PISTON AND CONNECTING ROD
DESCRIPTION
CAUTION: Do not use a metal stamp to mark con-
necting rods as damage may result, instead use ink
or a scratch awl.
EARLY BUILD
The pistons are made of a high strength aluminum
alloy with an anodized top ring groove and crown.
Piston skirts are coated with a solid lubricant
(Molykote) to reduce friction and provide scuff resis-
tance. The connecting rods are made of forged pow-
dered metal, with a “fractured cap” design. A pressed
fit piston pin is used to attach the piston and con-
necting rod.
LATE BUILD
The pistons are made of high strength aluminum
alloy. The top ring groove and crown are Not anod-
ized, instead the top ring is coated with an anti-scuff
coating to reduce friction on the top ring. The piston
skirts are coated with a solid lubricant (Molykote) to
reduce friction and provide scuff resistance. The con-
necting rods are made of forged powdered metal,
with a “fractured cap” design. A pressed fit piston pin
is used to attach the piston and connecting rod.
CYLINDER HEAD
DESCRIPTION
The cylinder heads are made of an aluminum alloy.
The cylinder head features two valves per cylinder
with pressed in powdered metal valve guides. The
cylinder heads also provide enclosures for the timing
chain drain, necessitating unique left and right cylin-
der heads.
VALVE GUIDES
DESCRIPTION
The valve guides are made of powered metal and
are pressed into the cylinder head. The guides are
not replaceable or serviceable, and valve guide ream-
ing is not recommended. If the guides are worn
beyond acceptable limits, replace the cylinder heads.
VALVES
DESCRIPTION
The valves are made of heat resistant steel and
have chrome plated stems to prevent scuffing. Each
valve is actuated by a roller rocker arm which pivots
on a stationary lash adjuster. All valves use three
bead lock keepers to retain the springs and promote
valve rotation.
VALVE STEM SEAL
DESCRIPTION
The valve stem seals are made of rubber and incor-
porate an integral steel valve spring seat. The inte-
gral garter spring maintains consistent lubrication
control to the valve stems.
VALVE SPRING
DESCRIPTION
The valve springs are made from high strength
chrome silicon steel. The springs are common for
intake and exhaust applications. The valve spring
seat is integral with the valve stem seal, which is a
positive type seal to control lubrication.
HYDRAULIC LASH ADJUSTER
DESCRIPTION
Valve lash is controlled by hydraulic lash adjusters
that are stationary mounted in the cylinder heads.
The lash adjusters have a hole in the ball plunger
that feeds oil through the rocker arm squirt holes for
rocker arm roller and camshaft lobe lubrication.
TIMING DRIVE SYSTEM
DESCRIPTION
The timing drive system has been designed to pro-
vide quiet performance and reliability to support a
non-free wheeling engine. Specifically the intake
valves are non-free wheeling and can be easily dam-
aged with forceful engine rotation if camshaft-to-
crankshaft timing is incorrect. The timing drive
system consists of a primary chain and two second-
ary timing chain drives.
OPERATION
The primary timing chain is a single inverted tooth
type. The primary chain drives the large fifty tooth
idler sprocket directly from a 25 tooth crankshaft
sprocket. Primary chain motion is controlled by a
pivoting leaf spring tensioner arm and a fixed guide.
The arm and the guide both use nylon plastic wear
faces for low friction and long wear. The primary
chain receives oil splash lubrication from the second-
ary chain drive and oil pump leakage. The idler
sprocket assembly connects the primary and second-
ary chain drives. The idler sprocket assembly con-
sists of two integral thirty tooth sprockets and a fifty
tooth sprocket that is splined to the assembly. The
spline joint is a non – serviceable press fit anti rattle
type. A spiral ring is installed on the outboard side of
the fifty tooth sprocket to prevent spline disengage-
ment. The idler sprocket assembly spins on a station-
ary idler shaft. The idler shaft is press-fit into the
cylinder block. A large washer on the idler shaft bolt
and the rear flange of the idler shaft are used to con-
trol sprocket thrust movement. Pressurized oil is
routed through the center of the idler shaft to pro-
vide lubrication for the two bushings used in the
idler sprocket assembly.
9 - 66
4.7L ENGINE
WJ
DESCRIPTION AND OPERATION (Continued)
2000 WJ Service Manual
Publication No. 81-370-0047
TSB 26-12-99
December, 1999