Hello

I got my authentic german valve adjustment tools today from ebay (the unimog set for 616 but people told me they will work with 617). I just need to get a metric feeler guage and I think i'm good to go. Can someone give me a quick rundown on the valve adjustment and also how to check chain stretch?

Thanks alot,

John

Here's how I adjusted valves:

1. Set up a wire to jog the engine. Connect the wire to the purple wire in the junction box on the right fender. This wire will go to the positive battery to jog the engine.
2. Take the valve cover off. Remove air filter, linkages (different length bolts!), and cruise control.
3. If necessary jog the engine until a cam lobe heal is sitting on top of a rocker. Determine whether it is intake or exhaust and adjust the valve to the specifications:
4. With both wrenches on the valve, hold the bottom wrench so it cannot turn and break loose the top nut (clockwise).
5. Turn the bottom nut counter clockwise (perhaps a half a turn).
6. Turn the top nut clockwise until feeler gauge slides between the cam lobe heel and the rocker arm. When there is a slight drag on the feeler gauge, stop and hold the top nut.
7. Turn the bottom nut counter clockwise to jam the top nut. Check the specifications as you are doing this.
8. Go back to step 2 until all are adjusted.

Have fun. Diesel oil is hard to get off your hands.

Mercedes Man gave a very good explanation of the actual adjustment of the valve. But, I personally do NOT feel comfortable jogging the engine with the starter. The engine could POSSIBLY start. Use a 27MM socket on the crankshaft bolt. It's a hassle to do this on a five cylinder because of the tight space between radiator shroud and fan, and your hands might get scraped up a bit. That's me, each to his own.

To accurately check chain stretch, you need a dial indicator and the exact procedure from the MB manual. To get an IDEA of chain stretch, you can turn the engine slowly with the 27MM socket until the mark on the cam comes near the mark on the front cam bearing stand. This mark is about 45 degrees from the top toward the drivers side. Now that the mark is coming close, SLOWLY turn the crankshaft until the camshaft mark lines up with the mark on cam bearing stand. Once the marks are aligned, look at the position of the crankshaft, which will be at TDC or a little after. If it is after, read the degrees on the crankshaft damper, and that gives an idea of the stretch. The cam marks are there close enough to put the timing chain on correctly, not accurate enough to measure exact stretch.

Good luck,

Since we are on the subject of valves, I was wondering why the valve clearances decrease on that engine. I would assume that as parts wear, the clearances would increase, which would mean that I would have to tighten the valves. On a Toyota engine, I found that I needed tighten the valves, on the Mercedes OM 617, I had to increase the clearance. Can anyone explain what's going on here?

The valves are constantly pounding into the seats millions of times and they eventually "wear" into the seats which reduces the clearanceI.E. the valve is getting closer to the cam. If the valves are not adjusted they will eventually start to leak and you will lose compression. The first symptom of this is hard cold starting.

The only explanation I have for the Toyota is that its a "rice burner".

I also agree with Larry on turning the engine with a 27MM or 1 1/16 socket wrench. Of course, having a grease pit in my garage makes that easier. I have found that 12 clicks on my ratchet will take me nicely to the next valve to be adjusted. I use 2 regular open end wrenches on my 300SDs to adjust the valves with no problems.

I don't agree with the 15,000 mile valve adjust interval though. I do it every 25,000 miles and some valves are still within the minimum clearance.

As far as the timing chain "stretch" is concerned, line up the timing marks on the camshaft and bracket. If the timing reading on the damper (balancer) are 3 degrees or less you are OK. More important is that the adjuster keeps the timing chain tight. That is easily determined by feel on the adjuster side of the chain. I chain is more than 3 degrees late you can either replace the chain or install an offset woodruf key in the cam gear and adjust the injection timing.

You should be able to find other valve adjust info using the search function.

~~~~PEH~~~~

It is true, jogging the engine could start the engine, but to avoid this you do the following:

1) ajust valves when engine is cold (this is the best time to do valve adjustment anyway;
2) jog engine very quickly...an instant at a time;
3) use a section of coat hanger wire to wire up the linkage component on the fuel injection pump....before you take the valve cover and linkage off, press the stop engine lever and you will see what you need to do on the linkage part connecting to the injection pump...this prevents fuel delivery to engine.

If you rotate the engine manually with a 27mm socket, it is much easier to access, with fan shroud in place, from under the car, although it is tougher to see the cam from there. I like the idea about counting ratchet clicks in order to know how far to go to the next cam lobe! I'll have to try that.

__________________
1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

I certainly hope we never have our valve clearance close up for the same reason that this happened on the old air cooled VW's. What would happen with them was valve stem stretch.

I don't think we have to worry about this on these engines. Those valves could actually stretch 'til they broke.

Have a great day,

I've been thinking about the valve clearance increasing on the Toyota engine and other than it being a "rice burner", it sounds like there is wear in the valve train either the cam or the followers. I seems unlikely the valves wouls get shorter since thay are under tension from the spring.The MB valve trains don't wear what with the super hard cam and the carbide inserts in the followers.

As far as counting the clicks on my ratchet to turn the engine, it is actually 3 repeatitions of 4 clicks each because there is a limited angle the ratchet can be turned. Your ratchet may be different but I think you will find a number of clicks that work by trial and error. I can't imagine trying to turn the engine from the top, even if I had to crawl under the car to the the engine. Even using my pit, its a lot of trips up and down.

~~~~PEH~~~~