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Pelican Technical Article:

Valve Adjustment

Steve Vernon

Time:

1-3 Hours

Tab:

$5 to $25

Talent:

**

Tools:

Feeler gauges, 22mm, 14mm bent wrenched (2)

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Valve cover gasket

Hot Tip:

Take your time

Performance Gain:

Proper functioning valve train

Complementary Modification:

Replace valve cover gasket

One of the most important yet overlooked maintenance procedures on the Mercedes W123 is the valve adjustments. The valves need to be adjusted properly otherwise they may not open enough to draw sufficient air into the combustion chamber and/or close completely to create an effective seal giving correct compression in the chamber. These clearances are set by the space between the tappet and cam lobe when the lobe is furthest away from the tappet and there is no pressure between the lobe and tappet. If you have a tired running motor and have never adjusted your valves you may find that something as simple as adjusting the valves can make the motor feel brand new with a remarkable increase in power. Pelican recommends adjusting your valves every 12,000 miles or once a year. It doesn't take long to do, especially after you have done it more than once and for the cost of a new valve cover gasket it's a great way to insure the performance of your engine. Before you begin this procedure, please see our article on Valve Cover Gasket Replacement.

You will be working in a confined space and will need two 14mm wrenches that are bent on an angle. These are easy to make and we will show you how so you can save some money and not have to buy the special Mercedes wrenches.

IMPORTANT: Make sure the engine is stone cold before adjusting the valves; in theory it should sit over night before attempting to do this. The valves' train and cams are susceptible to thermo-expansions and the adjustments have to be done with everything cold.

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.

You will need to remove the valve cover gasket to adjust the valves so please see our article on valve cover gasket replacement for additional assistance.
Figure 1

You will need to remove the valve cover gasket to adjust the valves so please see our article on valve cover gasket replacement for additional assistance. Remember the engine must be stone cold before adjusting the valves.

You are going to be turning the cam to adjust each lobe and valve.
Figure 2

You are going to be turning the cam to adjust each lobe and valve. You can turn the cam by using a 27mm wrench on the large nut on the crank dampener--always make sure you rotate the cam clock-wise. You are going to be measuring the distance between the tappet (yellow arrow) and the cam while the lobe is at the very top (red arrow) for each valve.

For the intake valve you will need a .
Figure 3

For the intake valve you will need a .004 inch or .102mm feeler

The exhaust uses a .
Figure 4

The exhaust uses a .012 inch or .305mm feeler gauge.

Due to the tight space between the valves, cam and injectors you will need two 14mm wrenches for adjusting and locking the nuts.
Figure 5

Due to the tight space between the valves, cam and injectors you will need two 14mm wrenches for adjusting and locking the nuts. The wrenches need to be bent at 30-40 degree an inch or two away from the opening. While you can buy some very expensive tools just for this job, if you have a vice and a torch you can make your own. You are going to be working around an open flame and getting the metal very hot so make sure you take all the necessary precautions: like good gloves, eye protection, no loose clothes and have a fire extinguisher handy--make sure it is full and that you know how to use it. Place your wrench with the end you are going to bend into the vice.

Use your torch and heat the shaft of the wrench where you want to bend it.
Figure 6

Use your torch and heat the shaft of the wrench where you want to bend it. Let the metal get really hot, it will make bending it much easier.

With the metal really hot, place a piece of pipe over the wrench and bend it to the angle you need.
Figure 7

With the metal really hot, place a piece of pipe over the wrench and bend it to the angle you need. Never try and bend it by hand unless you have welding gloves. The pipe will protect your hands, increase the mechanical advantage and help protect you if the wrench breaks.

There are two adjusting nuts on the valves.
Figure 8

There are two adjusting nuts on the valves. The upper nut which sets the distance between the cam and tappet (red arrow) and the locking nut (yellow arrow) you use to tighten them up together once the height has been adjusted. If the valve adjustment is too tight to begin with you will need to loosen the lower tightening nut first, where as if the distance is too lose you can start by going up on the upper nut.

This photo shows the series of intake valves (white letter I) and the exhaust valves (red letter E).
Figure 9

This photo shows the series of intake valves (white letter I) and the exhaust valves (red letter E). Do not forget they have different settings.

With the cam lobe pointing straight up you want to be able to put the appropriate feeler gauge between the tappet and cam and there should be a slight drag.
Figure 10

With the cam lobe pointing straight up you want to be able to put the appropriate feeler gauge between the tappet and cam and there should be a slight drag. You will get a feel for it as you go but the feeler should slip in and out with a slight tug. If it will not go in the valve is too tight and if it just falls in with no resistance the valve is too lose.

The locking nut on the bottom is thinner than the adjusting nut (red arrow) on the top.
Figure 11

The locking nut on the bottom is thinner than the adjusting nut (red arrow) on the top. Make sure that the wrench you use on the bottom is thin enough (yellow arrow) that is does not block you adjusting the top nut independently.

You can now use your two wrenches and feeler gauge to adjust and check the valves.
Figure 12

You can now use your two wrenches and feeler gauge to adjust and check the valves. Do not get frustrated if the clearance changes while you are tightening the lock and adjusting nuts down, this is common to everyone and you will get the hang of it as you go along. Once the valve is adjusted, rotate the cam and move on to the next valve, remembering to use the right feeler gauge depending on whether it is intake or exhaust. Once they are all adjusted, I like to do a final check on each with the feeler gauge before buttoning everything back up.

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Comments and Suggestions:
charmalu Comments: In picture #2 you mention to rotate the engine by the large nut on the cam shaft.
I have been on this Form since 07, and it has been mentioned this is a NO NO. It is mentioned over and over to rotate the engine with a 27mm Socket and turning the Crank Bolt.
As per the FSM, Service Manual Engine 617.95 Turbo Diesel.
Section 05 Engine Timing, Valves.
Page 05.8-210/4
Attention!
Do not rotate engine at fastening bolt of Camshaft Sprocket
Do not rotate crankshaft in reverse.

I use a 7/8" Gear Wrench on the Steering Pump nut to rotate the engine. FSM I havent seen this mentioned yet doesnt mention it is a no no to do, but plenty on the Forum say this is bad. Been doing it a long time.

I use the Hazet bent wrenches, work great. Not taking your car to a shop one time will pay for the wrenches.
There is a 3rd wrench to hold the valve spring keeper. Some times the whole valve will turn if the lock nut is jambed tight to it.
The way you made your wrenches, looks like it would be difficult to ge leverage.

Your 9th picture, I wipe off the oil tube and write "I" OR "E" with a black felt tip pen to keep me organized.



April 5, 2016
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 

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