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Autopapyrus · Mercedes-Benz Actros 2013 12.8 (OM471)
https://autopapyrus.com/guides/mercedes-benz/actros/valve-clearance-adjustment/
Compiled automatically from service literature and owner experience. Specs are for the typical configuration — check them against your exact car before you start.

Mercedes-Benz Actros 2013 12.8 (OM471): Valve Clearance Adjustment

"Valves" are the parts being adjusted here. On the OM471 inline-six, the valves are actuated through rocker arms with adjusting screws, and the engine brake (decompression brake, EPB) acts on the exhaust valves. Clearances are checked according to the maintenance schedule, when valve train noise appears, or after work on the cylinder head. The adjustment is done on a fully cooled engine, following the cylinder sequence. The exact clearance values and locknut torques are given in the manufacturer's service manual: check them before starting. The general procedure is below.

Difficulty: Hard Time: 3-5 hours Steps: 11 Tools: torque wrench (low range, 5-60 N·m (4-44 lb-ft)), feeler gauge set, crankshaft turning tool (barring device or socket for the pulley nut), sockets and wrenches for the rocker arm adjusting screws, ratchet wrench, clean rags, engine oil for lubricating threads, new cylinder head cover gaskets

Part

  • 🔩 cylinder head cover gasket set (one gasket per engine cover section), spark plug/injector sealing rings if needed

Step by step

11 steps
  1. Let the engine cool to ambient temperature (at least several hours). Park the vehicle on level ground, with the parking brake applied and the transmission in neutral, and chock the wheels. Disconnect the battery ground cable.
  2. Tilt the cab. Clean the area around the valve covers so that dirt cannot get inside. Remove the air and ventilation hoses that block access, and disconnect the wiring harnesses on the covers, noting their markings.
  3. Remove the cylinder head covers carefully, without tilting them and without prying with a screwdriver on the mating surface. Replace the old gaskets.
  4. Prepare to turn the crankshaft: use the barring device on the flywheel housing or a wrench on the nut at the front end of the crankshaft. Turn it only in the direction of engine rotation. Remember the firing order: 1-5-3-6-2-4.
  5. Set the crankshaft to TDC of cylinder 1 on the compression stroke (the mark on the pulley/flywheel aligns with the pointer; the valves of cylinder 1 are closed, and cylinder 6 is in valve overlap). In this position, check and, if necessary, adjust the valve clearances of the cylinders specified in the service manual for this position.
  6. Checking: insert a feeler gauge of the required thickness between the rocker arm and the valve bridge/stem. The gauge should slide with slight resistance. Intake and exhaust clearances differ: the exhaust clearance is larger. Take the exact values for the OM471 from the manufacturer's service manual, and do not rely on figures for other Mercedes engines.
  7. Adjustment: loosen the locknut of the adjusting screw, set the clearance with the screw while the feeler gauge is inserted, holding the screw with a screwdriver, tighten the locknut to the specified torque (per the service manual, usually in the range of 25-45 N·m (18-33 lb-ft), confirm the exact value), and recheck the clearance with the feeler gauge after tightening.
  8. Turn the crankshaft 360° (or the angle specified in the service manual) and repeat the procedure for the second group of cylinders. Be sure to follow the sequence so that you do not skip a cylinder.
  9. Do not change the factory settings on the engine brake (EPB) mechanisms unless the service manual instructs you to. If the brake rocker arm clearance is out of tolerance, adjust that assembly as a separate procedure.
  10. Install new gaskets and tighten the cover bolts evenly, from the center outward, to the torque specified in the service manual. Reconnect the harnesses and hoses, tilt the cab back down, and reconnect the battery.
  11. Start the engine, warm it up, and check for oil leaks from under the covers, smooth running, and absence of knocking. If necessary, read fault codes with a diagnostic scan tool.

Common mistakes and warnings

  • Incorrect clearance leads to burned valves or loss of compression, and a mistake when working on the engine brake components can destroy the engine. If you have no experience with heavy-duty diesels, leave the adjustment to a repair shop. Work only on a cold engine, and lock the engine against turning when working under the cab.