Lexus SC300 / Lexus SC400. Service manual — part 721

DESCRIPTION

The 1 UZ–FE engine is an V–8 4.0 liter DOHC 32 valve engine.

OPERATION

EM–2

–

ENGINE MECHANICAL

Description, Operation

DESCRIPTION

The 1 UZ–FE engine is an V–8 4.0 liter DOHC 32 valve engine.

OPERATION

EM–2

–

ENGINE MECHANICAL

Description, Operation

–

ENGINE MECHANICAL

Operation

EM–3

The 1 UZ–FE engine has 8–cylinders in a V–arrangement at a bank angle of 90

°

. From the front of the RH

bank cylinders are numbered 2–4–6–8, and from the front of the LH bank cylinders are numbered 1 –3–5–7.
The crankshaft is supported by 5 bearings specified by the inside of the crankcase. These bearings are made
of a copper and lead alloy.

The crankshaft is integrated with 8 weights which are cast along with it for balancing. Oil holes are built

into the center of the crankshaft for supplying oil to the connecting rods, pistons and other components.

The ignition order is 1–8–4–3–6–5–7–2. The cylinder head is made of aluminum alloy, with a cross flow

type intake and exhaust layout and with pent–roof type combustion chambers. The spark plugs are located in
the center of the combustion chambers.

At the front and rear of the intake manifold, a water passage has been provided which connects the RH

and LH cylinder heads.

Exhaust and intake valves are equipped with irregular pitch springs made of special valve spring carbon

steel which are capable of following no matter what the engine speed.

The RH and LH intake camshafts are driven by a single timing belt, and a gear on the intake camshaft en-

gages with a gear on the exhaust camshaft to drive it. The camshaft journal is supported at 5 (intake) or 4 (ex-
haust) places between the valve lifters of each cylinder and on the front end of the cylinder head. Lubrication
of the cam journal gear is accomplished by oil being supplied through the oiler port in the center of the camshaft.

Adjustment of the valve clearance is done by means of an outer shim type system, in which valve adjusting

shims are located above the valve lifters. This permits replacement of the shims without removal of the cam-
shafts.

Pistons are made of high temperature–resistant aluminum alloy, and a depression is built into the piston

head to prevent interference with valves.

Piston pins are the full–floating type, with the pins fastened to neither the piston boss nor the connecting

rods. Instead, snap rings are fitted on both ends of the pins, preventing the pins from falling out.

The No.1 compression ring is made of steel and the No.2 compression ring is made of cast iron. The oil

ring is made of a combination of steel and stainless steel. The outer diameter of each piston ring is slightly larger
than the diameter of the piston and the flexibility of the rings allows them to hug the cylinder walls when they
are mounted on the piston. Compression rings No.1 and No.2 work to prevent the leakage of gas from the cylin-
der and the oil ring works to scrape oil off the cylinder walls to prevent it from entering the combustion chamber.

The cylinder block is made of aluminum alloy with a bank angle of 90

°

. Cast iron cylinders are installed

inside the cylinder block. It has 8 cylinders which are approximately twice the length of the piston stroke. The
top of each cylinder is closed off by the cylinder heads and the lower end of the cylinders becomes the crank-
case, in which the crankshaft is installed. In addition, the cylinder block contains a water jacket, through which
coolant is pumped to cool the cylinders.

The No.1 and No.2 oil pans are bolted onto the bottom of the cylinder block. The No.1 oil pan is made of

aluminum alloy. The No.2 oil pan is an oil reservoir made of pressed steel sheet. An oil level sensor is installed
in the No.1 oil pan (If the oil level drops below a set level, a warning light lights up.). A oil pan baffle plate keeps
sufficient oil in the bottom of the No.2 oil pan even when the vehicle is tilted. This dividing plate also prevents
the oil from making waves when the vehicle is stopped suddenly and the oil shifts away from the oil pump suction
pipe.

Plastic region tightening bolts are used for the cylinder head, main bearing cap and connecting rod.

EM–4

–

ENGINE MECHANICAL

Operation