Service Bulletin

Bulletin No.:

23-NA-115

Date:

July, 2023

TECHNICAL
Subject:

Ticking, Tapping or Snapping Noise from Engine - 5.5L RPO LT6 Realign Camshaft
Caps as Required
This bulletin replaces PIP5920. Please discard PIP5920.

Brand:

Model:

Chevrolet

Corvette

Model Year:

VIN:

from

to

from

to

2023

2023

—

—

Engine:

Transmission:

5.5L
(RPO LT6)

—

Involved Region or Country

North America

Condition

Some customers may comment on a ticking, tapping, or snapping noise from the engine.
Note: It is important to note that this engine incorporates a mechanical valve train design
to enable maximum engine performance and does not use traditional hydraulic lifters and
as a result there will be some mechanical tick noise from the valvetrain, which is normal.
However, if the noise is excessive and not periodic, as described in this bulletin, this
procedure can be used to reduce the noise. For reference, this ticking disturbance noise
can be heard while the engine is idling and more noticeable with the hatch open and in
tour mode. It may also be found that the noise slightly increases as the engine gets
towards operating temperature.

Cause

This condition may be caused by the misalignment of the camshaft caps.
The verify you have this concern, it will be necessary to follow the steps below. Do not
proceed with this bulletin if the customer has not commented about this concern.
Important: Please read entire bulletin prior to performing any repair.

Correction

Copyright 2023 General Motors LLC. All Rights Reserved.

Important: You MUST use the PicoScope to verify if you have this noise concern.
Failure to use the PicoScope may result in incorrect diagnosis and the need for further or
unnecessary repairs.
Important: You need to take PicoScope measurements before and after the repair to
share with customer. Before performing any repair on the left or right side of the engine
please review the realignment procedure with the customer and ask them if they want to
proceed with the repair.
Important: Not all engines will see the same level of noise reduction after performing the
realignment procedure. Some engines may see a marginal improvement in noise
reduction.

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Bulletin No.: 23-NA-115

Important: Service agents must comply with all
International, Federal, State, Provincial, and/or
Local laws applicable to the activities it performs
under this bulletin, including but not limited to
handling, deploying, preparing, classifying,
packaging, marking, labeling, and shipping
dangerous goods. In the event of a conflict between
the procedures set forth in this bulletin and the
laws that apply to your dealership, you must follow
those applicable laws.

Service Procedure
Step 1:
Follow the directions below to setup the PicoScope to
obtain the sound file needed for review.
If you need to download or update the PicoScope,
follow the steps below:
1. Log into GM GlobalConnect.
2. Click on the "Departments" drop down menu and
select "Service.”
3. Under "Applications" on the service page, select
"Special Tools and Software updates.” (in Canada,
"GM Special Tools & Equipment - Software
Updates")
4. You will now be re-directed to
www.gmtoolsandequipment.com (do not access
this site directly as it requires the use of
GlobalConnect to allow downloads).
5. Click the link under "Software Downloads" for the
latest PicoScope software version and a new page
will open.

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6. Click the setup links and follow instructions to
update the tool.

Step 2:
⇒ Start up the vehicle/engine. Ensure engine is at
operating temperature. Stand on the driver's side
and then passenger side of the engine to listen to
the suspected tick. Subjectively determine which
bank (LH vs RH) has a more prominent tick and
proceed with instrumenting on that bank.
Determine which side of the engine the noise is
coming from.

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Step 3:
Place the accelerometer on the suspect bank.

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⇒ With the suspect bank determined, prep/position
the accelerometer so the X, Y, Z coordinate system
(that’s laser etched) is facing upwards before
securing to the bolt head. After accelerometer is
placed on bolt head, double check to ensure its
centered and did not rotate on the bolt head. Doing
so will ensure the best results.

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Bulletin No.: 23-NA-115

Note: Ensure to keep the cable routed away from the
exhaust if working in the engine compartment or
moving parts if working under the vehicle.

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Important: Ensure accelerometer coordinates are
facing up towards the intake.

Step 4:
Hook up the accelerometer to the oscilloscope.
⇒ Screw the accelerometer connector into the sensor
interface. The red LED will start to blink when it
senses the connection. Attach a blue, red, and
green BNC cable to X, Y, and Z ports, respectively.
Then attach the blue, red, and green cables to
channels A, B, and C, respectively.

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July, 2023

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Step 5:
Setup the software to collect data.
1. Open the GM NVH software and click on the NVH
button.

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2. Start a new test with the setup wizard:
⇒ 1) Under RPM Signal – Ensure Static RPM is
set to 800 RPM.
⇒ 2) Under Vibration Signal – Select three-axis
mode then ensure all 3 channels are checked
and the location is set to Engine Compartment.
⇒ 3) Under Signal Options – Set the Maximum
Signal History Size to 500 seconds.
3. Go to the setup screen to finalize the wizard setup.

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Bulletin No.: 23-NA-115

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4. Go to options at the top then to advanced options
and change the maximum frequency of interest to
2000. Update the SPL Weighting to dB(A) and
check that the accelerometer units are (m/s^2).
Under the FFT tab, change the responsiveness
marker to the position shown above. Finally, under
the filter tab, add a bandpass filter from 1300 to
2000 Hz.

Note: If the instrumentation needs to be moved, restart
the data collection.
4. After finishing the recording, click file then save.
Click OK on the details box as this input is optional
and save as a .pddata. Change the file name to
“[last 8 of vin]_[LH or RH bank]_[pre or post service
fix]_[date].”

Step 6:

Step 7:

Collect data.
1. Startup the vehicle/engine, leave at idle. Make
sure the HVAC is off and the vehicle is put into
weather mode so that the vehicle idles at 800 rpm.
Let the engine settle and wait for the suspected
tick to start.
2. When the suspected tick starts, click on the “start
recording” button. Let the recording go for 60
seconds, then click “stop recording.” Do not adjust
the accelerometer throughout the recording.

Analyze the data.
1. Right click in the time domain display and change
the display mode to single.
2. If scales on the left end for each channel are not
ranging from -4 m/s^2 to 4 m/s^2, right click in the
time domain display and select “reset scale.”
3. Pull the yellow window cursors on the bottom in as
close together as they will go.
4. Look at the channel lines in the time domain
window for ticks with a .15s gap between them.
⇒ Compare to the examples below for an engine
with a tick and an engine without a tick:

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Examples of Tick:

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Examples of No Tick:

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Important: Once you have captured your Pico results
before and after performing the service procedure,
please reset the settings menu to default for the next
user by clicking on the reset buttons at the bottom of
the advance PICO set up screens.
Once it is determined which bank the noise is coming
from, it will be necessary to follow the service
procedure below to adjust the camshaft cap torque.
Important: If the noise is heard from the left bank, the
camshaft cap adjustment procedure can be done with
powertrain in vehicle. If the noise is heard coming from
the right bank, it will be necessary to drop the engine
and transmission assembly to gain access and remove
the camshaft cover for the adjustment procedure.
Important: Please review the PICO results with the
customer and give them the option if they want their
powertrain removed and reinstalled for repair on the
passenger side.
Important: Ensure you batteries in the interface
module are good.

Camshaft Cap Re-Alignment Procedure:
Please use the following procedure to execute a
complete bank camshaft re-alignment procedure:
1. If the tick noise is on the Driver’s side bank 1, the
repair can be done in the vehicle. If the tick is on
the passenger side bank 2, the rear cradle and
powertrain assembly must be lowered to be able to
remove the camshaft cover on that bank.
– Refer to Camshaft Cover Replacement – Bank 1
or Camshaft Cover Replacement – Bank 2 in SI