An update on the Mercedes W123. Mine is a a petrol 2.0L the so called M102 engine. This was the latest development that went into the W123. Generally this engine is considered to be one of the best. It went on into the W124 as well. Slightly modified. It got hydraulically adjusting valves. And importantly, Mercedes replaced the simplex timing chain for a more robust duplex timing chain.
Remarkably, nobody knows exactly when to change out a simplex timing chain on a M102 engine. There is nothing written on the interval in the official MB workshop manuals. You can try to measure the wear indirectly. Checking the timing marks on the valve train versus the crankshaft. But the general consensus amongst specialists tend to be every 100.000 km. I don’t know if mine was replaced at 100.000km. My car has done some 175.000 km or there about. So I felt it was high time to change it.
When we lived in our last village, one of our neighbours was extremely knowledgable on Alfa’s and Mercedes. He had been the chief mechanic at the local Alfa Romeo dealer in the Hague, then became chief mechanic at Mercedes in the Hague. He got some health problems and the last couple of years he took care of the delivery of new MB cars. Some new owners like a very detailled explanation on every feature/button/setting of their new car. And Aad was extremely good at it. He knew everything and could talk for hours. He often came out and helped me if I was busy working on one of my cars.
One night he came round and he had several bags full of parts and documentation. He had been clearing out his loft. He gave me all his old workshop manuals, and a lot of various parts. A few months ago, I learned that, sadly, he passed away.
I was thinking of him when reading up on replacing the timing chain. The (German) manual I got from him. He had gotten it from Mercedes during a training in Stuttgart. You can still see some of his notes written across some of the images.
These sort of engines, from a design point of view are some forty years old. Mine was produced in 1982. As engines go, this is all pretty basic. Also, the 2.0l version was the smallest engine option on the W123. Which also means that, by and large, everything is very accessible. You put the 6 cylinder 2.8L in and it gets very cramped.
This diagram shows the basic lay out of the timing chain arrangement
Most experts will tell you to also change out the tensioner at the same time as the chain.
Before we can get to the chain some bits have to come off, obviously. So here goes, this is how it starts. With the hood in its 90o open position. I have put tie-wraps on both hinges to keep it in place! Don’t want it crashing down on me.
First take off the cover of the air inlet filter. Three nuts and 6 clips.
The filter was still pretty clean, I can use that again
Take the filter out:
Remove the air inlet body. Couple of nuts and off it comes. Now we have access to the valve cover
Next the spark plugs come out. The reason is that with them removed it will be much easier to turn the engine. I make it a habit to always label the spark plug cables. You think that based on length you will put them back correctly and usually that works out ok. But once I worked on my Jeep Cherokee (6 cylinder) and I managed to swap two cables by accidents. The engine still started, but was running rough. I had been doing a whole bunch of different jobs, so at first I did not suspect the cables. Took me a while to figure it out. Since then, I label all cables, no matter how simple and straight forward the arrangement might look.
The spark plugs on this engine sit pretty deep. So first I blow some air around it to clean out these spark plug recess holes. Next, you need to have the correct spark plug tool.
All the plugs removed and all cables are out of the way
Here you have a view of how deep these spark plugs sit:
Valve cover removed. Just 5 nuts. It came off real easy. Sometimes these covers really stick. In which case you might have to tap them very gently with a mallet.
Inside of the valve cover. A bit mucky, they usually are.
I checked the plugs. They looked fine, these are iridium plugs by the looks of it. Even so, just checked the gap to make sure. Special little tool for that!
To get the tensioner out the alternator needs to be loosened up. Now, take it from me, on most cars that can be quite a bear of a job. Typically these bolts are very very tight. I always spray some of this special WD40 on it. This is not the regular WD40, but this one specifically penetrates and loosens up rusty old bolts and nuts. It works really well, much better than the general WD40.
Most alternators have a very similar set up. There is usually one bolt on which it swivels and one bolt that moves across a support and you use to tighten the V-belt. This latter bolt on the mercedes is very clever. It comes with teeth that interlock with teeth on the support. So by turning this bolt you actually move it forward/backward tensioning/slacking the V-belt tension. Very simple, very clever.
Even with my special penetration spray it took a lot of muscle and a large ratchet to get the bolts undone.
Here you see the alternator swung out of the way. The very large nut, just underneath the light is the retainer nut of the tensioner.
The retainer nut of the tensioner came off without too much problems too. But then I hit a snag. In order to get the actual tensioner out of the engine you need a Allen key size 17. I have up to size 13 and one size 19, but not 17mm. Quick bicycle ride to my local car part store. They did not have it either, but ordered it and it will arrive later this week.
As I had the valve cover off, I decided to check the valve clearance.
On this engine you can do that whilst the engine is still warm. They provide valve gap measurements for both cold and warm engines. Warm is anything above 50o. Again, this really shows how well the Mercedes engineers thought this through. When a car comes into the workshop for a service it’s engine might take several hours to cool down. Irrespective, here you can adjust the valves immediately or at the end of the day. You just use the appropriate measurements.
Adjusting valves on this engine is as basic as it gets. You check with a feeler gauge the gap. As explained earlier, with the plugs out, the engine turns really easy. you need to make sure that the valve you are checking is fully closed. Check the gap with the feeler gauge. It should just fit. Adding 0.05mm should make it stick. It is a very simple arrangements, a locking nut and a simple adjustment bolt. All you need is a ring spanner and a screw driver that fits really well into the adjustment bolt.
I only had to adjust one inlet and one outlet valve, off by 0.05mm. I did mention a problem with one of the adjustment bolts earlier. Last time I check the valve clearance the number 4 inlet valve had a problem. It was really a bit loose and the adjustment bolt was stuck. I was actually prepared to take the rocker arm out. But with my fancy Wd40 spray, a bit of patience and a large plier I managed to get it loosened up again.
So, all valves are fine. I will get my tensioner Allen key in a few days. Next week spanner mater Peter is giving me a hand with changing out the chain. It is a two man, four hands job.
Jeroen