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Pelican Technical Article:

Head Gasket Replacement

Steve Vernon

Time:

14 hours14 hrs

Tab:

$40 to $500

Talent:

*****

Tools:

All of them

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

New head gasket set, head bolts and washers

Hot Tip:

Get a friend and a hoist to help you lift the head

Performance Gain:

Longer engine life

Complementary Modification:

Flush your cooling system and replace your radiator hoses

There are several signs that you are in need of a new head gasket. The most common amongst them is the mixing of your oil and coolant. If you have had a water pump or thermostat fail, and your car overheated, there is a very good chance you are going to be looking at performing this job, as the extreme temperatures associated with an over heated engine can damage both the head and its gasket.

Replacing your head gasket might be the biggest job you will attempt on your car short of rebuilding the entire engine. It is not a quick or easy job, but can be done by a DIY mechanic if you take your time, have the right tools and follow the instructions. This job can take a few days for a novice, so make sure you have the car in a secure and weather safe area before you start. You are going to be opening up the engine and may even be sending the head out for repairs, so you don't want to be working outside when it starts to rain.

I can not stress this enough: get a digital camera and take lots of pictures before and during this job, document wire and vacuum routing plus anything you feel unsure of, this can only help when it comes time to put everything back together.

There are several steps that need to be preformed on other parts of the car before you begin removing the cylinder head. We have covered all of these in separate articles so I am not going to include them here, as this will be a long enough project as it is. Please refer to all the other articles as you work through this project.

First, safely raise and support your vehicle and put the hood into the service position.

Begin by removing the ground cable (red arrow) from the battery and placing it somewhere where it cannot accidentally come in contact with the battery post.
Figure 1

Begin by removing the ground cable (red arrow) from the battery and placing it somewhere where it cannot accidentally come in contact with the battery post.

Drain the coolant, please see our article on coolant flush and fill for additional assistance.
Figure 2

Drain the coolant, please see our article on coolant flush and fill for additional assistance.

Remove the turbo charger and components by following the steps in the turbo removal article.
Figure 3

Remove the turbo charger and components by following the steps in the turbo removal article.

Next is the article on removing the trap and EGR valves if your car is equipped with them.
Figure 4

Next is the article on removing the trap and EGR valves if your car is equipped with them.

Remove the intake and exhaust manifold along with the thermostat housing, please see our article on these procedures.
Figure 5

Remove the intake and exhaust manifold along with the thermostat housing, please see our article on these procedures.

Remove the cam and tower; this article will include steps to remove the throttle linkage and valve cover.
Figure 6

Remove the cam and tower; this article will include steps to remove the throttle linkage and valve cover. From this point on the timing chain must be kept under constant tension by pulling it and anchoring it somewhere to the side of the engine.

Remove the fuel lines from the pump to the injectors along with disconnecting all of the wiring to the glow plugs and temperature sensors.
Figure 7

Remove the fuel lines from the pump to the injectors along with disconnecting all of the wiring to the glow plugs and temperature sensors. Please see our articles on these procedures for additional information.

Disconnect the hoses from each injector and using an injector removal socket or a deep 27mm remove the injectors.
Figure 8

Disconnect the hoses from each injector and using an injector removal socket or a deep 27mm remove the injectors.

If your injector comes out wet it will not be a good sign of things to come.
Figure 9

If your injector comes out wet it will not be a good sign of things to come.

Use a 10mm wrench and remove the single bolt that holds the tube at the rear of the head (red arrow).
Figure 10

Use a 10mm wrench and remove the single bolt that holds the tube at the rear of the head (red arrow).

Disconnect the heater hose from the left rear of the head (yellow arrow).
Figure 11

Disconnect the heater hose from the left rear of the head (yellow arrow).

You are going to need to remove the cruise control unit; base and mounting plate so please see our article on cruise control replacement for further assistance.
Figure 12

You are going to need to remove the cruise control unit; base and mounting plate so please see our article on cruise control replacement for further assistance.

Disconnect the lines and remove the fuel filter and filter mounting bracket (red arrow).
Figure 13

Disconnect the lines and remove the fuel filter and filter mounting bracket (red arrow).

Remove the power steering pump from the front of the motor with the lines attached as you are going to need to remove the power steering/fuel filter mount.
Figure 14

Remove the power steering pump from the front of the motor with the lines attached as you are going to need to remove the power steering/fuel filter mount.

Take your new gasket and trace an outline of it on a cardboard box, this way you will have a good way to keep track of the head bolts.
Figure 15

Take your new gasket and trace an outline of it on a cardboard box, this way you will have a good way to keep track of the head bolts. While some people say you can reuse them I ALWAYS replace the head bolts, after all you are going to a lot of time and trouble to change out the head gasket so $50 for new head bolts and washers is good insurance.

Remove the Allen fasteners from the front of the head and do not forget the two inside the timing chain opening (red arrow).
Figure 16

Remove the Allen fasteners from the front of the head and do not forget the two inside the timing chain opening (red arrow).

I highly recommend you purchase a 140mm long 12mm triple square for the head bolts.
Figure 17

I highly recommend you purchase a 140mm long 12mm triple square for the head bolts.

The bolts sit down in the valve train and it is very difficult to seat a standard triple square and extension.
Figure 18

The bolts sit down in the valve train and it is very difficult to seat a standard triple square and extension. You do not want to strip one of the bolts or you will be in a world of trouble trying to get it out.

Using your 140mm triple square and a long breaker bar, remove the head bolts according to the pattern supplied.
Figure 19

Using your 140mm triple square and a long breaker bar, remove the head bolts according to the pattern supplied. The head sits on locating dowels so once it is loose it will not slip off. Loosen all of the bolts according to this pattern before you fully remove them.

Attach a chain to the front and rear lift eye hooks or get a really strong friend to help.
Figure 20

Attach a chain to the front and rear lift eye hooks or get a really strong friend to help. If you attempt to lift the head and it doesn't move you can try placing a 2X4 (red arrow) along the side and hitting the wood with a hammer to help dislodge it.

Lift the head straight up a small amount and check that you have not missed anything that still might be connected to it then lift it up and off the motor.
Figure 21

Lift the head straight up a small amount and check that you have not missed anything that still might be connected to it then lift it up and off the motor.

The front cylinder (red arrow) is what they should look like with dry carbon on the crown.
Figure 22

The front cylinder (red arrow) is what they should look like with dry carbon on the crown. If your piston crowns are shiny it is because they have been getting a good pressure wash from the coolant mixed in the combustion chamber and this is not good. The fact that we had coolant and oil sitting in the cylinders (yellow arrows) shows the extent of the failed head gasket.

While it is easy to spot the areas on our head where the gasket failed (red arrow) sometimes this is not so easy to see; we always recommend sending the head out for cleaning and inspection as lots of problems with a head cannot be spotted with the naked eye and if they are not corrected it will just fail again and you will be going through all of this again shorty.
Figure 23

While it is easy to spot the areas on our head where the gasket failed (red arrow) sometimes this is not so easy to see; we always recommend sending the head out for cleaning and inspection as lots of problems with a head cannot be spotted with the naked eye and if they are not corrected it will just fail again and you will be going through all of this again shorty.

Remove the old gasket.
Figure 24

Remove the old gasket.

You are going to really need to clean the top surface of the block so you can get a good clean flat mounting surface.
Figure 25

You are going to really need to clean the top surface of the block so you can get a good clean flat mounting surface. Do not use anything that could gouge or mare the surface as this will just lead to gasket failure again. Once everything is cleaned up make sure to use a shop-vac and clean up inside the cylinders. You cannot be too clean when working on the head.

Installation is the reverse of removal.
Figure 26

Installation is the reverse of removal. When installing new head bolts lightly lubricate them with clean engine oil. Insert them finger tight first and then tighten them according to this pattern. Check with the specs on your bolts as some are different. Most will require multiple steps with a certain time in between each torque to let everything settle and the heat that is caused by the torqueing to dissipate.

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