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  #1  
Old 11-01-2000, 09:41 PM
CJ CJ is offline
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I have posted this situation several times, but I can not get an answer. I find it hard to believe that I am the only one that has ever had this problem.
Here goes:
My 1991 300D 2.5 has a loud nailing sound only at idle. It has new injectors, timing set electronically, the head was off to measure piston clearance/the rods are not bent & lots of other minor things checked.
When I first start the car in the morning, it is very quiet (quiet for a diesel anyway). Once I hit the gas and then let up so that the car idles again, that is when the nailing starts. The nailing is loud only at idle. While I am driving, it is pretty quiet. The only thing that the four big local MBZ mechanics can tell me is the following:
1. It is definately fuel related.
2. It is nothing to be concerned about or an indicator of a larger problem.
3. Deal with it, the car is fine.
I find it hard to believe that after $1,000 of work NOBODY can seem to figure this out and I am the only person on this board that has ever encountered this.
Any input would be greatly appreciated.
Thanks again for ALL of your help!!!!
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  #2  
Old 11-01-2000, 10:34 PM
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Location: Youngstown, OH
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CJ,
I don't even know if this will help but, I had a similar sound in my 91 300E. It turned out to be the dampening shock on the fan belt tensioner. I used an automotive stethascope and just started touching everything under the hood untill I found the noise. I was able to confirm that it was the dampener (it looks like a 6 inch shock absorber) by pushing on the tensioner; this quieted the sound. Be carefull around the belts.

intruder

------------------
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  #3  
Old 11-01-2000, 10:57 PM
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Intruder,
Thanks for the quick response. I am familiar with what you are describing, but my noise is "diesel nailing".
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  #4  
Old 11-02-2000, 01:49 AM
Leon Hernandez
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Don't know if this is of any value but here is a link. http://www.turbodieselregister.com/ http://www.dieselservices.com/performance/

These guys may have encountered something similiar in other vehicles. Though not necessarily in MBs. Best regards, LH
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  #5  
Old 11-02-2000, 08:43 AM
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I haven't had time to follow the above link but I will tell of my experiences here.

I have seen this a number of times and have discussed it more than once with other shops. Figuring you don't have a compression, timing, or injector problem, let me give you a theory. The quantity of fuel delivered is the quantity of fuel pushed by each individual piston stroke into the fuel line. The fuel in the line being non-compressable pushes the same quantity out the injectors. There may be numerous strokes between the time any one parcel of fuel enters the line and when it finally comes out the injector. The column of fuel thus must stay in the line.

In between strokes the fuel stays motionless in the line, checked at each end; one end by the injector the other by the pump element check valves. These valves are sealed internally by some brass o-rings. The leakage of fuel either through the check valves or the brass seals reduces the fuel in the line and affects the delivered amount.

Now for the history. I have, and at least two other techs have, changed the sound of this nailing, by retorquing the fitting at the base of the line. I have made the hypothesis above. It is also based on many idling problem repairs in all MB diesels by replacing these seals. The noise level in the 602/603 motors is only a hypothesis.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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  #6  
Old 11-02-2000, 06:47 PM
CJ CJ is offline
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Steve,
Thank you for the first logical explanation that ANYONE has given me. I spoke to my mechanics and they were very impressed.
How hard is it to replace the washers/valves for a DYIER? Specifically what do I have to retorque to correct the problem, is it where the fuel lines go into the rack?
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  #7  
Old 11-02-2000, 10:07 PM
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Steve,

You anwsered my question which had puzzled me for long time. Thank you very much. I was told that when I replace the rubber O-ring and the brass washer of the delivery valve, if it becomes noise, I should retorque it. I did not know why I had to retorque it until now.

I really cannot say enough how much I appreciate the time you spent on helping others.

David

[This message has been edited by be459 (edited 11-02-2000).]
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  #8  
Old 11-02-2000, 10:14 PM
CJ CJ is offline
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BE459,
I hate to sound ignorant, but what exactly is being retorqued and where do those little washers go? Are we talking about the fuel piping goes into the pump?
Any help or specific details would greatly be appreciated.
Thanks in advance.
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  #9  
Old 11-03-2000, 12:50 AM
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CJ,

Without a picture, I am not sure I can say it clearly but I will try. For the 602 engine, there are five small pipes on top of the fuel injection pump. One end of the pipe screws into the pump and the other end connects to the high pressure fuel line going toward the injector. Inside each of the five small pipes is a delivery valve. There is a metal washer at the bottom end of the small pipe laying flat inside the hole where the pipe screws in. Also, there is a rubber O-ring around the pipe near the bottom end of the pipe.

The small pipe needs to be torqued in a specifc way as called for by Bosch when it is screwing into the fuel injection pump. If you follow correct instructions to install the pipe and it makes unusual noise, I was told to retorque it again.

To retorque the pipe, you need a special 32-point socket. IMPCO was selling the socket for about $30, I think the price is now, $18. Each pipe has a locking ring which has to be removed before retorquing.

The retorquing is easy to do but if you do not do it right, you may damage the fuel injection pump. I do not have the instructions with me.


David

[This message has been edited by be459 (edited 11-03-2000).]
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  #10  
Old 11-03-2000, 07:13 AM
CJ CJ is offline
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Thanks for the update. I am looking at my car and a picture of the repair manual. What I see on top of the pump are 5 big pipes (big in comparison to the fuel piping that runs out of these pipes on it's way to the injector) with grooves in them. I assume that these are the pipes are the ones that require a special tool to to retorque. When retorqing is it required that you disassemble it and put in a new washer, since the old washer may have been flattened already or may I just retorque them?
I do appreciate everyones help here. What really amazes me is that not one dealer in the Baltimore area could figure this out, but when I have explained to them the theory, everyone seems to aggree that it would work.
Keep up the great work!!!!!
In the mean time, I am going to call the Bosch service center in Baltimore and see if they have any instructions from Bosch on this.
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  #11  
Old 11-03-2000, 08:38 AM
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Yes, a picture would really be handy here. David's explanation pretty much covers it but let me add MB's parts descriptions to the order.

First you remove the injection lines. They were screwed to the "pressure valve holder". This is what needs to be retorqued and yes, the reason is that the leaks may be solved with just a retorque. There are two types of leaks here. One is external (makes a mess) and one is internal (causes rough running and possibly the noises we are discussing). The external leak is from the rubber o-ring and it seals the "pressure valve holder" to the pump body. The second type of leak is leaking the pressurized fuel from the line back into the pump cavity. The parts blow up shows these parts in this linear order: 1 - pressure valve holder, 2 - seal ring 017 997 41 48 (rubber o-ring), 3 - spring, 4- seal ring 004 997 45 40 (brass ring), 5 - "pressure valve", 6 - pump element.

The leak, that matters here, is above the valve and inside the pump body, below the pressure valve holder.

Sure could use a picture.
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  #12  
Old 11-03-2000, 08:11 PM
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Upon closer examination of the pump on my car, it appears that there are little yabs that lock down the valves to the pump in addition to being screwed in. Does anyone have a proper way to replace these seals and/or torque them down.
The loacl Bosch shop needs to see the pump in person to look at the metal ID tage, that is riveted on the side. He cautioned me not to touch this unless I knew what I was doing. He stated it is easier to break it than to fix it.
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  #13  
Old 11-04-2000, 10:02 AM
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Performing a retorque on the delivery valve holders is easy for a Bosch pump man. I would recommend that you have a Bosch service mechanic do the job on-engine. They have the serrated socket, the copper washers and o-rings if needed, the torque specs, and last but not least, the experience.

Also, ask the Boschman to try loosening one high pressure line at a time in order to isolate the nailing cylinder. Have him do this prior to the re-torque.

------------------
Jake
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  #14  
Old 11-04-2000, 09:31 PM
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Guys, this is an interesting thread and I have followed it all the way through. Now I find that I simply must expose my ignorance. I seem to be the only person who does not understand what "nailing" is.

My car is noisy and it may be "nailing", but if it is, I wouldn't know it.

Would it be possible for someone to expand somewhat on how to recognize this problem when it occurs?

Thanks in advance for your response.

------------------
Ted
1979 240D
160,000 miles
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  #15  
Old 11-07-2000, 01:06 AM
CJ CJ is offline
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Ted,
Nailing is when your diesel is making a louder than normal tapping sound, during the combustion cycle of the engine. If your car is making this loud tapping, I would suggest checking your valves to make sure that they are properly adjusted. Cars with solid lifter should have the valves checked/adjusted every 15K miles.
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