M104 Head Gasket Replacement
This article is a reference for replacing the head gasket on a Mercedes Benz M104 engine equipped with the HFM injection system. Certain details may be specific to M104 implementations in a W124 sedan chassis.
Time | 10 hours |
---|---|
Cost | |
Difficulty | |
Parts Required | |
Applicable models | All HFM injected M104 engines |
Preparation
- Disconnect battery
- Drain oil
- Drain coolant
- Lift and support front half of car to access exhaust system from underneath
- Set engine position to TDC
Remove Front Cover, Belt, and Accessories
- Remove false firewall
- Remove wire harness holder
- Remove valve cover
- Remove and disconnect smog pump / EGR switchover vacuum valve
- Remove fan clutch
- Remove accessory belt
- Remove smog pump
- Remove alternator
- Remove front lifting hook and coolant pipe
- Unplug camshaft advance solenoid and camshaft position sensor
- Remove heater pipe
- Disconnect hose clamp from auxiliary water pump hard line and pull hose off
- Remove 10mm screw from water pump
- Remove 5mm allen screw from idler pulley / fan bracket
- Remove belt idler pulley
- Remove 6x 13mm screws for front top timing cover
- Remove timing chain guide rail pin cover
- 5mm allen screw cover located at bottom right of the upper timing cover
- Use a slide hammer or a puller to remove the timing chain guide rail pin
- Pry upper front timing cover off. Avoid damaging the mating surface with prying tools.
- Remove chain tensioner
- Remove camshaft chain sprocket
Remove Exhaust Manifold
- Remove smog pump / alternator bracket from engine block
- Remove EGR valve
- Disconnect pipe at rear
- Disconnect pipe at manifold
- Remove fasteners at flange and remove
- Disconnect both downpipes from exhaust manifolds underneath car
- Remove downpipes support clamp at transmission
- Remove copper self locking nuts securing exhaust manifolds to cylinder head
- Remove exhaust manifold
Remove Intake Manifold
- Disconnect fuel injectors wire plugs
- Disconnect resonance flap wire plug
- Bleed pressure from fuel rail using test port schrader valve
- Disconnect fuel supply and fuel return hoses
- Remove 5 screws holding fuel rail to intake manifold
- Pull fuel rail off
- Remove remaining screws on intake manifold
- Loosen hose clamps connecting upper and lower manifolds
- Pull air intake away from cylinder head slightly
- Reach down between gap and disconnect knock sensor below cylinder 5
- Remove air intake manifold
Remove Cylinder Head
- Remove EGR support bracket
- Loosen hose clamp on coolant hose at back of cylinder head and pull off hose
- Remove cylinder head bolts, starting with bolt #14 on the outside working towards the center
- Lift cylinder head off engine block. Cylinder head weight approximately 80 lb.
Installing Cylinder Head
- Clean mating surfaces and check for flatness.
- 0.004“ tolerance between front and rear of engine block / cylinder head mating surface
- Clean cylinder head bolt holes
- Set engine timing to 30 degrees BTDC.
- Pistons are in position such that valves will not interfere when adjusted later
- Install new head gasket
- Install cylinder head
- Torque cylinder head bolts
- Lightly coat threads with engine oil for wet torque
- Follow tightening stages, order, and torque specs
- 1st stage: 55 Nm
- 2nd stage: 90 degrees
- 3rd stage: 90 degrees