How to Adjust the Valves on a Diesel 617-engine

The valves should be adjusted at regular intervals every 15.000-20.000km to be at peak performance and save on fuel economy. These old engines for the W123s don’t have automatic valve adjusting like later models and needs therefore regular adjustment. The valve clearance has to be exactly to specifications to ensure you get the peak performance out of the engine. Especially for the diesels where you have relatively few horse powers to play around with from the beginning (the biggest 3.0L non turbo only has 88hp). The valve adjusting procedure is actually quite simple and can be done in an afternoon, but it needs some patience to get it just right when it’s your first time. This is why many mechanics shops do not necessarily get it right all the time due to their time pressure, so you should just do it yourself: Save money and have the peace of mind knowing that the job is done right!


The only special tools needed are two valve adjusting wrenches and a feeler gouge. A very good kit of these tools can be bought over at, I highly recommend to check their site and kits out, they are highly prtofessionals!

Get a new valve cover gasket, the old ones are always leaking after some years and this is a good time to change the inexpensive gasket.

If the valve cover bolts have missing wave washers, obtain spare ones as well.

valve adjustment kit for diesel engine
Special tools, valve adjusting wrenches and feeler gauges.

The valve adjustment needs to be done when the engine is cold and have a temperature of around 20°C. The valve clearance specifications are set at this temperature, remember your physics that metal expands when warm and you will get a tighter gap between the valves, oppositely the gap will be too small when the engine is very cold. So you can’t just do this after driving home from work. The easiest thing is just to leave the car over night before doing it. The valve adjustment can be done when the engine is warm with different valve gap specifications, but I wouldn’t recommend it since you might burn yourself and the temperature of the engine would slowly get lower during the adjustment process so you have to be very quick about the adjustment. We both know that is not going to happen so just do it when the engine is cold…

Mercedes 617 engine in W123
The 617 engine, just to make sure
Adjustment Procedure

For accessing the valves, the valve cover has to be removed. For better access other components attached to the valve cover have to be removed before. Remove the air filter housing which is attached with 3 bolts. Since this particular 300TD has a manual 5-speed transmission, there are no vacuum lines and a complex throttle linkage attached to the top of the valve cover, so the removal is more straight forward than with an automatic. If you have the automatic, then take a picture so you remember where all the linkages and lines went.

For accessing the valves, the valve cover has to be removed and for better access other components attached to the valve cover have to be removed too. Since my 300TD has a manual 5-speed transmission, there is no vacuum lines and a complex throttle linkage attached to the valve cover, so the removal is more straight forward. I begin with removing the air filter housing, it's only secured with 3 bolts.
Air filter housing removed

After removing the throttle linkage attached to the cover, start unbolting the valve cover itself. It is attached it four 13mm bolts.

valve cover bolts 617 engine
valve cover bolts, not the small washers, which are special wave washers, in 99% of the cases they are missing. Obtain spare ones before doing this job

Pull up on the cover and then you can see the valve springs and the upper components of the engine. Sometimes it is a little tricky to pull the cover off so just wiggle it side to side until it is off.

Time to prepare the valve adjustment. Make absolutely sure that the engine is cold, it should have the ambient temperature at about 20°C when adjusting the valves. For the 617 engine WITHOUT a turbo (also called non-turbo versions indicated by only the D or TD if you have stationwagon, if you have a turbo it says Turbo-Diesel in the designation), the intake valves needs clearing of 0,10mm and the exhaust valves needs a clearing of 0.30mm. There are 10 valves in total, 2 for each of the 5 cylinders, to determine which valves are intake or exhaust valves, just look at the corresponding manifolds. I highly recommend to draw a simple valve chart and cross out which valves you have adjusted to leave all confusions out. I hate doing things twice..

For accessing the right position on the valves, you have to turn the camshaft. For turning the camshaft, you have to basically turn the whole engine. How do you turn the engine over? And can you do this by hand? Sure you are strong enough, remember back in the days they started the cars by hand with turning the crank shaft. So that leaves you two options:

  1. The first option is turn it by hand on the crankshaft pulley bolt, I think this is the easiest and fastest way to do it. But it requires some use of muscles and taking care of not scratching the hands on the fan or the radiator, because here the space is quite tight. ALWAYS turn the crank clockwise when looking from the front of the engine, never even think about turning it the other way!!!
  2. The other option is to reconnect the starter motor so you can turn the crank slowly with the ignition, this procedure needs you to crawl under the car and play with the wiring on the starter motor. Remember you don’t want to start the engine so the starter has to engage slowly.

When adjusting the valve clearances, the cam lobes needs to be pointing straight upwards from the valve you are working on. This is why you need to turn the crank to get the right position of the camshaft. Use the feeler between the cam lobes and the rocker arm, there should be a slight drag when you move the feeler in and out, just between squeezing and no resistance. The are two bolts on top of each valve. Use the valve adjusting wrenches to adjust the valves by loosening the top nut and the actual adjusting is done with the lower nut. Turn the lower nut clockwise to make the gap bigger and anti clockwise to make the gap smaller. It takes some tries to get it right the first time because the adjustment is very sensitive, the tightening of the top bolt will in fact influence so this needs some practice, just be patient. It is easier to have a companion that continuously checks the clearance when you do the adjustment to get it right. I have only done it alone though so it’s not impossible. When are alone, you have to always recheck your own work with the feeler after adjusting and it takes a couple attempts to get it right. Remember to tighten the top locking nut after adjusting and recheck the clearance.

valve adjusting 617 engine
Valve adjustment, use the feeler when the cam lobes are pointing upwards from the valve.

After each valve, turn the engine and do the next one, since the lobes are not in order one after another, note down which valve you just adjusted so you don’t have to spend all night turning the engine over a million times.

When all 10 valves are adjusted, replace the valve cover gasket to prevent leaks. Don’t over tighten the  valve cover bolts, let the gasket do the sealing and not brute force. Put all the other parts together and have a test drive, and most likely you will feel an increase in performance and acceleration. That is usually the case if all valves were to tight before the adjustment and is a indication of neglected valve adjustment maintenance.


How to Replace Brake Calipers/ Pads/rear rotor

The brake fluid is hygroscopic, which means it will absorb water moisture over time. This is the primary reason for changing brake fluid regularly, at least once every two years. When the brake fluid contains water it will make the internals of your brake calipers start rusting and the pistons will begin to stick, leading to overheated wheels that can; worst case cause fire due to overheating the rotor and/or make your wheels drag like you are slightly braking all the time.

So if you have sticking brake pistons and they are beyond repair, then a caliper change is necessary. Thankfully the calipers for the w123 are not that expensive, where the rear ones are quite cheaper than the front ones. I will go over how you change the caliper for the rear, but the procedure is nearly exactly as the same the front. If you have never worked on your brakes, then I recommend having someone around that is familiar with brake change or you read upon the topic very seriously and prepare thereafter. This job is one of those highly critical areas where you have to make sure you do it right before you start driving! That aside, working with brakes are in fact quite simple and when you have done it a couple of times it will be no stress at all.

You should consider brake maintenance your primary safety concern:

  • Change brake pads before they are worn out
  • Do regular brake fluid changes
  • Inspect wear on the rotors, check for excessive “lip”
  • Inspect flexible brake hoses for wear
  • Inspect brake hard lines for corrosion
  • Feel that the brake booster is working

If you are changing the calipers, they have to be done in pairs i.e. on both sides of the car. The same applies for the brake pads.

Take care of your health, you should wear a dust mask to prevent breathing in brake dust particles. Also to avoid the dust altogether, after taking the wheel off -> Use soapy water and a big brush to clean down the caliper and around the rotor and brake shield. This will prevent dust from floating around in the air while working.

  • Brake bleeding kit or a companion to work the pedal
  • Clear tube
  • Caliper if you are changing them
  • Brake pads, they are stupid cheap and not to change them when working on the brakes are dumb
  • New brake sensors for the front pads
  • New flexible brake hoses if they are more than 10 years old
  • Locktite thread glue
  • Consider changing the rotors if they have a large lip
  • Brake pad grease, i.e. Lubro Moly LM508
  • Brake fluid
  • Necessary tools and torque wrench
Procedure Removal

Apply braking pedal, put a stick or something so it is depressed throughout the job, this will prevent some braking fluid loss. Jack up the necessary wheels and put your car on jack stands. Take off the wheel and clean the caliper area with soapy water.

rear caliper
Old caliper, looks ok from the outside, but in fact completely useless and sticking pistons. Also completely lacks pad rattle spring, probably rusted a long time ago.

The brake calipers can be of different types primarily of ATE or Bendix, they are quite similar though and if you bought a pair of new ones without knowing the type you had it does not really matter when you are throwing out the old ones anyway. They use the same fitting bolts, brake hose inlet and brake pads. The major difference is the construction of the brake pad locking system and using different internal seals.

caliper front
Front caliper with brake pad sensor. Note the right sensor is missing

If working on the front, start by removing the two brake pad sensors. The brake pads are secured with two locking pins and a spring is holding the pads down to prevent rattling. The two locking pins are either hold in by a clamping spring so you have to use a long and thin driver to punch it in, or they can be held in place by a security pin on the end. I mostly encountered the ones you have to use the long driver and a hammer to get out.

old and new brake pads compared
A good reason to change the brake pads, completely worn beyond the pad sensor, which didn’t quite give a pre warning. Brakes went through Norwegian mountains and started scraping on the old rotor. Good thing to have manual gear and drive home without using the brakes like a pro.

When the pins are removed, use a screwdriver or maybe you have brake pad remover tool to pull the pads out. If you can’t get the pads out because they are stuck due to rust, then you have to get on disconnecting the caliper and use a hammer to knock off the entire caliper. This is frustrating when you are only changing the pads. (Happened to me once, look under)

front caliper stuck, remving with a hammer
Removing stuck pads by unbolting the caliper and hammering the entire caliper off

If you are only taking off the calipers to do this or changing the rotors and not the calipers, then you can go on undoing the caliper bolts without taking off the brake hose, in that way you don’t have to bleed the brake system. Taking off the calipers are necessary if you are for example changing the struts, the rear drive shafts or something that require you to have the trailing arm fully suspended which will put excess pressure on the brake hose. Don’t leave the caliper hanging from the brake hose since it can damage it! Tie it up to something under the car with some zip ties.

If you are changing the brake calipers, then start by taking off the brake hose. If you are changing the brake hose or not, start by using a hose clamping tool (which are made for this purpose and not pliers or similar!) on the brake hose to prevent brake fluid spillage and emptying the fluid reservoir. Also if you are dealing with the front calipers, then remove the brake pad sensor wiring harness from the caliper.

clamping the brake hose with clamper
Preventing fluid spill with a hose clamping tool, Don’t use other sharp tools if you are planning on using the hose later.

Now you can start undoing the caliper bolts, there are two of them and they are on quite tight.

By now you have successfully removed the caliper, not so difficult eh? The choice is yours to change the brake rotors, my guess is that if you are replacing the calipers, the rotors are probably worn a lot too. The front brake rotors needs quite a procedure to be replaced (I will cover that in another how to..). The rear ones are easy to pull off. Disengage the parking brake. Sometimes you can just pull out the rear rotors by force, but often they stick to the parking brake shoes. They can be adjusted to be less tight by turning a star screw through one of the wheel hub bolt holes. It should be 45° from the diagonal towards the front of the car, use a torch to peek in. Once located, use a thin flat headed screw driver to turn the screw until it gets loose. I can’t recall if it’s up or down, you will figure it out quite fast. This means that you have to tighten it once you put on the rotor again or your parking brake is not going to be working.

Now you can go on removing the brake hose, here you have to be careful since the brake line can break or you can damage the fitting if the brake hose is stuck or completely rusted. Try to loosen it, but if it will not come loose without the use of excessive force, leave it and put the other new parts on. Better to at least have a car you can drive than a broken brake hard line, instead take the car to a workshop later that can replace your hose and possibly change your old brake lines as well.

Be fast since brake fluid is going to come out when you remove the hose and clamp.

old and new rear caliper compared
Comparing old caliper with new one, also new brake hose.

Put that brake hose on fast and tighten, then put on the hose clamper on again. Now check your brake fluid reservoir and refill until slightly under maximum mark. Leave the cap off.

Put on your rotor again and adjust the parking brake with the star nut. Check the tightness by turning the wheel, it should have a light drag to it.

When putting back the caliper again, the bolts need to have a little bit of thread locker applied to the threads since there are no washers or other methods to secure the bolts from coming loose. Remove old crud on the threads before. Liining up the caliper while finding the threads can be a bit tricky, especially while trying to do it before the thread locker dries, so apply thread locker to only one bolt at a time. Use your hand to put the bolt in by hand top ensure you don’t cross thread. Do the final tightening with a torque wrench, since over tightening might lead to the bolt head snapping off and then you have no brake calipers going down the road…

new rear caliper
New rear caliper, yeeeiii!

Put on the the brake hose, don’t over tighten. Now you might have to push in the pistons, this can either be done with a brake piston tool or using the end of a crowbar leaning against the rotor to push it in. This is why the fluid level cap should be off and the reservoir not completely full, since there might be fluid that can squirt all over when you push the pistons in. Check the level and extract some fluid if it’s getting over maximum.

Put a little pad grease on the sides of the pads where it sits in the caliper housing then put them in. Fit the pad spring and retaining pins. Make sure the bleed nipple is tighten. Now the calipers are ready to be bled from air.

Brake bleeding

Fill up the reservoir to maximum. When you have been doing caliper changes on only two wheels, then you don’t necessarily have to bleed the whole system since there are two circuits. You should start by bleeding the caliper furthest from the reservoir and work your way towards the closest to the reservoir. It is very important that the reservoir do not get empty while doing the bleeding, which means air has gotten into the system from the top and you have to do a full system bleeding on all calipers. Always check the reservoir often and refill after every bleed of one caliper!

Bleeding kit:

If you have a brake bleeding kit, then put the tube over the nipple and start pumping until you get vacuum, open the bleed nipple slightly until you see only clear fluid without bubbles coming out then shut the nipple again. Refill the reservoir until max. Repeat with same procedure on the next wheel you have been disconnecting the caliper.

Without bleeding kit, but with helper:

You at the caliper with the bleed nipple is the dictator, the helper at the brake pedal is the slave which must not do anything without permission and your commands, otherwise you have to start the bleeding over. You need a clear tube running in to a bottle with fluid where the lower end of the tube is submerged in fluid. You should be able to see clearly the state of the fluid coming out of the tube. The clear tube needs a tight fit over the nipple so no air can come in and give you false readings.

You start out with the nipple shut and the brake pedal disengaged. You open the nipple and you give the helper permission to depress the brake pedal fully, break fluid will come out, you then shut the nipple again while the brake pedal is depressed. After the brake nipple is tight, you give the helper to release the brake pedal. Now you repeat the process slowly and controlled, and you clearly check if the fluid coming out is with or without air bubbles. You also have to make sure the reservoir is not becoming empty. When no air bubbles can be seen coming with the fluid, the caliper is bled and you can move on to the next wheel.

Checking brakes after bleeding:

When done make sure the reservoir is on the maximum mark. Put on the cap again and feel your brakes. The brake pedal should be completely stiff after a few pumps and not get soft when you hold it down under force. Start by doing some braking while going slowly at the parking lot. Then test once at higher pace. If your brake pedal feels completely stiff and your car stops immediately after hard braking, then job well done! If your brake feels squishy then you have to restart the bleeding procedure.


How To Remove the Door Panel on W123

This is an easy job, but unless you know all the hidden screws and plastic tabs you might break the interior, and there are no new interior parts on the market, take care of your door panels.

You need to take off the door panel every time you need to lubricate the window mechanism or clear out the water drains. Or if you need to change the door handle.


Locate hidden screw beneath plastic cover in the inside door handle.

door panel w123
Loosen little screw hidden behind the plastic cover

Locate the two screws inside the arm rest.

door panel removal w123
Arm rest screws

Pull put the chrome cover and find the third and last screw for the arm rest.

door panel removal w123
Drag out the chrome cover to locate the upper screw

If you are so lucky so unlucky to have a manual window regulator mechanism. You have to pull off the window regulator handle , drag the plastic cover straight upwards from its center to get it off.

door panel removal w123
Take off the window regulator handle if you have one

Remove the two screws from this door striker chrome cover.

door panel removal w123
Chrome cover

Now comes the tricky part. The front upper corner of the plastic pocket in the door has a plastic clip that sits in the door frame. To get this one off you can not pull outwards on the door! You must first loosen all of the plastic clips around the door edges, and when they all are loose you can pull UPWARDS on the door panel and the clip for the plastic pocket will loose (see image). The only thing that is attached to the car then is the upper edge door panel. Just pull more upwards and it will come off.

door panel removal w123
Pop out the panel from the edges. Then drag up on the panel and make sure the tab is loose located by the

The door has a plastic sheet over the door holes to keep moisture from deteriorating the door panel. Because rain water from the outside window runs down into the door slightly between the seals and leave from holes at the bottom of the door. The plastic cover protects moisture from destroying the door panel. The car is not a u-boat and therefore this plastic sheet needs to be there, if it is old, cut out a new one from some heavy plastic and replace. Just use some random glue to keep it in place while putting the panel back on.

door panel removed w123
Plastic prtection under door panel

As you can see here the edges of the door panel has many white plastic clips, usually some of these old ones break and they are good to have some spare ones at hand.

inner door panel w123
Door panel with plastic clips, replace if broken


How to Remove the entire rear Sub frame

If you like challenges in your life..

Whoa that sounds difficult you could think, I agree it’s not the easiest thing to do in the world. Also doing this without a lift is more tricky, since you have to lower the whole assembly instead of just lifting the car up.

When would you need to do this job?
This is quite a rear job, but changing differential or trailing arms this might be necessary. Also with restoration, body work or mayor overhaul of the car suspension such as replacing those difficult rubber bushings.


Set aside time, this is time consuming. Don’t expect to do this on a Friday and be driving again Monday morning unless you are super man. I will rank this maybe even more time consuming than taking out the engine.

Get all the necessary replacement rubber parts, such as sub frame rubber mounts, differential hanger, trailing arms rubber bushings. Rubber seats for the rear springs. New rear springs if needed?

Have at least 3 jacks available. And put your car high up on four big jack stands before starting. The jack stands need to placed in the frame of the car so you can lower the sub frame freely.

No special tools needed other than your large spanners, big sockets and long breaker bars. You will encounter 120Nm bolts here.

Removal Procedure

Step 1:
Remove exhaust system. Check out How to Remove the Exhaust system

Remove the propeller drive shaft. Check out How to Remove the Propeller Drive shaft

Take off the rear brake Calipers and the sway bar links.

Step4 Lowering the sub frame assembly:

Support the differential with a jack and make sure it can’t slide off. Support also the large sub frame arms with jacks.

jack supporting differential
Jack supporting the differential, note the other two jacks up front supporting the sub frame.
supporting subframe with jacks
Supporting sub frame with jacks, one on each side

Then you have to loosen the two big sub frame tightening bolts. Use a very long breaker bar and lots of force to loosen these bolts.

subframe tightening bolts
Loosen the two big sub frame tightening bolts, then remove the bracket

Then you can take off the sub frame mounting plates by loosening the two bolts to the body.

Next step is to loosen the differential hanger to the differential. If you are replacing this part (you should) then loosen the top four bolts, if not then loosen the two big bolts attached to the differential itself.

differential hanger
Loosen the differential hanger

Now the sub frame is free from the body. Start lowering the whole ting very slowly to release tension on the rear coil springs. Preferably there should be three persons lowering each jack at the same rate, if you are alone you must lower each corner a little bit of a time until the while thing sits on the ground. Use some block of wood to support the assembly while you withdraw the jacks.

Then drag the whole assembly out from the car. Congratulations!

Fitting procedure

Reverse of removal, however don’t forget to place the springs before raising the sub frame. The most difficult part was to align the whole sub frame so the bolts would fit exactly, this is more than a little fiddly.

Cheers, Robs out!