How to Adjust the Valves and Injectors on a Detroit Series 60 12.7L Engine

The Detroit Series 60 12.7L engine is a popular diesel engine that powers many heavy-duty vehicles and equipment. It has a single overhead camshaft that operates two intake and two exhaust valves per cylinder, as well as the fuel injectors. To ensure optimal engine performance and fuel efficiency, it is important to adjust the valve lash and injector height at regular intervals. In this article, we will explain the basic steps and tools required to perform this maintenance task.

What is Valve Lash and Injector Height?

Valve lash is the clearance between the valve stem and the valve button at the end of the rocker arm. This clearance affects the timing and duration of the valve opening and closing, which in turn affects the engine’s power, torque, and emissions. If the valve lash is too tight, the valves may not close completely, resulting in loss of compression and increased wear. If the valve lash is too loose, the valves may open too late or too early, resulting in poor combustion and reduced performance.

Injector height is the distance between the injector body and the injector follower, which is connected to the rocker arm. This distance affects the timing and amount of fuel injected into the cylinder, which also affects the engine’s power, torque, and emissions. If the injector height is too high, the fuel injection will be delayed, resulting in lean mixture and reduced power. If the injector height is too low, the fuel injection will be advanced, resulting in rich mixture and increased emissions.

When and How to Adjust the Valve Lash and Injector Height?

According to the manufacturer’s recommendation, the valve lash and injector height on the Detroit Series 60 12.7L engine should be measured and adjusted at the initial period of 96,000 km (60,000 miles) or 24 months, whichever comes first. After that, any adjustments should be made only as needed to maintain satisfactory engine performance.

To adjust the valve lash and injector height, you will need the following tools and equipment:

  • A clean, dry, and well-lit work area
  • A torque wrench
  • A feeler gauge
  • An injector height gauge
  • A wrench or socket set
  • A screwdriver
  • A clean rag
  • Safety glasses and gloves

The adjustment procedure is as follows:

  1. Park the vehicle on a level surface and apply the parking brake. Turn off the engine and disconnect the battery cables. Wait for the engine to cool down completely before proceeding.
  2. Remove the valve cover and gasket from the cylinder head. Inspect the gasket for damage and replace it if necessary. Clean the valve cover and the cylinder head surface with a rag.
  3. Rotate the engine by hand using a barring tool until the No. 1 piston is at top dead center (TDC) on the compression stroke. You can verify this by aligning the timing marks on the crankshaft pulley and the gear case cover, and by checking that both the intake and exhaust valves on the No. 1 cylinder are closed.
  4. Refer to the table below to determine which valves and injectors need to be adjusted when the No. 1 piston is at TDC. The table shows the cylinder number and the valve/injector designation. For example, 1I means the intake valve on the No. 1 cylinder, and 5E means the exhaust valve on the No. 5 cylinder.
Cylinder Valve/Injector
1 I, E, INJ
5 I, E
3 I, E
6 I, E, INJ
  1. To adjust the intake valves, insert a 0.203 mm (0.008 in.) feeler gauge between the tip of the valve stem and the valve button at the end of the rocker arm. Loosen the locknut, and turn the adjusting set screw until the feeler gauge produces an even smooth pull between the valve stem and valve button. Torque the locknut to 41-47 N·m (30-35 lb·ft), and remove the feeler gauge. Insert the feeler gauge again to ensure that the adjustment did not change when the locknut was tightened. Readjust as necessary.
  2. To adjust the exhaust valves, insert a 0.508 mm (0.020 in.) feeler gauge between the tip of the valve stem and the valve button at the end of the rocker arm. Follow the same steps as for the intake valves.
  3. To adjust the injector height, use the injector height gauge that matches the engine model and application. For example, for a DDEC IV engine, use J-42749. Place the gauge on the injector body, with the tip in the locating hole and the handle in the 90-degree position. Loosen the locknut, and turn the adjusting screw until the gauge handle is parallel to the injector follower. Torque the locknut to 41-47 N·m (30-35 lb·ft), and remove the gauge. Check the adjustment again with the gauge and readjust as necessary.
  4. Rotate the engine by hand until the No. 6 piston is at TDC on the compression stroke. You can verify this by aligning the timing marks on the crankshaft pulley and the gear case cover, and by checking that both the intake and exhaust valves on the No. 6 cylinder are closed.
  5. Refer to the table below to determine which valves and injectors need to be adjusted when the No. 6 piston is at TDC.
Cylinder Valve/Injector
6 I, E
2 I, E, INJ
4 I, E, INJ
1 I, E
  1. Follow the same steps as before to adjust the valves and injectors on the corresponding cylinders.
  2. After all the adjustments are done, reinstall the valve cover and gasket on the cylinder head. Torque the valve cover bolts to 24-30 N·m (18-22 lb·ft) in a crisscross pattern. Reconnect the battery cables and start the engine. Check for any leaks, noises, or performance issues. If any problems are found, repeat the adjustment procedure or consult a qualified technician.

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