No.: 21TS-06
April 2021
TO:

Service Locations

FROM:

Service Systems Engineering

SUBJECT:

Gen 5 DD15 Exhaust Valve Adjusting Screw Excessive Wear

ISSUE
Some Detroit Heavy Duty Gen 5 DD15 engines are experiencing exhaust valve bridges that fall
out of position while running. The engine may experience conditions such as rough running,
misfire, or popping out of the intake. Misfire or exhaust pressure fault codes may also be
present.

Figure 1. Exhaust Valve Bridge Out of Position
CAUSE
Excessive valve lash caused by a worn rocker arm adjusting screw foot results in the valve
bridge falling off the exhaust valves.

Detroit Diesel 13400 Outer Drive, West / Detroit, Michigan 48239-4001

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4/15/2021

REQUIRED ACTION
Replace the affected valve bridge and inspect the related valve train components on that
cylinder for wear or damage. Do not replace the exhaust camshaft unless there is damage to
the camshaft lobes. Remove and measure the length of all six exhaust rocker arm adjusting
screws to determine amount of wear. The adjusting screw length specification is between 42.45
and 43.85 mm (1.67 and 1.73 in).
REPAIR PROCEDURE
1. Turn ignition OFF, apply parking brake, chock wheels, and perform any other applicable
safety steps.
2. Steam clean the engine.

ELECTRICAL SHOCK
To avoid injury from electrical shock, use care when connecting battery cables.
The magnetic switch studs are at battery voltage.
3. Disconnect the batteries.
4. Open the hood.
5. If necessary, remove bumper for access.
6. Remove air filter housing.
7. If equipped, remove air compressor resonator.
8. Remove the rocker cover.
9. Position the engine at Top Dead Center (TDC) on the appropriate cylinder.
10. Loosen and remove the exhaust rocker arm adjusting screw locknut.
11. Thread the adjusting screw down between the exhaust valves to remove the screw from the
exhaust rocker arm.
12. Measure the length of the adjusting screw. Replace the adjusting screw if the length does
not meet the specification between 42.45 and 43.85 mm (1.67 and 1.73 in). See below
example.

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Figure 2. Measuring Rocker Arm Adjusting Screw
13. Install rocker arm adjusting screw by threading it up from the bottom of the rocker arm tip.
14. Loosely install the rocker arm adjusting screw locknut.
15. Install exhaust valve bridge onto the exhaust valves. Make sure the bridge fully seats on the
front exhaust valve and rear exhaust valve cap.

Note: A new exhaust valve bridge must be installed only when it is found out of position. Reuse
the exhaust valve bridge if it is properly positioned and the adjusting screw was removed for
measurement.

16. Adjust the valve and engine brake lash for all cylinders. REFERENCE the chapter “Engine
Mechanical” and section “Setting the Valve and Engine Brake Lash” in the Gen 5 DD15
Platform Workshop Manual (DDC-SVC-MAN-0215). Note: the torque for the engine brake
adjusting screw locknut is 30 N·m (22 lb·ft). This is much lower than GHG17 heavy-duty
engines.
17. Install the rocker cover. REFERENCE the chapter “Engine Mechanical” and section
“Installation of the Rocker Cover” in the Gen 5 DD15 Platform Workshop Manual (DDCSVC-MAN-0215).
18. If equipped, install air compressor resonator.
19. Install air filter housing.

ELECTRICAL SHOCK
To avoid injury from electrical shock, use care when connecting battery cables.
The magnetic switch studs are at battery voltage.
20. Connect batteries.

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21. Start engine (key ON, engine ON) and check for oil leaks.
22. If removed, install bumper.
23. Close the hood.
CLAIM PROCESS
Normal in-warranty procedures apply. PFP: Exhaust rocker arm adjusting screw

CONTACT INFORMATION
Please contact the Detroit Diesel Customer Support Center at 800-445-1980 or email
[email protected] if you have any questions.

4/15/2021