Engine Mount - Rear

Replacement of the rear engine mount on the M275 6.0L V12 BiTurbo engine to eliminate vibration and restore proper engine support.

Warnings

Tools required

Parts

• Rear engine mount assembly × 1 — A2752401717 or A2752401917

Preparation

1. Park vehicle on level, solid surface and engage parking brake
2. Allow engine and exhaust system to cool completely (minimum 2 hours)
3. Disconnect negative battery terminal and wait 10 minutes for system de-energization
4. Raise vehicle using approved lift points and support on jack stands rated for minimum 3 tons per stand
5. Remove engine undertray panels to access rear mount area
6. Apply penetrating oil to all mount fasteners and allow to soak for 15 minutes

Procedure

1. 1

   Install engine support system
   Install an engine support bar across the engine bay or attach overhead lifting equipment to the engine lifting eyes. Take up slack until support system is bearing minimal weight but engine is stabilized. Do not lift engine at this point, only stabilize it to prevent movement.
2. 2

   Locate rear engine mount
   From underneath the vehicle, locate the rear engine mount positioned between the engine block and the transmission crossmember/subframe. The mount is centered at the rear of the engine, just forward of the transmission bell housing. Use inspection mirror to verify all fastener locations before proceeding.
3. 3

   Support transmission
   Position a floor jack with transmission adapter under the transmission pan. Raise jack until it just contacts the transmission but is not bearing significant load. This prevents transmission from dropping when the rear mount is removed.
4. 4

   Remove mount-to-frame bolts
   Locate and remove the bolts securing the rear mount bracket to the subframe or crossmember. These are typically accessible from underneath. There are usually 2-4 bolts depending on the specific mount configuration. Use 18mm or 19mm socket as appropriate.
   Torque spec

   Engine Mount-to-Frame Bolts75 Nm (55 lb-ft)
5. 5

   Remove mount through bolt
   Locate the large through bolt that passes horizontally through the center of the mount assembly. This bolt secures the mount rubber element. Remove the nut and withdraw the through bolt. You may need to slightly raise or lower the engine using the support system to relieve tension and allow bolt removal.
   Torque spec

   Mount Through Bolt119 Nm (88 lb-ft)
6. 6

   Remove engine mount-to-block bolts
   Access the bolts securing the upper mount bracket to the engine block. These are typically located on the rear face of the engine block and may require a long extension to reach. Remove all bolts securing the mount bracket to the engine. There are typically 3-4 bolts.
   ⚠Ensure engine support system is properly supporting the engine before removing the final mount-to-block bolt.
   Torque spec

   Engine Mount-to-Block Bolts65 Nm (48 lb-ft)
7. 7

   Remove old engine mount
   With all fasteners removed, carefully maneuver the old mount assembly out from between the engine and subframe. You may need to slightly adjust engine height or angle using the support system. Note the orientation of the mount and any shims or spacers for reinstallation.
8. 8

   Inspect mounting surfaces
   Clean the mounting surfaces on both the engine block and subframe using a wire brush. Inspect for cracks, stripped threads, or damage. Check that the engine block mounting threads are clean and serviceable. Replace any damaged hardware.
9. 9

   Position new rear mount
   Position the new rear engine mount assembly in the mounting location, ensuring correct orientation. The mount should match the position and orientation of the removed mount. Install any shims or spacers that were present on the original mount.
10. 10

    Install mount-to-block bolts
    Thread in the bolts securing the upper mount bracket to the engine block. Start all bolts by hand to ensure proper thread engagement. Torque bolts to specification in a cross-pattern sequence to ensure even loading.
    Torque spec

    Engine Mount-to-Block Bolts65 Nm (48 lb-ft)
11. 11

    Install mount through bolt
    Insert the through bolt through the center of the mount assembly. You may need to adjust engine height slightly using the support system to align the bolt holes. Install the through bolt nut and torque to specification.
    Torque spec

    Mount Through Bolt119 Nm (88 lb-ft)
12. 12

    Install mount-to-frame bolts
    Install and hand-tighten all bolts securing the mount bracket to the subframe or crossmember. Ensure the mount is properly seated before tightening. Torque all mount-to-frame bolts to specification in sequence.
    Torque spec

    Engine Mount-to-Frame Bolts75 Nm (55 lb-ft)
13. 13

    Remove support equipment
    Slowly and carefully lower the transmission jack while monitoring engine position. Remove the jack completely. Gradually release tension from the engine support system while observing that the engine settles properly onto all mounts without binding or unusual movement. Remove engine support equipment.
14. 14

    Reinstall undertray and finalize
    Reinstall all engine undertray panels and any heat shields that were removed. Lower vehicle from jack stands. Reconnect negative battery terminal. Start engine and allow to idle while observing mount for proper operation and absence of excessive movement or contact.

Reassembly

1. Verify all mount fasteners are torqued to specification before removing support equipment
2. Ensure no tools or parts are left in the engine bay or underneath the vehicle
3. All undertray panels must be reinstalled to maintain proper aerodynamics and cooling

Verification

• Start engine and verify no unusual vibration at idle or during acceleration
• With engine running, have assistant shift transmission through all gears while you observe mount for excessive movement or contact with surrounding components
• Perform a short test drive with gentle acceleration and deceleration to confirm mount is functioning properly
• Re-inspect all mount bolts after test drive to ensure they remain tight
• Check engine alignment by visually verifying equal spacing on both sides between engine and frame rails

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