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Garage => Mechanicals => Topic started by: Jan S on 09 May 2022, 10:22 AM

Title: Metallic sound from 6.9 engine front end?
Post by: Jan S on 09 May 2022, 10:22 AM
Engine is a 1977 US 6.9

I know this is a difficult one ... a verbal description of a sound. I'm giving it a try to see if this is a familiar sound to some of you.

-- The metallic sound comes from the front end of the engine
-- Only when engine is cold
-- It seems as if the sound goes through four cycles per second at 1000 rpm
-- It seems to be a combination of a scratching and rattling sound

Could it be the water pump? Since the noise disappears when warm ...?

Probably not the chain guides/tensioners?

Doesn't seem to be the alternator.

Any views/assessments is highly appreciated. A metallic sound from the engine is no good for my sleep  :'(
Title: Re: Metallic sound from 6.9 engine front end?
Post by: daantjie on 09 May 2022, 10:30 AM
As a very general guideline noises at engine speed are from the bottom end and at half engine speed from top end.
So approx 10 taps per second @ 600 rpm would be bottom end noise and 5 taps would be top end.
Would be best to try and link a clip.  Indeed noises can be a pain to pinpoint.
Try and get a mechanical stethoscope. They are pretty cheap and can help you localize the noise.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 09 May 2022, 04:31 PM
Thanks,daantjie!

I follow your logic regarding bottom end and top end. In my case it should be closer to 16 and 8 taps per second (1000 rpm).

My sound is somehow continuous, with variations like a sinus curve, approx. four cycles per second. My subjective assessment.

I will try to record it tomorrow, to see if the noise can be separated from the general engine sound.

The suspect I have in mind is the water pump. Has anyone experienced that sound? Does it vary with operating temperature?

I will read me up on the use of a stethoscope. Thanks for the tip.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 10 May 2022, 03:58 PM
Bought this stethoscope today.

The patient was in a good mood today, i.e. the noise could be heard in part as sharp ticks, but not as distinct as normally. And only for a short period.

After a few minutes the noise disappeared. I were able to check the alternator, water pump, power steering pump, exhaust valve area on both sides, front end in general e.g. where the chain and guides sits, top of valve cover.

All seems to be fine, for an untrained ear.

But I need to remeasure later when the noise is heard clearly.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: daantjie on 11 May 2022, 12:11 PM
Also listen to the SLS pump, might be coming from here.  Unless you don't have it as I think you don't have hydro suspension?
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 11 May 2022, 02:51 PM
Right, I don't have hydro suspension - it's a 450 SE but with 6.9 (a previous owner replaced the original 4.5 liter. And removed the AC and washer tank, among other things  >:(  ).

I checked again today. No noise, engine runs beautifully.

I have to wait until the noise is back. Annoying.

In the meantime ...

-- Could it be the fan clutch?
-- Could it be the crankshaft pulley?

At some point I might have to remove all the belts and let the engine run for a minute, to see if the noise disappears. Should be fine for the engine, I guess?
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 12 September 2022, 10:22 AM
The noise from the front end of the engine is till there, specially when cold. However, it varies. from day to day ... no obvious pattern.

I'm planning to take off all the belts, i.e. disconnect the water pump, alternator and the steering pump.

How long can I let the car run without the water pump? 1-2 min?

Any thoughts?

I'm trying to eliminate things.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Randys01 on 12 September 2022, 10:34 PM
 2 mins tops.....start with a cold motor.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: ptashek on 13 September 2022, 02:24 AM
Maybe a sticky valve lifter? They tend to emit clicking sounds.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 13 September 2022, 11:13 AM
Quote from: Randys01 on 12 September 2022, 10:34 PM2 mins tops.....start with a cold motor.

Thanks, I thought so. Should be sufficient.

Quote from: ptashek on 13 September 2022, 02:24 AMMaybe a sticky valve lifter? They tend to emit clicking sounds.

Thanks for the tip, but what do you mean by "sticky valve lifter"? The hydraulic valve lifter is full of oil/dirt and not moving freely? Need replacing?
Title: Re: Metallic sound from 6.9 engine front end?
Post by: raueda1 on 13 September 2022, 12:08 PM
Quote from: Jan S on 13 September 2022, 11:13 AM
Quote from: Randys01 on 12 September 2022, 10:34 PM2 mins tops.....start with a cold motor.

Thanks, I thought so. Should be sufficient.

Quote from: ptashek on 13 September 2022, 02:24 AMMaybe a sticky valve lifter? They tend to emit clicking sounds.

Thanks for the tip, but what do you mean by "sticky valve lifter"? The hydraulic valve lifter is full of oil/dirt and not moving freely? Need replacing?
Huh, I just tried to respond to this but it apparently didn't post.  Anyway, I think I have a "sticky" lifter.  Seems similar to your description but not metallic or grinding, just a gentle, intermittent tapping that quickly goes away as engine warms up (just a minute or 2) or revs a little.  I've heard the same sound in lots of engines with hydraulic lifters.  I don't think it's dirt, maybe just some wear or clearance that disappears as engine warms up? Admittedly, I haven't tried to identify which lifter or mess with tappet clearance by swapping the spacer on top of the valve (maybe a 6.9-only thing).  It's a messy, awful job.  Cheers,
Title: Re: Metallic sound from 6.9 engine front end?
Post by: ptashek on 13 September 2022, 12:58 PM
Quote from: Jan S on 13 September 2022, 11:13 AMThanks for the tip, but what do you mean by "sticky valve lifter"? The hydraulic valve lifter is full of oil/dirt and not moving freely? Need replacing?

Likely the passages have clogged up and oil is not getting into the lifter. I believe they can be cleaned, but haven't done this myself.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 13 September 2022, 04:11 PM
Thanks to both of you.

I will start by removing the belts and take it from there.

Update coming soon.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Randys01 on 13 September 2022, 10:49 PM
The very closest valve lifter is by "stethoscope standards"  a mile away from the water pump..SLS pump alternator and other rotating hardware.

So identifying a valve lifter should be relatively easy.  Listen along the inlet manifold side of the cam box for that tick.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 18 September 2022, 02:32 PM
Quote from: Randys01 on 13 September 2022, 10:49 PMThe very closest valve lifter is by "stethoscope standards"  a mile away from the water pump..SLS pump alternator and other rotating hardware.

So identifying a valve lifter should be relatively easy.  Listen along the inlet manifold side of the cam box for that tick.


Thanks for the tip!

Today I was able to compare the engine's stethoscope-sound with a smooth running 380 SEC. Alternator, power steering pump and water pump fairly similar (although a bit more noise from the power steering pump). Further tests without the belts will follow.

And a bit more ticking sound from the engine's exhaust side cylinder 2-4.

Later this week I will remove the air filter and measure at the inlet.

To be continued ....
Title: Re: Metallic sound from 6.9 engine front end?
Post by: daantjie on 18 September 2022, 02:59 PM
Ticking could also be an exhaust leak right at the manifold.  The "tick" is actually an air pulse/puff.  Usually it is worse with cold engine then as the heat makes the metal expand the sound gets less pronounced.  You can also use a length of hose and probe with one end then hold to other end of the hose to your ear. 
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 18 September 2022, 03:06 PM
Quote from: daantjie on 18 September 2022, 02:59 PMTicking could also be an exhaust leak right at the manifold.  The "tick" is actually an air pulse/puff.  Usually it is worse with cold engine then as the heat makes the metal expand the sound gets less pronounced.  You can also use a length of hose and probe with one end then hold to other end of the hose to your ear. 

Interesting, thanks for the tip! Search continues .....
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 24 September 2022, 09:08 AM
Today I took off all the belts.

Ran the engine without alternator, fan/water pump and power steering pump for 1-1.5 min.

The great news is that the engine ran smooth as a warm knife in butter  :)  Fantastic to hear!

The noise must be coming from the fan/water pump or maybe the power steering pump (the alternator moves smoothly).

Stethoscope test gives no further information ... for an untrained ear.

Any thoughts?

Replacing the water pump is a big job, I guess, and difficult to get a new/renovated pump?
The steering pump is easier to get, I assume
Title: Re: Metallic sound from 6.9 engine front end?
Post by: rumb on 24 September 2022, 01:14 PM
I believe MB sells them for a princely sum of @$1150

I understand rebuild is difficult. Some out there have done it.

old thread, someone in australia was rebuilding them
https://forum.w116.org/mechanicals/6-9-water-pump-replacement-2/msg53322/#msg53322

Here is a thread on removing the pump.
https://www.topklasse.org/forums/threads/6-9-water-pump-replacement.4636/

Here the real info:
https://forum.w116.org/mechanicals/mercedes-6-9-water-pump-overhaul/
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 24 September 2022, 04:12 PM
Thanks, Robert

I'm not seeing the pics ... are you?

I also found this great thread from 2019: https://forum.w116.org/mechanicals/mercedes-6-9-water-pump-overhaul/

My cooling temp is where it should be and stable. I don't think I have a leak in the water pump. However, the noise comes from the water pump and/or the power steering pump. Hard to say.

Search continues ...
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Randys01 on 25 September 2022, 12:33 AM
Ok  rat down which one it is......pwr stg pump is unique to 6.9 but bearing/seal kit etc are off the shelf.
As yours is not a 6.9 you could run a std pwr stg pump for ease of change over.
The water pump is another story...there are two versions...square and round. The respective pump must fit the respective base.
If the classic Centre still has water pumps BUY one!..........oh they're a nightmare!%#
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 25 September 2022, 05:23 PM
Quote from: Randys01 on 25 September 2022, 12:33 AMOk  rat down which one it is......pwr stg pump is unique to 6.9 but bearing/seal kit etc are off the shelf.
As yours is not a 6.9 you could run a std pwr stg pump for ease of change over.
The water pump is another story...there are two versions...square and round. The respective pump must fit the respective base.
If the classic Centre still has water pumps BUY one!..........oh they're a nightmare!%#

Thanks!

Yes, search continues ....

It turns out the steering pump is from a W126 380 SE (part nr. A 126 460 1480 with 82 bar) but seems to fit the 6.9 engine ... as far as I can tell. A previous owner in the US must have installed it.

I assume the steering box is from the original car, i.e. 1975 US 450 SE 4.5 liter.

Square and round water pump ... how can I see the difference? The engine is a 1977 US 6.9 if that helps.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Randys01 on 25 September 2022, 07:41 PM
The year etc won't help in determining whether it is square or round type.
This post  is not helping as I can neither send/read attach and I dont post BUT someone else will surely chime in with a picture.
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Jan S on 27 September 2022, 05:24 AM
Anyone has pics of square and round water pumps?

I'm trying to determine which one is in my car.

Title: Re: Metallic sound from 6.9 engine front end?
Post by: raueda1 on 27 September 2022, 09:25 AM
Quote from: Jan S on 27 September 2022, 05:24 AMAnyone has pics of square and round water pumps?

I'm trying to determine which one is in my car.


If you can see it at all it's pretty clear.  There are 2 aluminum pipes going down from the rear of the water pump body on the front of the block.  The pipes are either round or rectangular.  Mine are round though my impression is that rectangular is more common.  Cheers,
Title: Re: Metallic sound from 6.9 engine front end?
Post by: Randys01 on 27 September 2022, 06:41 PM
Funnily enuff I came across a couple of spare pumps in storage after 5years and as Dave has said...the square one has square-ish pipes and the round one is definitely round pipes.