Lexus RX300 (MCU15). Service manual — part 39

EG

ENGINE — 1MZ-FE ENGINE

Engine
Front

Cast Iron

Torsional
Damper
Rubber

Steel

Aluminum

187EG14

29

7. Crankshaft

D The crankshaft is made of forged steel and has 4 journals and 9 balance weights.

D All pins and journals fillets are roll-finished to maintain adequate strength.

D The crankshaft bearings for the No. 1 and No. 4 journals are made wider to decrease noise and vibration,

and those for the No. 2 and No. 3 journals are made narrower to reduce friction.

Roll-Finished

Engine
Front

Balance Weight

Oil Hole

No. 1 Journal

No. 4 Journal

187EG13

8. Crankshaft Pulley

D The crankshaft pulley hub is made of aluminum

to reduce weight and vibration.

D The rigidity of the torsional damper rubber has

been optimized to reduce noise.

ENGINE — 1MZ-FE ENGINE

Intake Camshaft

VVT-i Controllers

Exhaust Camshaft

157EG22

30

JVALVE MECHANISM

1. General

D Each cylinder has 2 intake valves and 2 exhaust valves.

D The valves are directly opened and closed by 4 camshafts.

D The exhaust camshafts are driven by a timing belt, while the intake camshafts are driven through gears

on the exhaust camshafts.

D The VVT-i system is used to improve fuel economy, engine performance and reduce exhaust emission.

For details, see page 48 (VVT-i System Section).

2. Camshafts

D In conjunction with the adoption of the VVT-i system, an oil passage is provided in the intake camshaft

in order to supply engine oil to the VVT-i system.

D A VVT-i controller has been installed on the back of the intake camshaft to vary the timing of the intake

valves.

D To detect the camshaft position, a timing rotor that is provided on the VVT-i controller is used to generate

3 pulses for every 2 revolutions of the crankshaft.

D The intake camshafts are driven by gears on the exhaust camshafts. The scissors gear mechanism is

used on the exhaust camshaft to control backlash and suppress gear noise.

No. 2 Camshaft (Exhaust)

No. 1 Camshaft (Intake)

No. 3 Camshaft (Intake)

No. 4 Camshaft (Exhaust)

Scissors Gear Mechanism

VVT-i Controllers

Timing Rotor

Scissors Gear Mechanism

187EG15

EG

ENGINE — 1MZ-FE ENGINE

187EG16

187EG17

Camshaft

Adjusting Shim

Valve Lifter

Valve

Adjusting Shim

Valve Lifter

Cutout

Camshaft Timing Pulleys

No. 2 Idler

No. 1 Idler
(Tension
Adjuster)

Timing Belt Tensioner

Crankshaft Timing Pulley

Water Pump
Pulley

187EG18

31

3. Intake and Exhaust Valve and Valve Lifter

D Narrower valve stems have been adopted to reduce the intake and exhaust resistance and for weight

reduction.

D The adjusting shim has been located directly above the valve lifter. This construction allows the adjusting

shim to be replaced without removing the camshaft, which improves the serviceability during valve clear-
ance adjustment.

D A cutout is provided in the valve lifter to improve the serviceability of replacing the adjusting shims.

" Specifications A

mm (in.)

Item

Intake Valve

Exhaust Valve

Face
Diameter

34.0 (1.34)

27.3 (1.07)

Stem Diameter

5.5 (0.22)

5.5 (0.22)

4. Timing Belt

The timing belt tooth configuration has been de-
signed to help to reduce noise and to enable the belt
to transmit power under high load factors.

ENGINE — 1MZ-FE ENGINE

Tension
Spring

Compression
Spring

187EG19

Belt
Tensioner
Rod

32

5. Timing Belt Tensioner

The timing belt tensioner uses a spring and siricon
oil damper, and maintains proper timing belt tension
at all times.
The timing belt tensioner suppresses noise generated
by the timing belt.

6. Timing Belt Cover

The timing belt cover is divided into 3 pieces, designated No. 1 to No. 3. The NO. 1 and 2 timing belt
covers are made of resin, and tightened with evenly spaced bolts. The No. 3 timing belt cover is made
of steel sheet, and is attached to the engine via rubber bushings to reduce noise.

No. 2 Timing Belt Cover

No. 3 Timing Belt Cover

No. 1 Timing Belt Cover

Spaced Bolt

187EG20