Valve Spring - Single

Replacement of a single valve spring on the M275 6.0L BiTurbo V12 engine, requiring removal of valve cover, camshaft positioning, and valve spring compression to access the affected spring.

Warnings

Tools required

Parts

• Valve spring (single) × 1 — Use OEM specification for M275 engine
• Valve cover gasket set (affected bank) × 1 — Use OEM specification
• Spark plug tube seals × 1 — Use OEM specification
• Valve stem seal (if damaged during removal) × 1 — Use OEM specification
• Anti-seize compound × 1 — High-temperature nickel-based

Fluids

• Mercedes-Benz 229.5 5W-40 — 1 qt

Preparation

1. Disconnect negative battery terminal and wait 10 minutes for system capacitor discharge
2. Ensure engine is completely cold to prevent warping of aluminum cylinder heads
3. Remove engine cover panels and air intake components to access the affected valve cover
4. Photograph or mark all electrical connectors and vacuum lines for proper reinstallation
5. Remove ignition coils from affected bank and store in order
6. Identify and document the exact cylinder and valve requiring spring replacement

Procedure

1. 1

   Remove spark plugs from affected bank
   Remove all spark plugs from the cylinder bank requiring service. Inspect plug threads and apply anti-seize compound to threads before setting aside for reinstallation. This allows camshaft rotation and prevents cross-threading during reassembly.
   Torque spec

   Spark Plugs - Aluminum Head20 Nm (15 lb-ft)
2. 2

   Remove valve cover
   Disconnect all electrical connectors, breather hoses, and vacuum lines from valve cover. Remove valve cover bolts in reverse of tightening sequence (outside to inside pattern). Carefully lift valve cover off, ensuring gasket material doesn't fall into engine. Clean gasket surfaces thoroughly with plastic scraper.
   ⚠Do not pry against aluminum head surface. If cover is stuck, gently tap with rubber mallet at designated lift points only.
   Torque spec

   Cover Bolts22 Nm (16 lb-ft)
3. 3

   Rotate engine to position target cylinder camshaft
   Manually rotate crankshaft using 27mm socket on crankshaft bolt (clockwise only) until the cam lobe for the affected valve is pointing directly away from the valve (base circle position). This relieves tension on the rocker arm. Verify piston is not at TDC to prevent valve-to-piston contact.
   ⚠️Never rotate engine counterclockwise on M275. The variable valve timing system can be damaged by reverse rotation.
4. 4

   Remove rocker arm
   With cam lobe pointing away from valve, remove the rocker arm mounting bolt for the affected valve. Carefully lift rocker arm straight up and store in labeled container. Inspect rocker arm pad and camshaft lobe for unusual wear patterns.
   ℹ️M275 rocker arms have hydraulic lash adjusters that may drain during removal. Keep rocker arm upright to minimize oil loss.
   Torque spec

   Rocker Arm Bolts30 Nm (22 lb-ft)
5. 5

   Apply compressed air to hold valve closed
   Thread compressed air adapter into spark plug hole for the affected cylinder. Apply regulated air pressure (80-100 psi) to hold the valve on its seat, preventing it from dropping into cylinder when spring is removed. Verify air is holding valve by attempting gentle downward pressure on valve retainer.
   ⚠️If air pressure cannot hold valve (due to poor valve seal), alternative method using rope or specialized tools must be used. Dropping valve into cylinder requires cylinder head removal.
6. 6

   Compress valve spring and remove keepers
   Position valve spring compressor tool on valve spring, ensuring proper engagement with spring retainer and cylinder head surface. Slowly compress spring until keeper groove is exposed. Using magnetic pickup tool or tweezers, carefully remove both valve spring keepers. Place immediately in magnetic tray. Slowly release spring compressor tension.
   ⚠Valve spring keepers are small and easily lost. Work over clean area and use magnetic tray. If keeper falls into engine, it MUST be retrieved before proceeding.
7. 7

   Remove valve spring components
   With spring tension released, remove valve spring retainer, valve spring, and spring seat (if equipped). Inspect all components for damage, unusual wear, or heat discoloration. Check valve stem seal condition; replace if damaged or if sealing lip shows deterioration.
8. 8

   Inspect valve stem and guide
   With spring removed and air pressure still applied, inspect visible portion of valve stem for scoring, wear, or carbon buildup. Check for excessive valve stem-to-guide clearance by attempting lateral movement. Valve should have minimal side play. Clean valve stem with solvent if needed.
   ℹ️Excessive valve guide wear (>0.5mm lateral play) indicates additional service required beyond spring replacement.
9. 9

   Install new valve spring assembly
   Install new spring seat (if equipped) onto valve stem. Position new valve spring with closely-wound coils toward cylinder head (consult spring marking if present). Place valve spring retainer on top of spring, aligning with keeper grooves on valve stem.
10. 10

    Compress spring and install keepers
    Using valve spring compressor, compress new spring until keeper grooves are fully exposed. Apply small amount of grease to keepers to hold in position. Carefully install both keepers into valve stem groove, ensuring they seat properly in retainer slots. Slowly release compressor while verifying keepers remain seated. After full release, tap valve stem tip gently with plastic tool to ensure keepers are fully seated.
    ⚠Improperly seated keepers will eject when engine starts, causing catastrophic valve train damage. Verify keeper installation by attempting to lift retainer with finger pressure.
11. 11

    Remove air pressure and verify valve operation
    Remove compressed air adapter from spark plug hole. Manually press down on valve spring retainer to verify valve moves freely and returns under spring pressure. Check that valve closes completely by listening for sealing sound or using feeler gauge at valve margin.
12. 12

    Reinstall rocker arm
    Verify camshaft is still positioned with lobe pointing away from valve (base circle). Apply light coating of clean engine oil to rocker arm contact surfaces. Position rocker arm onto valve stem and hydraulic pivot. Install rocker arm bolt and torque to specification with cam lobe pointing away from valve.
    ⚠Tightening rocker arm bolt with cam lobe pointed toward valve will preload valve train excessively and may bend valves or damage components.
    Torque spec

    Rocker Arm Bolts30 Nm (22 lb-ft)
13. 13

    Install new valve cover gasket and reinstall cover
    Position new valve cover gasket and spark plug tube seals onto valve cover. Ensure all alignment pins are properly seated. Carefully lower valve cover onto cylinder head, aligning with dowel pins. Install valve cover bolts finger-tight, then torque in proper sequence (center outward) to specification.
    Torque spec

    Cover Bolts22 Nm (16 lb-ft)
14. 14

    Reinstall spark plugs and ignition components
    Apply anti-seize compound to spark plug threads. Install spark plugs and torque to specification for aluminum heads. Reinstall ignition coils in correct positions. Reconnect all electrical connectors, vacuum lines, and breather hoses per documentation from disassembly.
    Torque spec

    Spark Plugs - Aluminum Head20 Nm (15 lb-ft)

Reassembly

1. Reinstall engine covers and air intake components in reverse order of removal
2. Reconnect battery negative terminal
3. Check engine oil level and top off if needed after valve cover reinstallation
4. Clear any diagnostic trouble codes that may have been set during battery disconnection

Verification

• Start engine and listen for unusual valve train noise such as ticking or tapping from affected cylinder
• Allow engine to reach normal operating temperature and verify no oil leaks from valve cover
• Perform cylinder compression test or leak-down test on repaired cylinder to verify proper valve sealing
• Test drive vehicle and verify smooth operation with no misfires or performance issues
• Monitor for any check engine lights related to camshaft position or valve timing over next 50 miles

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

Chasing one of these codes and not sure which part is guilty? Ask a master mechanic about YOUR car →

More procedures for this vehicle