Noisy idle 87DT

Here comes,
I am sure there have been numerous posts on the MB noisy idle (especially prior to 1987, I assume). However, I had a hard time trying to find a brief description of fixing the noise rpoblem for my 124. It has 210 KMi, engine is in nice shape (high, uniform compresssion, no blowby, no block-heater during cold Mid-West winters). I know for a fact that the idle is way too noisy (could hear the clank-clank from 100 yards). Any suggestions? I've heard that a diesel engine with hydraulic (spelling?) lifters should be cleaned on a regular basis.
Thx.

[gsxr]

It depends what the noise is exactly. My guesses:

1- You have one or more dirty or defective hydraulic valve lifters. This noise is a "tap" that is 1/2 the engine speed, meaning one tap per 2 revolutions (compared to a rod/piston noise, which is equal to engine speed). This is VERY VERY common especially with high miles. Synthetic oil cures the noise probably 75% of the time, however it can take a few thousand miles to notice a difference. If Mobil-1 or Delvac-1 doesn't cure it, you may have one ore more collapsed lifters. They are easy to test with the valve cover off, but require some skill to replace as the cam must be removed - AND, they cost ~$25 each!

2- You may have a problem with one or more injectors, or carbon in the prechamber. Try Diesel Purge (two cans), and drive the car like you stole it for a few tanks (lead foot, lots of trips to the redline). This is a good idea regardless as it keeps the engine de-carboned.

3- This is not likely to be the cause of your complaint, but there are supposed to be two noise encapsulation shields/panels under the engine & tranny. Lazy mechanics often "forget" to reinstall them and the owners drive off not knowing they left behind $400 worth of sound panels! These not only make the engine a LOT quieter at idle (outside the car), they also keep water/dirt/crap off the engine, transmission, driveline, and front portion of the driveshaft. If yours are missing, I recommend locating a set & re-installing them.

4- If your belt tensioner shock has a worn bushing, it can sound VERY loud and obnoxious. Use a stick or something to press sideways on the shock body with the ngine running, if that is the problem, the noise goes away entirely when you press on the shock. A new shock is ~$40 (make sure you get the latest version - the previous one is a lot cheaper at ~$25) and isn't too hard to replace.

The 1987 300D/TD should be almost silent at idle when warm, almost like a gas engine. If not, SOMETHING is wrong. Trust me, I own two of these things!


Good luck,

[sixto]

Originally posted by gsxr
Use a stick or something to press sideways on the shock body with the ngine running, ...

Dave,

Can you elaborate on how to press on the tensioner shock? Is the intent to bend the shock?

Thanks,
Sixto
91 300SE
87 300SDL
83 300SD

[gsxr]

No, not to bend it, just to apply some side tension. I use my fingers but don't recommend that to others as you can chop off a couple in the fan if you slip. You just want to press on it moderately, if the bushings have failed, the pressure makes the noise go away while you press on it. Then you know the shock is bad. Not that it doesn't have damping, just the rubber end bushing fails and makes an awful rattling noise at idle!

[psfred]

Another cause of lifter rattle is the condition of the two little o-rings on the oil filter center bolt. These get hard and leak, and the lifter gallery will leak down overnight, takes some time for the lifters to pump back up once they get air in them.

A loud "clack clack clack" from out of the grille is the belt tensioner shock. Sounds like it's going to lock up at any moment.

Peter

[sixto]

Originally posted by gsxr
No, not to bend it, just to apply some side tension.

I meant apply force as if to bend it. If you say you do it with your hand I know how much force to apply to test it.

Thanks,
Sixto
91 300SE
87 300SDL
83 300SD

Thank you Dave, Thank you Fred,
Always nice to learn something from you. I have a brand new belt tensioner (less than 10 KMi), and brand new injectors, so I should be covered there. My major suspects are dirty lifters (maybe faulty?). In order to clean the lifters I assume I could use sime regular engine cleaner (the one applied to the oil). I understand that "engine cleaner" is not the correct term, please bear with me. Could you please let me know where do I look for the correct procedure of checking/replacing the faulty valve lifters. I have all the manuals. Is it there, or should I bring in the MB mechanic/use the web/etc.
Best regards.

[gsxr]

Well, first, do NOT use any "engine cleaners" that go into your oil! That's a great way to break things like piston rings or possibly cause other problems. The best "cleaner" you can use is Mobil, Amsoil, or Red Line synthetic oils. They can do amazing things, all 100% safely. I recommend Mobil-1 15W-50 (red cap), as it is available almost everywhere and is about the cheapest you can get. Delvac-1 is better but hard to find, and the Amsoil/RedLine products are expensive as well. Try that BEFORE tearing the engine apart to test lifters.

If you indeed must check the lifters (assuming the synthetic treatment doesn't work), the procedure is in the factory service manual - in the OM603 engine manual, group 5, I think. Basically you get the engine hot, remove the valve cover, and press down on each lifter that is not under pressure from the cam lobe. They should be firm and not move. If one will squish down easily, it is bad and needs replacement. You'll need to turn the engine incrementally by hand a couple times, until you get all the cam lobes on their base circle so you can test the lifters. I had about 5 of my 12 bad, and just replaced all of them - nice & quiet now! I saved the good ones as spares for my other car (which is quiet for now).


HTH,