Five years ago, I purchased a 1989 420SEL, my first Mercedes. At that time I purchased a full set of Mercedes manuals and started looking at the Mercedes Owners groups web sites for problem areas. My attention was zeroed into timing chains and what happens when they break; there were horror stories. I decided that I would not chance a break. I ordered the chain, got a friend to help me, and installed it in my V8. Before installation, I carefully measured the length of the new chain. My replacement procedure was to remove both valve covers in order to expose the cam shaft drive gears at the front of the engine. I then used a Dremel tool grinder to remove a pin in the chain linkage, attached the new chain to the end of the old chain, and turned the engine with a wrench to the crank shaft pulley nut, and wound the new chain right in and then bound the ends of the new chain with a link. I also replace all guides available to me from the top of the engine.

Now, was it necessary? The car had 150,000 miles on it when I did the work. After removal of the old chain, I carefully measured its length and compared it to the new chain length. I found no difference in length which meant little or no wear.

Following all this effort, further study concluded that the chain problem in the 420SEL existed only in the early models which had only a single wide chain, while the later models, such as mine, had a double wide chain which gave no problem.

I hope that this may be of value to you.

BigCar