Nailing or other (300D Turbo 82) - PeachParts Mercedes-Benz Forum

Judge · #1 10-05-2003, 04:51 PM

I recently bought a 300D Turbo that had a nailing sound. When I bought it I thought that the sound was misadjusted valves, and that I'd be buying a car that I could fix cheaply.

I've done the valves and that got me more power, but no change in the nailing sound. I also changed filters all around.

That led me to research and this board. There is a lot of information in this board on "Nailing" generally describing it like the sound of a hammer nailing.
hammer nailing nails

In trying to find the problem, I then cracked open each of the injectors in turn, and that hardly or did not change the nailing sound, each time engine speed dropped, and idle became rough, but almost no change in the nailing sound.

I borrowed a mechanic's stethoscope, and found that the nailing sound seems to come from low down near the front of the block, right near the oil pan and the pulley the fan belt rides on.

I also notice that from underneath, the fan belt to some extent is wobblying in time with the nailing sound.

I'd like to hear some opinions on what to do next, and Is this likely to be the type of problem that destroys the engine if I keep driving it as is?

Wasuchi · #2 10-05-2003, 06:37 PM

Someone just recently had the lower pulley come loose. Might check to see that it's tight and look for the thread too, it was in the last two weeks I believe.

Wasuchi · #3 10-05-2003, 06:50 PM

SOS Need help

This is it!

psfred · #4 10-05-2003, 10:54 PM

A bad belt can make a noise astonishing like a bad rod -- it will go away when the belt is changed or the glazes section sanded.

However, a clank near the front of the engine can be a bad bearing, at worst actually spinning in the block. This would be bad news -- is it worse on acceleration or the same all the time? Same all the time would be more likely to be a bad balancer or pulley....

Peter

Judge · #5 10-06-2003, 09:41 AM

The nailing sound is a little worse under acceleration.

I'll go ahead and run the car for a couple of seconds with all the belts removed and then report back what I hear.

Judge · #6 10-06-2003, 02:09 PM

Well, I took all the belts off, and started the car up. No change in the nailing sound.

I had also listened a little more with the stethoscope, and I become less sure that I am able to localize just where the sound is coming from. But generally lower down.

I'm waiting for a diesel specialist, but non-mercedes specialist to take a look see.

Anyone want to give their thoughts on what is wrong, or what to try next??

psfred · #7 10-06-2003, 07:10 PM

Chain slap or rod knock.

Peter

kerry · #8 10-06-2003, 08:18 PM

If there is any evidence that an oil cooler line was replaced before you bought it, I'll second the view that it is a bearing problem.

#9 10-07-2003, 12:22 AM

Cracked piston, piston contacting the precombustion chamber, or (Dare I say) cracked crankshaft?

Judge · #10 10-09-2003, 04:56 PM

Well, I've certainly got a range of opinion on what the problem could be.

The diesel mechanic came by to take a look, but unfortantely I couldn't see with my own eyes how he made his diagosis.

The mechanic says that the problem is a bent intake valve on #3 piston.

I expect I will go with the mechanic, but am open to any board wisdom. Like I said, I couldn't hear the problem with a stethoscope on the valve cover, but heard the problem lower down and when I crack open the injector for # 3, the engine slows and idles rougher.

And if the diesel but non-mercedes mechanic fixes the bent valve problem, is there anything that I should be particularly aware of.

kerry · #11 10-09-2003, 05:21 PM

Count me as a skeptic on the bent intake valve on #3.

Wasuchi · #12 10-09-2003, 05:48 PM

Skeptic #2 right here.

I would think you would be getting a lot of smoke with a bent valve. Maybe a chugging sound too. I've had a bent exhaust lifter and it made a chugging sound and a nice blue cloud that smelled like oil and diesel. The mechanics I went to diagnosed it as a bad IP and one said burned piston... it was much cheaper and easier to fix than either of those. Something else would have to be pretty messed up to have a bent valve too. Keep us posted, guess you either need to go with that guy or try to get someone else to check it out. Good luck.

Where are you located? Maybe someone could point you to a good indy in your area.

Judge · #13 10-10-2003, 01:31 AM

Thanks for the advice. I added my location to my profile: San Francisco Bay Area. One local independent thought it would cost more than the car is worth to do a valve job.

At this point I'll try to arrange with the diesel mechanic who said it is a bent valve, and tell him that I will pay when the problem is fixed, rather than pay him to fix a bent valve. That way he stands by his diagnosis or doesn't.

Somehow I doubt that it is a bent valve, but then I'm not experienced enough. Here is one mone more piece of information.

When I last had the valve cover off, I noticed that where the front left valve cover bolt rises into the valve cover, the metal had been destroyed. That is, the air cleaner bracket had broken, and the air cleaner had become a small hammer vibrating against the valve cover. Eventually a small piece of the interior part of the valve cover had come loose and was missing. Maybe, that small piece of metal could have caused a bent valve?

I don't have a complete history of the car, on when the timing chain was replaced, and if anything causing damage had occured.

Thanks Board for the company in diagnosising this.

#14 10-10-2003, 01:41 AM

Cheap ways to look for a bent valve: Look under the valve cover, or take off the intake/exhaust manifolds and look in the ports. Compare it to the other valves and take it from there.

psfred · #15 10-10-2003, 09:29 PM

Sounds more like a dead chain tensioner and a badly stretched chain - they will run on the vavle cover if the oil gets low enough (don't ask how I know, but if anyone EVER claims "they didn't hear anything" when the car ran out of oil and locked up, they are lying!).

Peter