2.7L ENGINE COMPONENTS
CYLINDER BLOCK
The cylinder block is made of heat treated alumi-
num with cast-in-place iron liners. The block is a
closed deck design with the right bank forward. To
provide high rigidity and improved NVH, the block
has cast-in contours and ribs, along with powdered
metal 6 bolt main caps (4 vertical, 2 horizontal), with
a die cast aluminum structural beam windage tray
mounted to the main caps.
The block design allows coolant flow between the
cylinder bores and an internal coolant by-pass to a
dual poppet inlet thermostat.
CRANKSHAFT
The crankshaft is constructed of a forged micro
alloy steel. The six throw, nine counterweight crank-
shaft is supported by four select fit main bearings
with the number three serving as the thrust washer
location. The select fit identification markings will be
on the rear side of the number nine (rearmost) coun-
terweight. The six separate connecting rod throws
are an even-firing design which reduces torque fluc-
tuations while a vibration damper is used to control
torsional vibration.
The crankshaft oil seals are a one piece design.
The front seal is retained by the timing chain cover,
and the rear seal in a housing that attaches to the
cylinder block.
PISTONS AND CONNECTING RODS
The pistons are made a high strength aluminum
alloy with an anodized top ring groove and crown.
Piston skirts are coated with a solid lubricant for
scuff resistance. The connecting rods are made of
powdered metal with a “fractured cap” design. The
connecting rod attaches to the piston with a full
floating pin retained by lock rings.
CYLINDER HEADS
The cylinder heads are made of an aluminum alloy.
The cylinder head features four valves per cylinder
with pressed in powdered metal valve guides. The
cylinder heads provide enclosures for the timing
chain drive, necessitating a unique right and left cyl-
inder head.
TIMING DRIVE SYSTEM
The timing drive system has been designed to pro-
vide quiet performance and reliability to support a
NON free-wheeling engine. The system consists of a
primary and secondary chain drive.
The primary timing chain drive uses a single,
double-flexure, inverted tooth type chain. The pri-
mary chain drives both of the intake camshafts
directly from a sprocket mounted on the crankshaft.
In addition, the water pump is driven by the “back
side” of the primary chain, necessitating the double-
flexure type chain.
The chain is controlled by three fixed chain guides
and a pivoting tensioner arm. These guides utilize
low-friction and long wearing nylon plastic wear
faces. To tension the primary chain, a fully automatic
spring-loaded, engine oil-fed, hydraulic tensioner is
used. The tensioner is mounted in the right cylinder
head with the plunger contacting the pivoting ten-
sioner arm. A mechanical ratchet mechanism inside
the tensioner prevents excessive chain slack upon
engine start-up as the chain wears. The tensioner is
designed with an internal oil reservoir to assure
noise-free performance, even during engine start-up
before oil pressure reaches the tensioner.
To reduce engine NVH and timing chain loads a
camshaft damper is used. This damper mounts to the
right intake camshaft sprocket. The damper utilizes
a synthetic rubber elastomer to provide damping,
similar to a crankshaft damper.
For lubrication the primary chain utilizes oil leak-
age from the front of the oil pump. This oil spills on
the crankshaft sprocket, which is then carried by the
chain throughout the primary drive.
The secondary timing chain drive system uses
two conventional roller-type chains, one at each cyl-
inder bank. The purpose of the secondary chain is to
provide a mechanical driven connection between the
intake and exhaust camshafts. The intake camshafts
drive the exhaust camshafts. The sprockets for both
intake and exhaust camshafts are a press-fit and are
only serviced as an assembly with the camshafts.
To tension the secondary chain a spring-loaded,
hydraulic tensioner is used at each bank and
attaches to each cylinder head between the intake
and exhaust camshafts. The tensioner incorporates
upper and lower chain guide faces. The lower guide
face is attached directly to the tensioners hydraulic
plunger. Also, the tensioner uses an internal oil res-
ervoir design to prevent engine start-up noise. The
secondary chains are lubricated via an oil passage
through the upper guide face on each tensioner.
CAMSHAFTS
The assembled fabricated camshafts are composed
of five bearing journals machined into a hollow steel
tube. Six steel lobes, a secondary timing drive
sprocket, and a primary sprocket/thrust flange are
pressed onto the camshaft tube using a unique
assembly process. Camshaft end play is controlled by
the primary camshaft sprocket attachment flange on
the intake camshafts and by a thrust flange on the
exhaust camshafts.
LH
2.7L ENGINE
9 - 19
DESCRIPTION AND OPERATION (Continued)