Mercedes-Benz W140 5.0L M119 Engine

Mercedes-Benz W140 5.0L M119 Engine & 722.5 Gearbox Rebuild: A Guide to Restoring the Legend
The Mercedes-Benz W140 S-Class (1991–1998) with the 5.0L M119 V8 engine and 722.5-series 5-speed automatic transmission represents the pinnacle of 1990s luxury and engineering. A rebuilt engine and gearbox revitalize this iconic sedan, restoring its silken power delivery and timeless refinement. Below is a comprehensive breakdown of the components, rebuild process, and considerations for owners or enthusiasts.

1. The M119 5.0L V8 Engine: Overview

• Displacement: 4,973 cc (5.0L), naturally aspirated.
• Power Output: 322 hp (DIN) and 347 lb-ft of torque (1990s-era ratings).
• Key Features:
  • Double overhead camshafts (DOHC), 32 valves.
  • All-aluminum construction for reduced weight.
  • Bosch LH-Jetronic fuel injection with hot-wire MAF sensor.
  • Hydraulic lifters for quiet operation.
  • AMG Connection: The M119 was later tuned by AMG for the 500 SL (R129) and homologation-special cars like the E 60 AMG.

Common Rebuild Triggers:

• Biodegradable Wiring Harnesses: Insulation degrades over time, causing electrical gremlins (critical to replace during rebuild).
• Oil Leaks: Valve cover gaskets, camshaft seals, and front crank seal.
• Timing Chain Guides: Wear can lead to chain slap or skipped timing.
• Cylinder Head Issues: Cracked heads (rare but possible in overheated engines).

2. The 722.5 5-Speed Automatic Transmission

• Model: 722.5 (5G-Tronic), a robust, adaptive gearbox designed for the M119’s torque.
• Key Features:
  • Smooth, torque-converter-driven shifts.
  • “Winter mode” (2nd-gear start) and manual shift capability.
  • Integrated electronic control unit (TCU) for adaptive shift logic.

Common Rebuild Needs:

• Valve Body Wear: Sticky solenoids or worn shift valves causing harsh shifts.
• Torque Converter Clutch (TCC) Failure: Causes slippage or shuddering.
• Seal Degradation: Input/output shaft seals and front pump seal leaks.
• Clutch Pack Wear: Requires disassembly and replacement of friction discs.

3. Rebuild Process & Upgrades

Engine Rebuild Steps:

1. Disassembly: Inspect crankshaft, pistons, and bearings for scoring.
2. Machining: Deck the block, hone cylinders, and polish the crank.
3. Critical Replacements:
   • Timing chain, guides, and tensioner.
   • Full gasket/seal kit (Elring or Victor Reinz).
   • Rewired Harness: Replace with modern insulation (e.g., Kabelwerk Kerpen harness).
4. Performance Upgrades (Optional):
   • AMG-spec camshafts (from period E 60 AMG models).
   • High-flow intake/exhaust (e.g., Renntech headers).
   • ECU remap for sharper throttle response (+15–20 hp).

Transmission Rebuild Steps:

1. Overhaul Kit: Includes seals, clutch packs, and gaskets.
2. Valve Body Rebuild: Replace solenoids and polish bores.
3. Torque Converter: Rebuild or replace with a reinforced unit.