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Pelican Technical Article:

Timing Chain Replacement

Steve Vernon

Time:

3-7 hours

Tab:

$220

Talent:

****

Tools:

27mm, 22mm, 19mm socket, grinder, timing chain crimping tool

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Timing chain

Hot Tip:

You need a friend to help

Performance Gain:

Eliminate chain stretch

Complementary Modification:

Valve adjustment

Timing chains stretch over time and will eventually need to be replaced. While replacing a timing chain can be a very daunting task for a DIY mechanic, if you take your time, have the proper tools and follow these instructions you will be fine. Just remember that you will need a helper while preforming this job as you cannot keep tension on the chain and turn the engine by yourself. Setting the TDC marks at the beginning and checking at the end will ensure that you have done the job correctly and ease the fear of the valves being out of time and contacting the pistons. Also do not be in a rush, if something slips because you are hurrying--you may end up adding a lot more time by having to take the front of the motor apart to get everything back in place and lined up.

Over the years your car may have been serviced by multiple people including previous owners and this can lead to parts replaced with different size fasteners and hardware. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches. If something is different on your vehicle please let us know and share your info to help other users. If you have any questions or comments or even a different procedure you would like to share please leave it below and please include your vehicle information.

Begin by disconnecting the ground cable from the battery and placing it somewhere where it cannot make contact with the battery post while you are working.
Figure 1

Begin by disconnecting the ground cable from the battery and placing it somewhere where it cannot make contact with the battery post while you are working.

The timing chain is under the front of the valve cover (red arrow); if this area is dirty give it a good cleaning before you begin as you do not want dirt and debris falling into the front of the chain housing while you are working.
Figure 2

The timing chain is under the front of the valve cover (red arrow); if this area is dirty give it a good cleaning before you begin as you do not want dirt and debris falling into the front of the chain housing while you are working.

I recommend removing the glow plugs (red arrow) as this will help reduce the compression of the engine while you are turning it over and assist in the feeding of the new chain through the motor easier.
Figure 3

I recommend removing the glow plugs (red arrow) as this will help reduce the compression of the engine while you are turning it over and assist in the feeding of the new chain through the motor easier. Please see our article on glow plug replacement for additional assistance.

Next see our article on valve cover gasket replacement to assist you in removing the valve cover and do not forget to install a new gasket when putting everything back together.
Figure 4

Next see our article on valve cover gasket replacement to assist you in removing the valve cover and do not forget to install a new gasket when putting everything back together.

If your vehicle is equipped with an EGR valve you will need to remove the EGR tube (red arrow) to access the chain tensioner behind the plate (yellow arrow).
Figure 5

If your vehicle is equipped with an EGR valve you will need to remove the EGR tube (red arrow) to access the chain tensioner behind the plate (yellow arrow).

You do not need to remove everything I did just enough to get access to the chain tensioner bolt (red arrow).
Figure 6

You do not need to remove everything I did just enough to get access to the chain tensioner bolt (red arrow). Use a 19mm socket and remove the bolt.

This is a very good time to replace the chain tensioner spring (as you can see in the photo how much they can compress over the years).
Figure 7

This is a very good time to replace the chain tensioner spring (as you can see in the photo how much they can compress over the years).

Figure 8

Use a 22mm wrench or socket and turn the engine until the mark on the timing sprocket lines up with the mark on the cam support (red arrow) at TDC

Check with the witness mark on the dampener (red arrow) and they should both be at TDC or Top Dead Center.
Figure 9

Check with the witness mark on the dampener (red arrow) and they should both be at TDC or Top Dead Center.

Stuff some rags around the opening in the top of the motor to protect anything from falling in and use a grinder to cut a link in the chain.
Figure 10

Stuff some rags around the opening in the top of the motor to protect anything from falling in and use a grinder to cut a link in the chain.

Separate the links in the old chain making sure to always keep tension on both sides of the chain.
Figure 11

Separate the links in the old chain making sure to always keep tension on both sides of the chain. If you let the chain slip and skip a tooth or drop it down into the housing you will need to take the front of the motor apart to get everything sorted.

Attach the end of the new chain to the old as you are facing it right side of the old chain.
Figure 12

Attach the end of the new chain to the old as you are facing it right side of the old chain.

While keeping tension on both sides of the chain have your assistant turn the motor by the main crank bolt clock-wise until the new chain is drawn all the way through.
Figure 13

While keeping tension on both sides of the chain have your assistant turn the motor by the main crank bolt clock-wise until the new chain is drawn all the way through.

Install the new master link attaching the new chain together.
Figure 14

Install the new master link attaching the new chain together.

Use the proper crimping tool and crimp the master link onto the chain; do NOT try and do this with Vice-grips or some other tool; rent or purchase the proper tool or you run the risk it grenading your motor down the road.
Figure 15

Use the proper crimping tool and crimp the master link onto the chain; do NOT try and do this with Vice-grips or some other tool; rent or purchase the proper tool or you run the risk it grenading your motor down the road.

Once everything is buttoned up line up the cam sprocket markings at TDC again (red arrow).
Figure 16

Once everything is buttoned up line up the cam sprocket markings at TDC again (red arrow).

If the balancer pulley is also on TDC congratulations you have successfully replaced your timing chain.
Figure 17

If the balancer pulley is also on TDC congratulations you have successfully replaced your timing chain. Installation of everything else is the reverse of removal.

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