How to adjust the valves in the M110 engine – Part 1.5

Part 1.5 of valve adjustment of Mercedes M110 Engine. Stuck valve adjusting nuts require a DOHC valve compressor tool, which is hard to obtain for this engine.

Christmas came early..

Notice the part 1.5 nonsense, what is that all about you might think to yourself? Have I gotten mad over New Year’s? It’s rather just because of the half usefulness of this article. Since you readers are mostly DIY mechanics and Mercedes enthusiasts, I want to convey a story of the journey toward valve adjustments of such an old engine. In this way we share the ups and downs, the challenges and successes, and maybe learn something on the way.

Remember in Part 1 where I ended with 4 different options listed with increasing price and pain? Well since Christmas came early (2018) I ended up somewhere with a solution in the middle of option 1 and 2. After trawling the used car tool market, mostly ebay, I managed to find a seller which sold a late 70s vintage Mercedes valve compressor kit for DOHC engines. Although not specific to the M110 engine it is close enough, that with a few modifications it might just work. Let me just say it was the most expensive vintage tool I have ever bought. Lets hope it can come to good use!

Mercedes late 70s DOHC valve spring compressor tool.
Mercedes late 70s DOHC Valve spring compressor tool for several engine models.
M110 DOHC valve compressor tool
This is the M110 engine specific tool which is out of production. Looks similar right? Although not the same, I’m sure we can adjust the obtained one to do the same job with some modifications.

I almost did not buy due to the high asking bidding price, but after the deadline was reached it was still for sale. I decided to go for it as a Christmas present for myself and bid on the tool for a little less. Chance happened that we compromised and reached a fast deal. Two weeks before Christmas it landed in the mail box.

Valve spring compressors
It came with 4 different valve compressors. I might use the second from the left with some modifications.

It comes with 4 different valve compressors, although I’m not sure if any of them fit right out of the box. I might need to adjust one of them. The lever bar has a simple screw on attachment to swap out the compressor ends. The Hook is not attached, but can be placed in different grooves. I might also need to adjust the arrangement here as well.

Under I have tried to visualize how the tool is operated on the valve head. The idea is to compress the valve just enough so I can slide off the rocker arm. Since the valve clearance adjusting nuts are so tight we need a socket over the nut which is naturally blocked by the rocker arm.

I tried to overlay this tool over the valve and camshaft arrangement in the M110 engine. Here The sizes are not 1:1 but illustrates the point. Already here we can see that there might be clearance issues between the engine wall and the compressor. Also the circular edge for the compressor surface has to be cut, so it can slide onto the valve top under the rocker arm.

I’m excited to see how the tool can be used in real life, but since it’s winter and the car is hidden away, this have to wait until spring. I’ll keep you posted on the progress in this journey as soon as possible.

Cheers! Robs out

Other news: I tried to sell the S600 in the autumn, but was unfortunately little interest which is hard to believe when regarding the current economics and huge interest in classic cars. Norway is a weird country.. The car is in mint condition with low mileage so I will not give it away for free. I will instead keep it and enjoy it, make some good articles about the w140 and let time mature it into a true classic.

How to adjust the valves in the M110 engine – PART 1

M110 Engine Valve adjustment – Part 1

I planned the valve adjustment job to be straightforward and easy, making it a delight to write an article about afterwards, but no! In the end I could not even adjust a single valve out of the 12 in total, and this is why I will divide the so called adventure into multiple parts and share my experience on the topic.

“Mother nature beats father engineer every time..”

Valve adjustments should be done every 15.000 km which means for most people every 2. or 3. year and is important for engine performance and fuel consumption. Neglected maintenance can even end up wearing your cam lobes prematurely if they get too tight!

A story of success

I got all the parts I needed, that is really only a valve cover gasket set. I let the car stay overnight for the engine to cool down. Then I start pulling out the spark plug wires, no need to mark them with cylinder number..haha! I unbolt the valve cover in a breeze, the nuts I throw somewhere neat.

Then I check the valve lobe timing, oh see that the first one is perfectly aligned already so I can start adjusting the first valve immediately. I find my valve feeler gauge easily from the toolbox and it’s not rusted together at all. I adjust the first valve and since my memory is faultless I can easily keep track of all the valves I have adjusted and the ones who are left. The crank is so easy to turn by hand and I don’t need to remove the radiator shroud or anything silly like that. I get everything done in under a less hour and bolt everything together with the new valve valve gasket and I’m now already on my way to the race track with 40 more HP.

A cake, but it's a lie

This is all however a big lie.

Sometimes wisdom words are painfully true: “Mother nature beats father engineer every time..”. The real struggle you can follow below.

bleak Reality

So before starting you should take care of a few things. In theory a valve adjustment is easy and requires little preparation and engine know how. You need a new valve cover replacement kit, since your old one is probably leaking oil and a new one is very cheap. The valve adjustment can be made either when the engine is warm (just after driving) or cold (20°C). I really recommend the latter since you will not burn your fingers and get better results since the engine is not cooling down slowly. Ideally it should be at ambient summer temperatures in the shade. You have to leave the car overnight to properly cool down after driving so this have to be planned in advance.

The tools you need is just really a spanner and some feeler gauges for the adjustment and a socket for turning the crank over, but as we will see here this is not the case for my case.

M110 engine with air filter off
Marked spark plug wires.

I start by removing the air filter housing to access the valve cover freely. Then I mark every spark plug wire with a number on a piece of tape. Usually the spark plug wires are different length, but it’s so much easier to plug them in afterwards. Then I take out the spark plugs.

Now I can start removing the valve cover bolts and place them somewhere safe. I note that the middle ones have a copper shim which I can keep, but the new valve cover gasket comes with replacement ones. It’s always nice to keep bolts, nuts and shims if they are in good order.

M110 engine with valve cover open

With the valve cover off is is extremely important to not drop anything into the engine like a nut or something, since this will cause catastrophic engine failure. Also keep dirt away and exercise hospital  level cleanliness while the engine is open. Cover it always when not working on it, like lunch break etc..

I then go in the the toolbox to find my gauge feeler blades and realize they have rusted together and end up throwing them. I go in my dad’s old toolbox and luckily find some that are in a bit better shape. With a cold engine the inlet valve clearing should be 0.10 mm and the exhaust 0.25 mm. I draw a diagram over the valves so I can mark them after every adjustment, it will be very hard to keep track of otherwise. Just try remembering 12 boolean positions for reference!

Valve gauge feeler tool

Of course none of the valve lobes are pointing  directly vertical for any of the valves after opening the cover, that would be too easy! So I go ahead and try to turn the crank, but come over a problem. The fan shroud is too tight to engine for me to get any socket tool and ratchet to the crank. Loosening just the fan shroud is not helping either since the fan is sitting tight to the shroud. Then I loosen the fan and I can just get enough room for the ratchet and finally being able to turn the crank.

I align the first cam lobe and is ready to check the valve clearing. I expect most of the valves to be to bee way too tight, and the first one is as expected. I grab my spanner to start adjusting, but the valve adjusting nut is not moving at all. In fact I’m starting to slightly round off the nut. I stop before I ruin it. Then I quickly check a few other valves, they are all tight as expected, but also here the valve adjusting nuts are super tight. I am totally stuck.

After searching the Internet for similar issues it seems this is a common scenario for these aging engines. The nut material is quite soft and can easily be rounded off when they are tight. The solution is to remove the rocker arms to access the whole nut so you can get a socket over it to exert more force.

Seems easy right? To remove the rocker arm you need to depress the valves somehow. They are under very high pressure from the valve springs and a special compressor tool is needed. There are many different DOHC valve spring compressor tools on the market, however the M110 engine have very tight space between the cams and the engine walls where the spring compressor have to fit.  And the valve is at an angle so the tool need to be just for this purpose. There is such a speciality tool for the M110 engine, but I can’t find it on a single place on the internet.  It turns out it is in fact out of production. Fuck!

I am stuck and have to abandon my job and put everything back together. This was a waste of time! (But in the back of my cynical mind I think it can be turned into an article at some point..)

Here is a diagram over the valve assembly to illustrate the point better.

Valve Configuration M110 engine

The valve compressor tool is like a leverage bar with a hook for the cam axle and a crow foot depressor at an angle that can slide between the engine wall and the cam axle down on the top of the  valve. It looks like this:

M110 DOHC valve compressor tool

how to solve the tool problem

I have considered some options below and ranked them from easier/cheaper towards more expensive options.

  • Obtain the tool

I have really tried to find this on the internet, but with no success. I think I will not be able to obtain it. Not sure if Mercedes has one , but I am scared of even asking, it’s probably super expensive.

  • Make the tool myself

I know how it looks like and roughly the sizes. I can easily obtain some steel, and a crow foot. I have a welder so I can make the tool. However I expect it to take some time to assemble. Definitely worth looking into.

  • Take the car it to a workshop

I can just take it to a workshop and tell them to adjust the valves, but they are going to run into the same problems like me and they might end up ruining the valve nuts unless I explicitly tell them the problem in great detail. Remember these days no cars require manual valve adjustment and only the more experienced mechanics have done this. If you want things done right, better do it yourself.

  • Contact Mercedes on how the fuck….

This is my last option and will consist of asking if they have such a tool, and if the tool is not for sale (or out of production), if they can at least adjust the valves if they can send a tool from Mercedes Classic in Germany to their workshop. Problem is that is going to be very expensive for a simple job. Not likely I will venture down this path. Also would turn into a dreadfully boring article for you DIY people!

More on this adventure when we return in Part 2 of the valve adjustment nightmare… soonish

(Not really, it’s damn winter and car is parked)

Cheers, Robs out!

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. The top one is the adjusting nut and the lower is the tightening nut, quite counter intuitive! Use the valve adjusting wrenches to adjust the valves by loosening the bottom nut and the actual adjusting is done with the upper nut while keeping the lower nut still. In an old engine they might have become very hard, so it’s very important to have the proper tools with super tight clearances otherwise you might ruin the nuts. Turn the upper 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 so just be patient and try a few times until it gets right. 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 you are alone, you have to always recheck your own work with the feeler after tightening and it takes a couple attempts to get it right.

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 rubber 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 too tight before the adjustment and is a indication of neglected valve adjustment maintenance.