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(Download the illustrated pdf here)

We’re going to take a look at two of these engines, including bothversions of the latest 3.4L that was used in the Chevy Equinox (andPontiac Torrent) and the original 3.5L that was installed in several’04-’07 Chevy cars and crossovers. And, we’ll give you an overview ofwhat 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”. Itshared the same bore and stroke as the 3.4L that was used in the FWDcars up through ’05, but it was updated in almost every possible way,starting with the block.

Blocks
The Equinox had a unique block that had four more bolt bosses on theright side along with one more up high and two less above the pan railon the left side. There were three different castings including the12503385 and 12575190 that were used in ’05 and ’06 and the 12599542that was used from ’07 through ’09. The only difference in the laterblock was the larger cam bore that was needed to accommodate the new 4Xcam that had bigger journals.

Cranks
The new crank for the ’05-’06 Equinox had a pressed-on sensor that had24 notches instead of the earlier version that had seven notchesmachined directly into a cast ring on the crank. This same casting, the12575064, was used from ’07 through ’09, too, but the earlier,two-piece, riveted reluctor wheel with 24 notches was replaced by aone-piece, machined sensor wheel that had 58 notches. The additionalnotches meant that the sensor inputs were faster and more accurate forGM’s new, high-speed computer platforms. Just for the record, thesetrigger wheels aren’t available separately from GM, so you will have tobuy a $400 crankshaft if you damage a sensor.

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

Pistons
Chevy updated the piston, too. It weighed the same as the earlierdesign, but the ring pack was relocated and the bottom groove for theoil 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 beenused since 2003 in both the 3.1L and 3.4L car engines. Look for thewide, raised tab half-way around the cam and “7117” or “7165” on theback 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” andcontinued 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 “4Xsensor” to the cam to support the new E67 computer along with the 58Xcrank sensor that was added in ’07.

Timing Components

The Equinox has a new timing set that has a narrow chain and gearsalong with a fixed chain guide. The chain measures 10.0 mm across thelinks 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 wateroutlets that were originally installed on the ’04-’05 3.1L and 3.4L carengines, but with a couple of differences:

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

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

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

• If there’s a hole in the front of the head on the driver’s side, itmust be plugged, because it’s never used and it’s impossible to installthe 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 exceptfor the cam and heads, and by the time the cam was changed in ’07, theheads 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 thatwas introduced as the “LX9” in ’04 and used up through ’07 in the BuickRendezvous. It was a VIN code 8 or L and it came without the variablevalve timing that was added to the LZ4/LZE (VIN code K or N) thatshowed up in ’06 along with the new 3.9L engine.

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

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

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

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

Cam
The 3.5L had the same 12567117 cam that GM had used in the 3.1L and3.4L cars since 2003 and in the Equinox in ’05 and ’06. It has thesmall journals (about 1.87?) and either “7117” or “7165” stamped on theback of the rear journal.

Timing Components
The new, narrow chain and gears that were found on the early Equinoxwere used on all the 3.5L motors. The chain is a p/n 24506090, the camgear 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 a12578523 casting that looks similar to the ones found on the 3.4Lengines, but both the intake and exhaust ports were modified and thechamber was revised, too, so they’re actually quite different when yousee them side by side. Just remember that there must be a hole for thetemp sensor on the back of the head on the passenger side, but don’tleave an open hole in the front of the one on the driver’s side.

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% ofits 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 the3.9L engine that comes with a 3.90? bore. It has piston oil coolingjets on all six cylinders and casting provisions in the valley for the“lifter oil management assembly” that was part of the “active fuelmanagement” (AFM) system that was added to the 3.9L engine when it wasused for the Impala starting in ’07. We have a 12577641 casting, but itappears that there are three or four blocks with minor differences.

Crank – The late 3.5L crank has a 3.0? stroke with a58X trigger wheel instead of the one with the 3.31? stroke with a 24Xwheel that was used on the early 3.5L. We believe that it’s a number12579425 casting.

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

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

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

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

Variable Valve Timing – The big change in the “late”3.5L was the addition of variable valve timing (VVT). “This systemincorporates a vane-type cam phaser that changes the angularorientation of the camshaft, thereby adjusting the timing of the intakeand exhaust valves to optimize performance and economy and helping tolower 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 valvethat’s located in the middle of the cam phaser. It in turn applies oilpressure to either side of the vanes to advance or retard the cam inreal time. It can advance the timing up to 15 degrees or retard it asmuch as 25 crankshaft degrees to “optimize performance and economy.” GMclaims a fuel savings of up to 3% with VVT. It also eliminates the needfor an external EGR system because it gets all the EGR it needs byretarding the cam and increasing the overlap. It’s pretty high-tech fora pushrod V6, but it works fine and does a good job.

Heads – The heads are all new and shared with the3.9L. They have big intake ports, modified chambers with bigger valvesand updated exhaust ports. And, the water outlets were moved from theintake surface to the front of the heads. We know of two castings, the12590746 and 12624610 that come with or without holes drilled forA.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 moredetail when cores and parts become more readily available. Meanwhile,just be aware that both engines were used in ’06 and ’07 and verify theVIN 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 continuesto build some of the best pushrod motors in the world. The LS motorsare 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 isamazing, especially when you take a look at the 3.9L with variablevalve timing AND active fuel management, all working together toprovide good performance and economy along with low emissions. It’s anamazing feat of technology that will soon be showing up in all ourshops.

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

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Doug Anderson

Doug Anderson

Manager of Technical Services at Grooms Engines
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.