PROJECT LS2, PART 1
We examine the block.
by Mike Mavrigian
all photos by author
Our new LS2 aluminum bare block was purchased from Scoggin-Dickey Parts Center. It arrived via UPS in a wood crate.
We’re starting this project build using a new LS2 aluminum block purchased from Scoggin-Dickey Parts Center. The LS2 block features a 4.002″ non-Siamesed bore that we’ll hone out, likely 0.020″ or 0.030″ oversize (the folks at Scoggin-Dickey recommend a max of 0.020″ overbore, while GM Performance suggests a max of 0.030″ overbore). In OE form, this is a 6.0L (364 CID) engine. Of course, we plan to bump displacement up a bit.
According to GM, the cylinder liners were designed for a stock stroke of 3.622″ and stroker combinations should be limited to “around” 4.000″. Depending on our piston design, we plan to stroke to either 4.000″ or 4.125″.
All LS series blocks feature 6-bolt mains (four vertical and two side bolts each), 9.24″ deck height, 4-bolt-per-cylinder head bolt pattern, standard GM bellhousing bolt pattern, 4.40″ bore spacing and 0.842″ lifter bore diameters. The thrust
bearing is located at the center bearing location.
Our block, although listed as “new,” looked like it had been through a battle-dings, nicks, scratches, scrapes, etc. The as-cast aluminum surfaces also had a distinctive brown tinge, like it had been stored in a dirty warehouse uncovered. No biggie since we’ll wash and clean up the various boogers.
I measured our block just to see where we were as compared to OE specs. The deck height varied by about 0.008″ (taller on the left bank). Cylinder bores measured, on average, 3.998″. During bore gauge checking, no discernible out-of-roundness or taper was found, so that was nice. One very noticeable oops that we found was evidence of an apparent casting core shift, as several cylinder liners were thin on one side and thick on the opposite side (front to rear). Basically, it looked as though the core shifted about 0.045″ with the liners then factory-bored on true center. As a result of a few thin liner walls, we’ll need to be careful when it comes to overboring. We may not be able to go much over the OE spec of 4.000″.
I could be wrong, but my guess is that these new bare blocks that are sold to the
aftermarket are units that didn’t pass muster during factory inspections. It’s not that big of a deal as all of the glitches we found are easily correctable. The only thing that bothered me was all of the surface scratches on machined surfaces,
especially on the front timing cover mating surfaces, and an out-of-round starter bolt hole, the obvious result of the boss being smacked (maybe the block was dropped on the floor at some point). But, again, this is easily fixable by running a drill through the hole.
Note: The rear of the block features drilled and tapped holes to accommodate late model bellhousings. Old style bellhousings can be installed, but a blank boss on the upper right side of the block’s rear face must be drilled and tapped. Why GM didn’t go ahead and perform that job is beyond me. The blank boss is already in the casting. I’ll need to install a bellhousing to provide an index point and I’ll drill/tap that hole to 10mm x 1.5 before the short block is assembled.
We also noticed that the top of the cam bearings were slightly damaged, resulting in an out-of-round condition at the cam bearing inner diameters. My guess is that someone along the line inserted a bar through the cam tunnel to lift/move the block. Since we plan to perform machining on this block, this doesn’t present a problem; we’ll need to remove these original cam bearings to properly wash the block anyway.
LS2 BLOCK INFO
GM P/N 12568950 available from Scoggin-Dickey for a suggested retail price of $999.99
This LS2 6.0L block is considered a Gen IV block, which is basically the same block with minor changes as compared to the LS1 and LS6 5.7L Gen III blocks. The cam position sensor has been moved to the front timing cover and there is no knock sensor provision in the engine valley. The LS2 features a knock sensor location on the side of the block.
This block is a direct replacement for 2005-2007 LS2 Corvette, SSR, GTO 6.0L and Trailblazer SS.
The block is cast from 319-T5 aluminum and features iron sleeves, 6-bolt iron main bearing caps, a (supposed) 9.240″ deck height and 4.00″ cylinder bores. This block will accept LS1, LS6, LS2, L92 or LS3 cylinder head designs.
BLOCK VALLEY AND COVER PLATE
Note: The LS2 block upper valley features a series of tower bosses with oil holes drilled through to the crankcase. In case you wondered what purpose these serve, these drilled towers were part of the original LS casting for engines that used GM’s displacement on demand system. On the LS2 block, these serve no purpose at all. The LS2 valley cover underside features o-rings that simply seal these towers off. Also, you may notice that the LS2 valley cover features a raised boss that’s drilled and tapped. This hole accepts the oil pressure switch. The underside of the cover plate also features a large and lumpy black plastic housing, feeding to a metal tube on the top side of the cover. This is for the PCV system.
BLOCK COMPLETION KIT
If you don’t have an LS engine core lying around, you’ll start off with a bare block. Since a bare block is, well, bare, even if you plan to use all aftermarket components, you still need a few OE-only parts. The thoughtful folks at Scoggin-Dickey recognized this need, so they assembled a “block completion kit,” P/N KITLS2CK-1, that includes:
BUT WAIT, THERE’S MORE
When the above kit arrived, I discovered that I didn’t have the camshaft plate or the rear seal housing. Upon contacting SDPC, I discovered that these parts are to be ordered separately (no big deal, somebody assumed I had an LS1 or LS6 block from which I could scavenge parts). I just wanted to point this out because if you don’t have a donor core from which to steal stuff, you’ll need everything I’ve listed here.
(Differences and interchangeability of parts)
Note: When using an OE LS2 block, be aware:
• LS2 blocks feature the knock sensor on the side of the block, while LS1 and LS6 blocks feature the knock sensor in the lifter valley.
• The LS2 cam sensor has been moved to the timing cover location, which requires the use of the LS2 cam gear.
• LS2 knock sensors are dedicated for LS2 and are not interchangeable with LS1/LS6 knock sensors.
• An LS1 engine-management computer will control an LS2 engine.
• LS2 blocks feature an original 4.00″ bore, while LS1/LS6 blocks feature a 3.898″ bore.
• Crankshafts, connecting rods, pistons and cylinder heads are interchangeable between LS2 and LS1/LS6 engines.
• LS2 cylinder heads are made from the same raw castings as LS6 heads.
BLOCK FASTENER SIZES
MAIN CAP FASTENER TORQUE VALUES (OE)
Note: Always follow the same sequence when tightening main cap fasteners. Follow the same sequence each time the caps are tightened (test fitting, final fitting, final assembly, etc.) to avoid altering bearing clearances. Also, be sure to always use the same torque wrench to avoid variables that could affect bearing clearance. Note that in some cases, a small threaded spreader bar (right- and left-hand threads with turnbuckle) may be needed to slightly expand the block sides to accommodate main cap removal without damaging the main cap to block mating surfaces. In our case, all caps removed easily by hand by gently rocking them fore/aft. A spreader bar may be more commonly needed when servicing the caps in a block where the 8mm main cap side bolts had once been torqued. By the way, the main cap bolts (inners feature a conventional hex head, while outers include a protruding stud for pan baffle mounting) are 10mm x 2.0 (very rough pitch). The inner bolts are 100mm long and the outers are 85mm long.
Note: Because GM reportedly individually fits each bearing (bearing-matching per individual engine), when you plan to use aftermarket main bearings, carefully measure the bearing thickness and crankshaft journals, and align-hone the main bore as needed to achieve proper bearing oil clearance.
I’ve heard that some builders tighten using torque-only, applying 60 lbs./ft. to the inner bolts and 50 lbs./ft. to the outer stud nuts. If you’re
using new OE fasteners, follow the torque-plus-angle method. If using aftermarket fasteners, adhere to the values recommended by the fastener maker.
In our next issue, we’ll complete the short block by fitting our crank, rods and pistons.
This will include checking bearing clearances, sizing bores for our pistons, performing any stroker clearancing that might be needed and balancing the rotating assembly