I finally got around to working on my 1982 300D Turbo. It was vibrating terribly at idle and lacked power.

After a few repairs including motor mounts and throttle linkage work it is running much better. The idle is smooth but there is a pretty pronounced oscillation/rolling. It is pretty obvious. Increasing idle speed doesn't take it away and the rack damper adj bolt (new version and good) makes no effect on this oscillation.

The last time I checked (35k miles ago) the timing chain was stretched 5degrees over spec. I'm going to check it again today with a dial indicator this time and consider a woodruff key if called for. Will also look at the rails for wear. valve lash was checked about 25k miles ago and will check that out today as well.

Finally my question:
I just measured my IP timing with the drip tube method. At 23 degrees i pump the manual pump and fuel streams out. At 22 1/2 degrees it goes to a drip the rate depends how much i pump on the manual pump and at 22 degrees no more drips. So my timing is 22 1/2 degrees. Will adjusting this to 25 degrees make a big difference? Somehow i doubt it. I want to know if it would be worth advancing just assuming I don't change the valve timing w/ a woodruff key.

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1972 450SL
1982 300D Turbo

12k IIRC for valve adjustements. 22.5 is way advanced.

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The spec is 24 BTDC. 22.5 BTDC is fine. I wouldn't make the effort to move it.

Thank you Brian.

I am looking at chain stretch now. I carefully ligned up the notches on the cam. The crank shows 6 degrees ATDC. Do you think I may need to put in an offset key. I'll try measuring with a dial indicator now.
BTW I can only see the upper part of the tensioner rail and the upper guide rail. The tensioner rail is aluminum backed. The plastic cover is showing some fine cracking on the upper 1/2". Really don't want to change it unless really necessary. What do you think?

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1972 450SL
1982 300D Turbo

I cant get my dial indicatior pin on the valve spring retainer. The pin on the dial indicator is not long enough. So I guess I'll just have to believe it's stretched 6 degrees (maybe 5) based on the cam notches. Will the 2 degree at cam (4 degree change on crank) offset woodruff make a world of difference in terms of performance, mpg and preserving rails, tensioner and chain?

And what about that oscillation I get at idle?

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1972 450SL
1982 300D Turbo

If the chain is truly elongated by 6 degrees (and confirmed with the dial lift method), I'd consider a 6.5° offset key (p/n 621 991 02 67).

I'm not understanding what the "plastic cover" is...........?? If it's the surface of the tensioning rail, this material is far from anything close to plastic. It's wear characteristics are truly amazing and it still has life at 300K on most engines.

Changing that rail is a real PITA. Everything in the front of the engine has to be removed.

Brian, thanks yet again.

Yes it is the cover of the tensioning rail that i called plastic. I don't want to change it because it's too much work unless really needed.

I wish i knew how to get my dial indicator in there. The pin on the indicator is just 1" long and that's not long enough to get it down in there on the valve spring retainer. Is there somewhere else i can measure 2mm lift such as directly on one of the cam lobes? If I really have 6 degrees of stretch I guess you are suggesting to fix this and i may get a real improvement?

BTW, how much work is it to change the woodruff key? The FSM makes it look complicated. Does the tennsioner have to be relieved to pull the gear out far enough?

Engine has 220k miles. Oil changes are done properly and regularly.

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1972 450SL
1982 300D Turbo

I'd just leave it alone.

You need to set the pin on the top of the valve spring retainer. You cannot measure anything on the lobes.

You'll get an improvement. Whether you'll characterize it as a "real improvement" is unknown. It's a diesel, remember, and improvements are slight in most cases.

You do need to remove the tensioner to gain sufficient slack to remove the camshaft sprocket. If you decide to do it, pay careful attention to the washer that is directly behind the sprocket and prevent it from falling into the abyss. Also, block the camshaft from the rear as it will slide rearward without the retention from the camshaft sprocket.

I wouldn't do the Woodruff key until I was certain of the timing via the valve lift method.........even if you need to get an indicator with a longer pin.

Agreed, I'll leave it as it is.

I just checked the valve clearence on 2 intakes and 2 exhausts. They are barely on the tight side. Just 1 thousands of an inch tighter than spec on the intake and 1 or 2 thousands on the exhaust. I will continue measuring all of them. Again my question is should I bother adjusting if I'm at .003 instead of the .004 spec on intake and .012-.013 instead of the .014 spec on exhaust?

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1972 450SL
1982 300D Turbo

I wouldn't bother with it for .001" on the intake or .002" on the exhaust. But, consider that you'll need to check them again at another 6K or so because you're pushing the limits of acceptability.

In very cold temperatures, I'd adjust them to spec..........you can have problems on the intake valves with the stock specs if it gets very cold.

Actually, it has a lot in common with much of the advice offered on this forum. It's slightly retarded!!!

I found a couple of valves that were too far off so i bit the bullet and adjusted them all to spec (exh .014", int .004"). From front to back these are the lashes I measured before adjusting: .012, .003, .001, .012, .012, .002, .002, .014, .010, .003. I haven't made any other modifications so I report back if there was any performance change. Also that pesky oscillation at idle.

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1972 450SL
1982 300D Turbo

Yep, better to be safe with more clearance rather than less.

When you state "oscillation"...........are you describing "hunting" where the engine goes up in rpm and then comes back down at a frequency of about seven or eight times per minute?

No hunting, engine RPM is steady. The engine is moving with a higher frequency oscillation than you described, 2 maybe 3 cycles/sec. I replaced the motor mounts and that got rid of the shaking. Trans mount is good. Rack idle bolt (new design) adjusting does not remove the oscillation. Now there is just a rolling but rather large amplitude oscillation with the frequency of about 2.5/sec. Usually you get that with diesels if the idle is too low but that is not my case.

Otherwise the car has plenty of power (filters are relatively new), burns about 1 qt per 1500 miles and smokes a bit on hard acceleration. EGR was disabled (control hose pluged with a ball) bearing years ago.

BTW, the air filter support bracket broke in two where the the two parts that are spotted welded together form a "T". Tomorrow I will either mig weld or screws the two pieces back together again. Hopefully I can maintain 3D positioning so the air filter housing mounts back OK.

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1972 450SL
1982 300D Turbo

Try loosening one injector fuel line at a time (find the thread on trouble shooting injectors first to get more details) at idle speed. When you do this to a good injector should make the car idle worse (the RPM should drop and sound of the engine will change). If there is a bad/poor preforming injector when you loosen the line there may be little or no change in the idle speed (engine RPM).
A poorely seated engine valve can also cause the problem you describe. A compression test might find it.