A curious noise coming from an overhauled engine

[watson2]

Hi everybody.
My technician has just finished a complete overhaul of the engine 127.981 of my 230 SL. It was necessary for a problem with 2 crankshaft bearings.
The engine, even if broken, was silent up to 2500 rpm.  Only over this speed you could hear the tipical crankshaft noise.
I have complete confidence in my tehnician; he has a great experience and he made hundreds of MB engines of every type, old or recent, and tens of engines of this type. He represents a point of reference in Milan for cars like mine. But I see him desperate because he doesn't understand.
 
We have a little click that is not present when the engine is cold. When the engine warms up, you can hear this noise but if we loosen a little the injector nr.6 it disappears.
Please, click the following Dropbox link to hear the noise:

https://dl.dropboxusercontent.com/u/46424947/IMG_2870.avi

https://dl.dropboxusercontent.com/u/46424947/IMG_2870.MOV    (for Apple users)

It will request 10 or more seconds to be loaded
In this video we have the engine cold and the noise is 'off' but loosening the  injector nr.6 it comes 'on'.
The words of the technician :"It's not possible.... I loosen just a little and the tick appears"
The noise appears if you accelerate but in video it's more difficult to distinguish it.  At idle speed it's easier to appreciate it.
Have you ever heard a thing like this ?
I'll appreciate a lot your opinion.


P.S. I invite you to this link to see all the details of the overhaul:

http://freeforumzone.leonardo.it/d/10819589/Una-230-SL-a-3-posti/discussione.aspx/34

Please click on "Versione completa" (complete version) to see everything.
It's an amusing site of fans of  MB's old cars. On page 34 and the previous ones you will see many images. If you want to translate the text I checked that copying and pasting the text into google translate you can understand at least the sense  of the matter.  

[Shvegel]

In over 40 years of fixing cars I have never heard or seen anything like that.

The things that come to mind are a bad timing chain tensioner or the chain striking something?  Maybe a loose cam or fuel pump shaft bolt?

[watson2]

In over 40 years of fixing cars I have never heard or seen anything like that.

The things that come to mind are a bad timing chain tensioner or the chain striking something?  Maybe a loose cam or fuel pump shaft bolt?

Thank you Shvegel for your reply. My technician says the same thing. He's  becoming crazy.
The noise comes from the area of the cylinder Nr. 6 and the attention is now on its rocker arm and its pin.
These pieces are new like everything else but they are checking their fit.
We  decided to change these pieces because the pins were worn after 150.000 km and they did not allow a reliable adjustment.


From Germany arrived these ones that you can see on the left. The contact surface with the cam is wider in comparison
with the old ones. They told that the new ones were Ok.

The injection pump  is ok and it has been checked at least two times.
 
I'm sorry but maybe that in the video you cannot appreciate the frequecy of the noise.
The noise , live, seems  to be similar to rocker arms' one.
I think in a few hours , maybe on monday , we will have news and I'll let you know

[WRe]

Hi,
did you bleed the timing chain tensioner?
http://www.sl113.org/wiki/Engine/TimingChain
...WRe

[stickandrudderman]

That certainly is strange.
It's difficult to tell from the video but am I right in saying that the noise disappears when the injector pipe is backed off?
If so then you are removed the combustion pressures from that cylinder and so unloading the piston/crank.
Did the rebuilder check the small ends?

[watson2]

Hi,
did you bleed the timing chain tensioner?
http://www.sl113.org/wiki/Engine/TimingChain
...WRe

If you mean to lubricate it , I did not ask directly for this detail.  So  I'll do it , but  I think that this operation has been made.

 

[watson2]

That certainly is strange.
It's difficult to tell from the video but am I right in saying that the noise disappears when the injector pipe is backed off?
If so then you are removed the combustion pressures from that cylinder and so unloading the piston/crank.
Did the rebuilder check the small ends?

No, Stickandrudderman. I did not explain clearly. The noise is not present when the engine is cold ; in this case , as like as in the video, if you loosen the injector hose the noise appears.
But when the engine is warm the noise is present and loosening the injector hose it disappears. So the strangeness is that the same operation produces opposite effects depending on the engine temperature.

The details in the photo are part of the pieces we changed. I forgot: the chain and the timing gears are new.

The correction of the excessive backlashes in the cranckshaft 'shoulders' brought the values to the normal MB tolerances ( from 7 to 13 hundredths of a millimeter).
Before we could measure them with instruments used by bricklayers.
Please, look at this video to evaluate what i'm saying.

https://www.youtube.com/watch?v=HbMbpCNMq64

'Dopo Parma' means after  the rectification made in Parma (a nice town in the land of engines, near Modena and famous for a delicious ham) where we took the engine after the failures of the rectification workshops in Milan.
The man we met there is a 70 years old technician that is not afraid to put his hands on the engine of a Ferrari 750 Monza or a 250 GTO.
He made a great job on the whole engine.
I invite you again to give a glance to the link of my first message (pages 33 and 34)

[stickandrudderman]

I've never seen it on a petrol engine, but that test would be exactly what I would do to identify a failed injector on a Diesel engine; open the fuel line and noise disappears, close the fuel line and noise re-appears. Have you tried swapping the injector to another cylinder to see if the noise follows it?

[watson2]

I've never seen it on a petrol engine, but that test would be exactly what I would do to identify a failed injector on a Diesel engine; open the fuel line and noise disappears, close the fuel line and noise re-appears. Have you tried swapping the injector to another cylinder to see if the noise follows it?

Yes, done .   I think that my technician has swapped everything in the engine ...
He is a wonderfull person. In any other workshop probably they had already kicked off the car ....
On the contrary he takes this like a challenge against this problem and I'm sure he will not give up until he will not have found the origin. Without charging anything to me!
He says that when the noise is 'off ' then engine sounds like a violin...


@Wre :  the chain tensioner is near the cylinder nr.1 , while the noise is coming from the nr.6 , without any doubt.
The engine has been auscultated with 2 different types of stethoscope.

[watson2]

I had the opportunity to go to the workshop to hear directly this noise. It's much 'deeper'  than it looked in the video. It's not a tick tick ....
It seems the noise of parts of the engine like piston or gudgeon pin. It comes from cylinder nr.6 and it disappears cutting
the injection (loosening the hose of the injector nr.6 ) or the ignition (lifting the spark plug connector of the spark plug nr.6).
It's unbelievable.  In the next week  they will reopen the engine in search of the culprit.
I will let you know.

[bongo666shaftsburry]

I had the same exact problem. Couldn't locate barely audible soft "ticking" noise. Wasn't there when cold. Not in the newly rebuilt head. Sometimes I thought I was hearing things. But when auscultating I heard loud reverberating in some components--like the water pump--but not others and it seemed entirely random which part of the engine. Except when just listening with my ear, I kept returning to the back of the engine #5-6. Soft and deep. Removing a wire localized it to #6. I removed the oil pan and there I found "metallic paint" look to my oil, including cooper flakes, a sure sign it is a failed bearing. Unfortunately, I think you have the same issue.

Art

[bongo666shaftsburry]

By which I mean connecting rid bearing

[bongo666shaftsburry]

Rod

[watson2]

Rod

Unfortunately, I have a similar suspicion, but I can't believe it.
The engine, after the overhaul has worked less than 90 minutes. How is it possible?
To undestand why I can't believe, please read again my msg #6 and visit this link

http://freeforumzone.leonardo.it/d/10819589/Una-230-SL-a-3-posti/discussione.aspx/34

The level of accuraracy was really great, but .....

[watson2]

Things are evolving.....   Two days ago the engine produced its  noise just after the start and with a warm-up of about 1 minute the noise disappeared.
The engine was perfect for about 10 minutes.  Nor  idling neither over 2500 rpm the noise appeared.
After a short trip it produced again its noise, alternating moments in which it did at times when it did not .
A thing emerged: when the engine produces this noise it doesn't  run  'round' , it seems to be a little 'rough'. 

Now, if it was a connecting rod or a piston or a gudgeon pin this noise should be continous and not random.  So we now will investigate the injection pump and the fuel . I submit that the tank has been overhauled and 'tankerized', the fuel lines (in rubber and metal) were completely replaced.  In the bottom of the cup of the fuel filter we found a lot of fine grit probably coming from the rusty tank. Nevertheless it may be that there are still some 'mud' deposits in the circuit releasing fine sand that disturbs the injection.  In less than 500 km we were compelled to change 2 injectors.

What do you think about these new aspects of the matter?

[ja17]

Remove the oil filter and inspect between the paper to see if you have any copper metal flakes.

[watson2]

No metal flakes into the filter.
An update: now the noise every day has a new way to appear.  Cold engine : sometimes yes , sometimes nothing.
The same with warm engine. But now the noise can remain 'off' for a long time. Let's say that in 20 minutes of work the time
elapsed  without any noise is much more then the time during which the noise is audible.
And when the noise is audible may be it's loud so as at the beginning of this arcane, but may be also that it's much lower in terms  of intensity.

My technician was one of the first persons to make training on Bosch injection pumps many years ago , but anyway we asked a consultation
with other 2 Bosch experts. Many brains and many ears could obtain better results than one.
The matter is  assuming worrying aspects, but it is intriguing....

[ja17]

The "break-in period" just after major engine work is the most critical and most vulnerable period. Any mis-alignments, mis-torques, incorrect machining, incorrect parts, improper assembly, can cause failure. Dirt or contamination lurking in numerous hidden passages can dislodge and cause problems.  Watson, I wonder if a valve guide or valve seat is randomly coming loose in the cylinder head. This would cause a noise which may come and go randomly. Either one of these problems could cause a rough running situation to occur when the noise appears. If so head removal may be a much easier fix than a bottom end problem.  You may be able to take a bore scope into the cylinder and inspect the combustion chamber in the head for signs of a loose valve seat. You may also have some marks on the top of the piston.

[watson2]

Thank you ja17. We will take a bore scope and I'll let you know as soon as possible.  Meanwhile the technician is planning to reopen everything again, and see if there are signs


I take this opportunity to warn the member who sent me a private message that the system does not allow me to send my answer because strangely it tells me that cannot be found the userid with which the message was sent to me.

[watson2]

I spoke to my technician and he said that the engine was already 'borescoped'.
With a device with a view to 90° it was easy to observe every interior detail of all the cylinders.
No visible defect

Meanwhille the noise is changing : loud , not audible, clicking, like a hammer . Depends on the moment.
Probably  it is something that can move and can change position at any moment. The only pieces that can do this are the piston pins or their bushings.
If nothing changes in a few days the engine will be opened again....

[stickandrudderman]

Valves rotate as well as oscillate. A rotating valve that is not seating properly might well give symptoms that come and go but it tends to be uniform in its pattern.

[ja17]

Continuing with Stick's idea........................ A slightly bent valve stem could be causing the valve to stick open. Then the piston rises and slams it shut.

[tel76]

Watson says the engine( I assume each cylinder) has been bore scoped, if so then any damage to the piston from a valve would have left a mark and have been seen by the operator.

[Benz Dr.]

I had a car in that had a clicking noise that seemed to be louder at times than others but it was always there. Adjusting the valves really didn't change the noise. Eventually the engine swallowed a valve and smashed a piston. Turned out one of the valve keepers were worn just enough to be noisy but very hard to actually detect the problem. Common things are common but this isn't common in 230SL engines. I'm sure PJ will post a pic of the damaged piston.

  In a different note, I have a 280SL in that's making no noise at all. Seems the timing chain broke. I've never seen this before in nearly 40 years of working on these cars. The chain was tight when we set the valves and it wasn't making any noise. Odd thing is that the thrust washer that sits behind the distributor drive gear broke into several pieces. This is a fairly heavy part made from good steel and I can't figure out what made it break. I'm pretty sure that a broken piece of this washer fell into the chain causing it to break but it's still unclear as I don't have it all apart yet.
The head isn't damaged and nothing hit the pistons so it won't be too bad as far as repairs go.

I have a hunch that the drive gear that runs the tach and oil pump was probably loose and somehow this caused things to fly apart because the gears were barely in mesh when I inspected them. Clearly, someone had the engine apart but didn't get the small details covered.   

[ctaylor738]

Stick's comment triggered an old memory.  I had a '72 250C (M130 carb engine) that had a similar noise.  It would go from quiet to a barely audible tick, to a click,  and then a clack, then back to quiet.  I did some research (pre-internet) and learned that rotating valves had been a feature of Mercedes engines forever.  I concluded that I had one valve/rocker that changed clearance as the valve rotated.  I was never able to fix it.

Cheers,

CT