continued article by Richard Ehrenberg:
The Bottom End
Virtually all dimensions of the cast-iron block are new. The bore
spacing is reduced from the 1955-1998 small block's 4.46 to 4.09" - this an
indicator of how large the new engine eventually could (or could not) be
enlarged to. Basic bore size is 3.66," larger yes, than a 273 (by a mere
0.030) but smaller than all the other A-engines - the 318, even going back
to the 1950s, was always 3.9." Why ? Small bores are easier to clean up
for emissions. Speaking of bores, the roundness is held to a maximum of
0.00015", and taper to 0.0006" - virtually race engine specs.
Deck height is 9.09," compared to 9.60 for the ol'LA mill. As a even
more profound indicator of jest how new the new design really is, even the
offset of the LH cylinder bank is reduced.
Like the current LA-based V10, the 287 doesn't use individual main-bearing
caps. Instead, what Chrysler calls a 'bedplate' (girdle to us old
hotrodders) clamps all five mains at once, adding rigidity while reducing
noise and vibration. The bedplate is high-tech even to the material -
compacted graphite iron. It is sealed to the block with the old stanby:
RTV silicone sealer. Incidently, this bedplate is such a beefy piece that
disassembly is almost like 'splitting the cases' on a motorcycle engine.
The crankshaft is nodular cast iron, hardened and microfinished. A one
piece rear main seal, similar to the 2.2L design, seals to the outside of
the 100mm o.d. rear flange, which is an 8 bolt, one-offset pattern, in
Chrysler performance tradition. Main journals are 2.5" diameter, identical
to the 318/340 (the 360 is 2.81"), and are crossdrilled. Rod journals are
2.0", 1/8" smaller than the 318's 2.125. All journals have rolled fillets,
a significant step taken, in the best racing engines, to prevent stress
cracks from forming. Balance is better than 18 gm/cm, and torsional
vibrations are looked after by a modern 3 spoke-style snout dampener, with
most of the weight placed where it will do the most good - at the outer
diameter.
The stroke is 3.405", a shade longer than the 273-340 was at 3.31, but
shorter than the 360's 3.58. Still we'd call it a 'short stroke' engine.
Looking briefly at the block, there is room for some stroke increase.
Having the cam out of the way helps a lot.
Carrying on a performance small-block tradition begun with the 1968 340,
all bearings are bi-metal Federal Mogul aluminum alloy. As in all
production smallblocks, only the upper half of the mains are grooved.
Unlike the previous smallblock, however, thrust isn't taken by a lip on #3
main. Instead, two (front and rear) separate 180-degree thrust
bearing/washers float on the top half of the usual (for Mopar) #3 main
journal.
Connecting rods. Yes ! The long-rod Mopar tradition continues. The 6.12"
length, same as all LA engines have always been, puts rod/stroke ratio at a
very favorable 1.80, better than the current 360, and only a shade worse
than the 273-340.
But the traditional forged steel rod is gone. Now you'll find
powder-forged metal cracked rods. In this process, first used by Chrysler
in the 2.0L SOHC Neon engine, the rods are produced and machined in one
piece. Then the caps are literally cracked off, guillotined if you will,
resulting in an absolutely perfect mating surface that almost lock
together, preventing cap walk. Fasteners are hardened M9 capscrews
threaded directly into the rod, no nuts are used. Rod weight is 556 grams,
compared to 726 to 758 grams for various production LA-engine rods. 0.945"
wrist pins, weighing in at 143 grams, are press-fit in the rods.
Compression ratio is "blueprint" (and advertised) at 9.5:1, and typically
measures 9.0:1. { The Grand Cherokee DC website lists CR as 9.3:1 }
Regular (87) fuel is recommended. But the design allows for
high-compression domed pistons in the future.
Pistons are cast aluminum, have moly coated skirts for break-in scuff
resistance, and weigh 366 grams. They are fitted at 0.0008-0.0020" skirt
clearance - rather snug but nothing unusual for a street engine. The usual
3-groove ring pak is used (.062/.062/.120") but in addition to the common
plasma-moly-filled top rings, the second ring is chrome. Oil rings are
chrome as well, with a stainless expander. Bucking the current trend, the
oil ring tension is rather high (12 lbs) allowing good oil control even in
high-mileage engines. In fact, the spec for the 95th percentile customer
is 150,000 mile useful life.
In the never ending quest to reduce emissions, the distance from the top
ring groove to the top of the piston has been reduced to only 1/8th of an
inch, making these areas susceptable to excess wear and heat. To combat
this, the top ring land, and the area from the land to the head, are hard
anodized.
No oversized pistons are available, and the replacement pistons/rods are
supplied only as an assembly. Can you say aftermarket?
The oiling system isn't radical, using a clever design first seen on the
AMC V8s: the georotor-type pump is mounted in the timing cover, and is
driven off the crank snout. Direct drive, unlike the current LA engine,
which, if you think about it, is a nightmare. The oil pump drive torque
comes off the crank nose, through the chain, to the cam, back through the
full length of the cam, through a bevel gearset to the intermediate shaft,
and then through a hexagonal drive to the pump itself. Whew ! Can you
say, simplified ?
The new, block mounted pump has a 75 psi relief valve, and a displacement
of approx 1 cubic inch per revolution. The oil pan is stamped steel,
includes a windage tray (integral with the pan gasket) and has a capacity
of 5 quarts plus one in the filter. Pump clearances are designed for the
recommended 5W30 oil.
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end of part two
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