Engine - Knocking/Thumping Noise

91lexus04

ENGINE

006

SEPTEMBER 13, 1991

VV


Title ENGINE KNOCKING/THUMPING NOISE ON ES250


To diagnose and repair engine thumping noise between 1100 rpm and 1200 rpm, the following procedure should be followed:


DIAGNOSIS

Engine thumping noise may be confirmed under the following conditions:

1. Engine temperature: HOT.
2. Air conditioning: COMPRESSOR ON, TEMPERATURE SET AT FULL COLD.
3. Blower motor: LOW.
4. Radio: OFF.
7. Transmission: DRIVE (for automatic), or 1st (for manual).
8. Road: SLIGHT UPWARD INCLINE, SUCH AS A LONG DRIVEWAY.
9. Thumping noise may be heard while vehicle creeps forward at less than 5 mph and engine speed is between 1100 and 1200 rpm. This thumping noise is often accompanied by excessive floorboard vibrations.


REPAIR PROCEDURE

STEP 1. Reduce A/C drive belt tension to 95 lbs.


2. Test drive vehicle and confirm effectiveness.

3. If NOT effective, continue with STEPs (4) and (5).

4. Measure crankshaft # 1 Main Journal Bearing oil clearance.

5. Decrease # 1 Main Journal Bearing oil clearance by installing a thicker Main Journal Bearing which is 1 or 2 "mark" sizes larger than the original bearing.

Example: Original mark 3 main journal bearing would be replaced by either a mark 4 or mark 5 bearing.

CAUTION: The oil clearance must not be less than 0.001 in.

NOTE: Refer to Repair Manual RM240U, pages EM-75 and 76 for method of determining
Main Journal Bearing oil clearance.


PARTS INFORMATION:

Two new Main Journal Bearings sizes (Mark "6" and "7") are available for replacement in vehicles originally fitted with Mark "4" or "5" Main Journal Bearing.


NEW PART NAME NEW PART NO. BEARING CENTER WALL
THICKNESS


Bearing Set, Crankshaft 11701-62020-06 0.0789 - 0.0790 in.
(Mark "6") (2.004 - 2.007 mm)

Bearing Set, Crankshaft 11701-62020-07 0.0790 - 0.0791 in.
(Mark "7") (2.007 - 2.010 mm)