge
of the bores than the one that was used for the 3.4L. There is no ID
number on these rods, but there’s a raised “hump” across the cap beside
one of the rod bolts.

Cam

The 3.5L had the same 12567117 cam that GM had used in the 3.1L and
3.4L cars since 2003 and in the Equinox in ’05 and ’06. It has the
small journals (about 1.87?) and either “7117” or “7165” stamped on the
back of the rear journal.

Timing Components

The new, narrow chain and gears that were found on the early Equinox
were used on all the 3.5L motors. The chain is a p/n 24506090, the cam
gear is a p/n 24506089 and the crank gear is a p/n 12568125.

Heads

The head for the early 3.5L is unique to this application. It’s a
12578523 casting that looks similar to the ones found on the 3.4L
engines, but both the intake and exhaust ports were modified and the
chamber was revised, too, so they’re actually quite different when you
see them side by side. Just remember that there must be a hole for the
temp sensor on the back of the head on the passenger side, but don’t
leave an open hole in the front of the one on the driver’s side.

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That’s about all you need to know about how to identify the early 3.5L,
but there’s another 3.5L that was introduced in ’06 that shares 80% of
its components with the brand new 3.9L engine. It’s the RPO “LZ4/LZE”
motor that carries VIN code K or N and it’s used up through today.
Here’s what to expect when you see one:

Block – The late 3.5L shares an all new block with the
3.9L engine that comes with a 3.90? bore. It has piston oil cooling
jets on all six cylinders and casting provisions in the valley for the
“lifter oil management assembly” that was part of the “active fuel
management” (AFM) system that was added to the 3.9L engine when it was
used for the Impala starting in ’07. We have a 12577641 casting, but it
appears that there are three or four blocks with minor differences.

Crank – The late 3.5L crank has a 3.0? stroke with a
58X trigger wheel instead of the one with the 3.31? stroke with a 24X
wheel that was used on the early 3.5L. We believe that it’s a number
12579425 casting.

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Rods – They’re powdered metal with cracked caps, but
the length is different because GM combined the shorter stroke with the
same piston that was used in the 3.9L. The rod has the larger pin bore
because it’s bushed for a full-floating pin.

Pistons – The late 3.5L and the 3.9L share a common
piston. It’s a Mahle 99L16 casting with a small dish, four valve
reliefs and pin locks.

Cam – The late cam has the big journals, the “4X
sensor,” and provisions for variable valve timing, but the lift and
duration are unique to this particular application. It’s a 12591840
that has “1840” etched on the back of the last journal.

Timing Components – The timing chain and gears are the
only components that are the same as the ones that were used on the
early 3.5L, but there’s a new tensioner that replaces the old chain
guide.

Variable Valve Timing – The big change in the “late”
3.5L was the addition of variable valve timing (VVT). “This system
incorporates a vane-type cam phaser that changes the angular
orientation of the camshaft, thereby adjusting the timing of the intake
and exhaust valves to optimize performance and economy and helping to
lower emissions,” according to GM. The cam has bigger journals and a
“4X sensor” and it’s unique to this application. The front cover has a
“black box” with a computer controlled “magnet” that pushes on a valve
that’s located in the middle of the cam phaser. It in turn applies oil
pressure to either side of the vanes to advance or retard the cam in
real time. It can advance the timing up to 15 degrees or retard it as
much as 25 crankshaft degrees to “optimize performance and economy.” GM
claims a fuel savings of up to 3% with VVT. It also eliminates the need
for an external EGR system because it gets all the EGR it needs by
retarding the cam and increasing the overlap. It’s pretty high-tech for
a pushrod V6, but it works fine and does a good job.

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Heads – The heads are all new and shared with the
3.9L. They have big intake ports, modified chambers with bigger valves
and updated exhaust ports. And, the water outlets were moved from the
intake surface to the front of the heads. We know of two castings, the
12590746 and 12624610 that come with or without holes drilled for
A.I.R.

Head Gaskets – The late 3.5L has MLS head gaskets instead of the Grafoil ones that were used on the ’07 3.5L without VVT.

All in all, it’s a whole new engine that we will research in more
detail when cores and parts become more readily available. Meanwhile,
just be aware that both engines were used in ’06 and ’07 and verify the
VIN number and application before selling one or the other.

Conclusion

That’s the story on the 3.4L Equinox and the early 3.5L. GM continues
to build some of the best pushrod motors in the world. The LS motors
are well respected and so are the “high value” V6s including the 3.4L,
3.5L and 3.9L. The level of sophistication in these little motors is
amazing, especially when you take a look at the 3.9L with variable
valve timing AND active fuel management, all working together to
provide good performance and economy along with low emissions. It’s an
amazing feat of technology that will soon be showing up in all our
shops.

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Doug Anderson is Manager of Technical Services for
Grooms Engines, located in Nashville, TN. He has authored numerous
technical articles on engine rebuilding for Engine Builder magazine for
more than 20 years. Anderson has also made many technical presentations
on engine building at AERA and PERA conventions and seminars.

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