[Manitcor]

Subject: Cold Engine Tick Noise (Replace Pistons)


Models: 2000-01 Buick Century
2000-01 Chevrolet Lumina, Malibu
2000-01 Pontiac Grand Prix
with 3.1L Engine (VIN J -- RPO LG8


Condition:
Some customers may comment on a ticking noise (similar, but not related to valve or lifter noise) that occurs 10-15 seconds after a cold engine start. The noise will last for 1 to 2 minutes, and will fade as the engine reaches operating temperature.


Cause:
The noise may be caused by excessive piston to bore clearance during cold engine operation resulting from the specific piston design used in cylinders 1 through 4.


Correction:
Service pistons for cylinders 1 through 4 will now be of the same design of those used for all production 2000 and 2001 for cylinders 5 and 6, and will have polymer coated piston skirts. Pistons in cylinders 5 and 6 are not exhibiting the described noise condition.


Important:
Note that this is a customer annoyance issue, and does not affect the durability or life of the engine.


Removal of pistons from engine cylinders 5 and 6 is NOT necessary if equipped with polymer coated pistons. It is recommended to rotate the crankshaft until the piston skirt is exposed in the lower crankcase area for inspection. Replace pistons in engine cylinder positions 5 and 6 ONLY if there is evidence of damage to the polymer coating on the piston skirt, or scoring on the cylinder wall (heavy scratches) is evident. Detailed diagnosis of cylinder wall/piston skirt wear is discussed in step 4 below.


Repair Procedure:
Tools Required
J 24086 Connecting Rod Press
J 24086-C Piston Pin Remover/Installer
Connecting Rod Oven (Rod Kiln)
Piston and Connecting Rod Disassemble


Follow the base engine noise diagnostic information found in the Engine Repair Section of the Service Manual.


Prior to piston/connecting rod removal, mark or identify the piston/connecting rod assembly, and its orientation to the front of the engine, before removal.


Remove the pistons from engine cylinders 1-4 following instructions found in the Engine Repair Section of the Service Manual.


FIGURE Non-Polymer Coated Piston©


Figure 1


(1) Good Piston
(2) Scored Piston


FIGURE Polymer Coated Piston©


Figure 2


(1) Good Piston
(2) Scored Piston


FIGURE Cylinder Wall Finish©


Figure 3


(1) Good Cylinder Wall*
(2) Scored Cylinder Wall*


Important:
*Provided for illustration purposes only. Actual orientation of scuffing on cylinder wall may be different.


Honing of cylinder walls is not recommended for this procedure. If cylinder walls are badly scored, replace the engine assembly.


Reference the above illustrations. Inspect all cylinder walls and piston skirts for scoring. Excessive scoring would be defined by marks which may be felt by a fingernail that is passed over them. Blemishes (discoloration) that appear in the cylinder wall finish, which are not detectable by a fingernail, are not considered cylinder wall/piston skirt defects.


The following engine piston part numbers should be utilized in this repair: Part number 12564009 -- LG8 3.1 Liter Service Piston.


Notice:
A rod kiln MUST be used during assembly of the connecting rod to the piston. If a connecting rod kiln is not available, seek the assistance of a reputable machine shop with a kiln. Under NO circumstances should an acetylene torch or other uncontrolled heating device be used on connecting rods, as permanent damage to the connecting rod may result.


The following steps are provided to assist in the successful replacement of the piston assemblies.


Figure 4


Important:
It is not necessary to replace the piston rings, unless they were damaged during the repair process. If the piston rings are to be reused, mark or identify the location/order of the rings as they correspond to location on the piston being serviced. Refer to ring gap placement instructions found in the Engine Repair Section of the Service Manual.


Using piston ring pliers, remove the piston rings from the piston.


Figure 5


Install the J 24086-310 fork insert into the J 24086-10 fixture support assembly.


Figure 6


Install the piston and connecting rod assembly onto the J 24086-10.


Install the J 24086-107 adapter onto the piston pin, and install the J 24086-88A through the J 24086-10 and onto the J 24086-107.


Figure 7


Important:
The piston and pin are a matched set and are not to be serviced separately.
Press the piston pin from the piston and connecting rod assembly.
Piston and Connecting Rod Assemble


Figure 8


Install the J 24086-310 fork insert into the J 24086-10 fixture support assembly.


Figure 9


Adjust the J 24086-9 installation pin to the following setting: 3.1 liter engine: G-7.


Caution:
Avoid contact with HOT components. Wear safety glasses and protective heat gloves to avoid personal injury!


Notice:
Applying excessive heat to the connecting rod may damage or distort the connecting rod or piston. Connecting rod temperatures should not exceed 320°C (612°F).
Using a connecting rod kiln, heat the piston pin end of the connecting rod to 320°C (612°F).


Figure 10


Refer to the above illustration. Assemble the piston, the connecting rod, and the J 24086-6A adapter as shown. Insert the piston and connecting rod assembly into the J 24086-10 fixture support assembly.


Figure 11


Notice:
After the J 24086-9 installation pin bottoms on the J 24086-10 fixture support assembly, do not exceed a pressure of 35,000 kPa (5,000 psi), or damage to the connecting rod press may result.
Refer to the above illustration. Install the J 24086-105 (2) onto the piston pin. Position the J 24086-9 (1) though the J 24086-10 fixture support assembly and onto the J 24086-105 (2).
Press the J 24086-9 (1) installation pin until it bottoms on the J 24086-10 fixture support assembly.


Reinstall the piston rings onto the new piston. Refer to the Engine Repair Section of the Service Manual for proper ring gap positioning.


Figure 12


Refer to the above illustration. Install the assembled piston and rod assembly into the engine. Verify that the directional arrows on the top of the piston point to the front of the engine.
Follow the remaining engine assembly instructions found in the Engine Mechanical Section of the Service Manual.


Parts Information:
Part Number Description Qty
12564009 LG8 3.1 Piston Assembly 4


Parts are currently available from GMSPO.


GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.


© Copyright General Motors Corporation. All Rights Reserved.