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.

1. Disconnect battery
2. Drain oil
3. Drain coolant
4. Lift and support front half of car to access exhaust system from underneath
5. Set engine position to TDC

1. Remove false firewall
2. Remove valve cover
3. Remove and disconnect smog pump / EGR switchover vacuum valve
4. Remove fan clutch
5. Remove accessory belt
6. Remove smog pump
7. Remove alternator
8. Remove front lifting hook and coolant pipe
9. Unplug camshaft advance solenoid and camshaft position sensor
10. Remove heater pipe
    1. Disconnect hose clamp from auxiliary water pump hard line and pull hose off
    2. Remove 10mm screw from water pump
    3. Remove 5mm allen screw from idler pulley / fan bracket
11. Remove belt idler pulley
12. Remove 6x 13mm screws for front top timing cover
13. Remove timing chain guide rail pin cover
    1. 5mm allen screw cover located at bottom right of the upper timing cover
14. Use a slide hammer or a puller to remove the timing chain guide rail pin
15. Pry upper front timing cover off. Avoid damaging the mating surface with prying tools.
16. Remove chain tensioner
17. Remove camshaft chain sprocket

1. Remove smog pump / alternator bracket from engine block
2. Remove EGR valve
   1. Disconnect pipe at rear
   2. Disconnect pipe at manifold
   3. Remove fasteners at flange and remove
3. Disconnect both downpipes from exhaust manifolds underneath car
4. Remove downpipes support clamp at transmission
5. Remove copper self locking nuts securing exhaust manifolds to cylinder head
6. Remove exhaust manifold