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  #1  
Old 01-11-2009, 08:28 PM
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Squeaky Timing Chain

I ran into a strange situation yesterday while doing a valve adjustment on my
'83 240D. Halfway through the procedure, which I have done many times, I
noticed a very audible "springy" squeak when I manually turn the engine as in
rotating a cam lobe to the right position. It first occurred after I had left
it for a while about halfway through the job and had come back to it later.
I'm sure I did not hear it until then and I believe it is loud enough such
that I would have heard it the last time the engine was running the day before I removed the valve cover to start the job.

A check of timing chain stretch at the start of the routine showed ~4
degrees. I'm not aware of anything falling into the timing chain recess, no
nuts, washers, or other parts are missing, and as far as I can see into the
recess with a bright light I can see no foreign items. I thought perhaps it
was coming from one of the peripheral items in the belt system, e.g.
alternator, etc. but the sound appears to be emanating from the chain recess
or the cam area. It is consistent with each rotational movement of the engine crank/chain.

I thought perhaps it was due to lack of oil on some surfaces due to drain
down, but that should be somewhat typical as any shut down period. At this
point, I'm a bit reluctant to button it up and fire it up. Has anyone had a
similar experience or any suggestions? One thought is that it could be vacuum pump noise, but it certainly seems strange that it would first occur halfway through a valve adjustment.

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Old 01-11-2009, 08:52 PM
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I vote the vac pump. can you use a stethoscope or stick to listen to it and narrow down the location?
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  #3  
Old 01-11-2009, 09:52 PM
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how many degrees of movement @ the crank cause the noise?

@ which degrees on the crank does this occur?

how are you turning the crankshaft?

definitely inspect Vacuum pump as suggested.
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Old 01-13-2009, 01:23 PM
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Squeaky Timing Chain

Quote:
Originally Posted by jt20 View Post
how many degrees of movement @ the crank cause the noise?
@ which degrees on the crank does this occur?
how are you turning the crankshaft?
definitely inspect Vacuum pump as suggested.

The noise occurs with any degree of movement and any rotational position, whether turning the crankshaft via the crankshaft bolt or via the belt system (turning of PS pump). I suspected the Vac pump, but it was very strange to have occurred halfway through a valve adjustment.
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Old 01-13-2009, 01:31 PM
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Thats not the chain or vac pump. That squeak is air being compressed in one or more cylinders on its compression stroke, the air slowly escapes around the rings (due to such a slow movement) and makes a squeaking sound.

Its 100% normal!
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'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
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  #6  
Old 01-13-2009, 01:31 PM
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Squeaky Timing Chain

Quote:
Originally Posted by mobetta View Post
I vote the vac pump. can you use a stethoscope or stick to listen to it and narrow down the location?
I'll try to find a way to isolate the noise. With 240K on the odometer, I had replacing the original vac pump on a list of upcoming things to do from just a preventive standpoint although it has never made noise and delivers a costant 22". I have heard tales of catastrophic results from vac pump bearing failures, i.e. timing chain, etc. What has been your experience in that regard? I measured timing chain stretch as ~4 degrees before starting the valve adjust.
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Old 01-13-2009, 01:33 PM
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We posted at the same time....see my post above....
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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)
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  #8  
Old 01-13-2009, 08:57 PM
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Quote:
Originally Posted by pawoSD View Post
Thats not the chain or vac pump. That squeak is air being compressed in one or more cylinders on its compression stroke, the air slowly escapes around the rings (due to such a slow movement) and makes a squeaking sound.

Its 100% normal!
Thanks for the response, and I'd sure like to think you are right about that. It's just strange that I have never heard it in the many times I have done the procedure and this time only when I was halfway through. And it sure sounds mechanical and from the chain area. But no doubt I will learn something one way or the other when I button it up and fire it up in the next couple of days!
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Old 01-13-2009, 11:40 PM
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That whistling noise should be discernible from squeaking / scraping to someone who has done the valve lash on numerous occasions.

I still do not understand the nature of this sound, but if I was able to repeat a mechanically based anomaly with EACH movement of the crank...

I would certainly not be running the engine until I had inspected the critical moving parts that may be related.

Don't forget, Vacuum pump lobes: 2
ratio of rotation to crank: 1:2
sound of your diesel squeaking its last squeak: pricey
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Old 01-14-2009, 10:44 PM
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Quote:
Originally Posted by jt20 View Post
That whistling noise should be discernible from squeaking / scraping to someone who has done the valve lash on numerous occasions.

I still do not understand the nature of this sound, but if I was able to repeat a mechanically based anomaly with EACH movement of the crank...

I would certainly not be running the engine until I had inspected the critical moving parts that may be related.

Don't forget, Vacuum pump lobes: 2
ratio of rotation to crank: 1:2
sound of your diesel squeaking its last squeak: pricey
Thanks for the input and 10-4 on the potential priciness of final squeaks. I never described it as whistling, just springy/squeaky. Today I removed the alt/fan belt to remove the water pump from the possibles and the squeak persisted. I turned the engine over with the starter and the squeak was constant. It's due for a preventive vac pump replacement so I will do that next and check it after that. With no improvement, I would then suspect TC track or tensioner.
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  #11  
Old 01-15-2009, 11:49 AM
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i think the tensioner is also a good assumption - whether the rail in the cavity, or a broken spring in the tensioner itself.

good thinking.

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