Rattling noise at the front of engine - PeachParts Mercedes-Benz Forum

haromaster87 · #1 03-05-2013, 01:34 PM

Hey guys,

I've noticed a noise coming from my engine on my 1984 300D. The noise is only apparent when the car is cold, and even then it only seems to occur when the temp is kind of cold outside.

The noise sounds like a rattling. Almost like something loose smacking. Like if a bolt was backed out and a washer was smacking around on it. Haven't found any evidence of that, just a description. The noise does not go with the idle of the engine. It has no discernible pattern, but seems to be happening faster than the idle. When revved up the noise seems to subside, and when the engine warms up, the noise seems to subside as well.

It really scared me when I heard it the other day as my mind immediately jumped to rod bearings and things of the sort.

None the less I pulled it in while it was still cold to check it out. My girlfriend is a nurse and gave me an actual stethoscope to use, so I was able to listen to specific components. The first spot I put it on was the front of the block. I could hear the engine turning over, but the rattling was not coming through.

I got under the card and put it on a few different spots on the oil pan and still did not hear it. I also placed it on a couple of spots on the block, but there was no rattling/knocking in my ears. With how much this noise resonates throughout the engine bay, I think it would've definitely made it into the stethoscope had it been bottom end component issues.

So I started listening around various front engine components. This was prior to me researching the issue. I listed to the vacuum pump. It was noisy, but it was a constant, steady noise. I did not hear the rattle coming through the vacuum pump. However, I've read that this component can fail and cause this noise, so I don't know if maybe it is failing and the noise didn't make it into the Stethoscope?

I listened into the various other belt components and didn't hear much. But every time I just listened with my ears, it sounded like it was coming from the center of the front engine bay.

I put the stethoscope up to the water pump and swear I could hear a trace of the noise. The most I had heard from all the components.

EDIT: I did also listen to various points on the valve cover, but did not hear anything major from there.

So after researching, I've read this kind of noise is commonly found to be the fan clutch, vacuum pump or a timing chain guide.

Based on what I said about the noise I heard in the vac pump. does that likely rule it out, or could the noise just not be resonating through the case and thus not into the stethoscope?

And how could I test the fan clutch? Now that I read about the tensioner, I'm going to do some more in depth listening in that area tonight, but I'd love to have a couple other test I can try to hopefully narrow this down.

Thanks guys!

bd1308 · #2 03-05-2013, 01:39 PM

You'd be amazed at how much racket a dis-connected "non-working" A/C compressor is, if you have a disconnected non-working one. Those little pistons doing nothing but clanking around on that wobble shaft sounds a little ominous.

haromaster87 · #3 03-05-2013, 01:44 PM

Quote:

Originally Posted by bd1308

You'd be amazed at how much racket a dis-connected "non-working" A/C compressor is, if you have a disconnected non-working one. Those little pistons doing nothing but clanking around on that wobble shaft sounds a little ominous.

Really? That would make sense and be excellent. I do have an AC compressor that does not work and is still connected via belt to the engine. Come to think of it, I never listened to it either. That would be too good seeing as I could disconnect the belt and just replace the compressor if I ever get around to fixin the AC on this thing. haha

pawoSD · #4 03-05-2013, 01:46 PM

A continuous can-banging rattling can be a failing water pump on the 617 engines. I've seen it twice so far.

bd1308 · #5 03-05-2013, 01:47 PM

Yeah, it did make some "small screw rattling around a tiny metal box" kinda sound...plus I guess if the bearings are shot it'd make some "live squirrel trapped in a cage" kinda sound.

FWIW, I never have trapped a squirrel in a box. Just using a wild imagination waiting for databases at work to get rolled back.

Brian Carlton · #6 03-05-2013, 01:52 PM

Quote:

Originally Posted by haromaster87

I listened into the various other belt components and didn't hear much. But every time I just listened with my ears, it sounded like it was coming from the center of the front engine bay.

1) See if the sound is emanating from the valve cover..............

2) See if the damper on the crankshaft is intact. Watch the damper at idle and look for a wobble of the damper.

The a/c compressor is unlikely unless the clutch is frozen. If so, the noise would never disappear.

haromaster87 · #7 03-05-2013, 02:00 PM

Quote:

Originally Posted by pawoSD

A continuous can-banging rattling can be a failing water pump on the 617 engines. I've seen it twice so far.

Can-banging rattling. That sounds a lot like what I'm hearing. I'll have to inspect the water pump closer.

Quote:

Originally Posted by bd1308

Yeah, it did make some "small screw rattling around a tiny metal box" kinda sound...plus I guess if the bearings are shot it'd make some "live squirrel trapped in a cage" kinda sound.

FWIW, I never have trapped a squirrel in a box. Just using a wild imagination waiting for databases at work to get rolled back.

Haha, another good description of the noise!

Quote:

Originally Posted by Brian Carlton

1) See if the sound is emanating from the valve cover..............

2) See if the damper on the crankshaft is intact. Watch the damper at idle and look for a wobble of the damper.

The a/c compressor is unlikely unless the clutch is frozen. If so, the noise would never disappear.

I meant to put in the original post, I did check the valve cover. On the front and over the various cylinders. Did not hear the specific rattle coming from there.

I will be checking that damper. I read about those making a noise like this and the hell that can break loose if it lets go.

Thanks for all the tips so far guys!

vstech · #8 03-05-2013, 02:05 PM

if this is on the 84 300D in your signature, it's not a belt tensioner, you don't have one...

haromaster87 · #9 03-05-2013, 02:09 PM

Quote:

Originally Posted by vstech

if this is on the 84 300D in your signature, it's not a belt tensioner, you don't have one...

Oh, you're right. My mistake. Looks like I the thread I read said it's a timing chain guide, not a tensioner. I will update that.

Orv · #10 03-06-2013, 03:01 AM

I've had surprisingly loud rattles from the adjustment bolt on the alternator being loose. I had snugged up the bolts to lock it in place, but had neglected to give the adjuster a couple turns to snug it up tight.

Another one: Where the downpipe comes down from the engine, it goes through a U-bolt that holds it to a mount, right after it curves to head along the length of the car. If that U bolt is loose you'll have a clanking rattle.

Stugist · #11 03-06-2013, 03:35 AM

Check the alternator. There's a bolt or two that, if loose, can hit against the flywheel. That would cause a small rattling like that.

turbobenz · #12 03-06-2013, 04:46 AM

its common to find a circlip and or a piece of spring in the oil pan on 617 turbos with high mileage. The circlip that holds the spring for the oil pump chain grinds through the pin with time, popping off. The pin then can supposedly begin walking out until it starts contacting the oil pump gear or something.Ive seen three high mileage 617's, including mine, that have had the circlip pop loose.

Orv · #13 03-06-2013, 10:24 PM

Quote:

Originally Posted by Stugist

Check the alternator. There's a bolt or two that, if loose, can hit against the flywheel. That would cause a small rattling like that.

I think you mean the harmonic balancer, but yeah, there's actually a number of accessory bracket bolts that can hit either that or the water pump pulley if they back out.

cho · #14 03-07-2013, 04:51 AM

Quote:

Originally Posted by Orv

Another one: Where the downpipe comes down from the engine, it goes through a U-bolt that holds it to a mount, right after it curves to head along the length of the car. If that U bolt is loose you'll have a clanking rattle.

yes,this one is strange,no rubber (at least on mine,I guess the temp is issue...) to soften the vibes,..
if loose,... cacophony

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