Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 05-11-2009, 10:04 PM
Registered User
 
Join Date: Jul 2008
Posts: 117
Tracing Down Knocking Sound

Hello,

So I am now in possession of a W123 parts car which has a knocking sound in the engine. I do nto have much experience with knocking, so I'm looking for some advice on tracking it down and seeing how I can possibly quiet it down. My objective is probably not to save the engine, but just be able to move it around for parking reasons in my street or driveway.

I have heard talk that sometime knock can be do to an injector, a spun bearing, or a "rod".... I'm wondering where I can efficiently start to narrow it down. If it's any of these, would finding the associated cylinder and loosening up the injector quiet down the racket, or reduce further damange rate to the engine when run like this?

Any tips or tutorials on the ways of knocking sounds would be much appreciated. I'm afraid to say that I don't even know what a "rod" is...

Thanks.
Reply With Quote
  #2  
Old 05-11-2009, 10:25 PM
Diesel911's Avatar
Registered User
 
Join Date: Sep 2007
Location: Long Beach,CA
Posts: 26,474
How about somemore info. Is it a dull rythmeic sound or a higher pitch sharper sound?
How much is your Oil pressure when the Engine is hot and it is ideling?

To narrow down which cylinder it might be hopefully it knocks at idle- Loosen 1 of the Injector Hard/Fuel Injection Lines/Tubings up at the Injector at a time on each Cylinder. This will cut off the Fuel to that particular Cylinder.

If that knocking dissapears or the sound of the knock lessens that is the problem Cylinder.

After that to find out if it is the Injector or not switch the one from the suspected bad cylinder for another Injector (the one furtherest away). If the Knocking Sound Follows the Injector from the suspected Cylinder it is the Injector that is haveing a problem.

If the knocking sound stays in the same Cylinder after switching Injectors there is a good chance that you have a Bearing gone bad or some other problem in that cylinder.

If you model has a little steel Oil Pan you can drain the Oil and remove the pan and look and see if pieces of bearings are in the pan. The Oil Filter could also be pulled and inspected for bearing fragments.

Sometimes when a bearing is going bad the Oil Pressure Gauge pointer will fluctuate up and down.

Also be sure that the Knocking sound is not coming from something loose like a loose Air Filter housing beating itself on something.
__________________
84 300D, 82 Volvo 244Gl Diesel

Last edited by Diesel911; 05-11-2009 at 10:32 PM.
Reply With Quote
  #3  
Old 05-11-2009, 10:35 PM
Diesel911's Avatar
Registered User
 
Join Date: Sep 2007
Location: Long Beach,CA
Posts: 26,474
Please put your year and model in you signature so it will appear evertime you post.
This is a Russian Parts site but most of it is in English. You can use it to learn the name of the parts and where they go.

http://www.detali.ru/cat/oem_mb0.asp?TP=1
__________________
84 300D, 82 Volvo 244Gl Diesel
Reply With Quote
  #4  
Old 05-12-2009, 09:52 PM
Registered User
 
Join Date: Jul 2008
Posts: 117
1977 300D/ W123

The car is a 1977 300D/ W123.

The knock is not high pitched really, but kind of a clank-clank. It sure doesn't seem like a hose or belt slap sound, but I guess I could check.

I'll also try pulling the injectors or tubing to each cyclinder and seeing if I can narrow it down or eliminate the sound at idle at all... The guy I bought it from said he thought it was the number two cyclinder, so the cylinders are counted from facing the fan/radiator and back towards the firewall, right?

Thanks again all.
Reply With Quote
  #5  
Old 05-12-2009, 10:38 PM
oldsinner111's Avatar
love all animals
 
Join Date: Nov 2008
Location: bristol,tn
Posts: 5,272
Try tightening crank pulley bolt,oil filter,intake,exhaust,turbo and check air filter mounts.Then look,one thing that can fool the best,flex plate behind flywheel.
__________________
let not forget the flower power,hippy and veteran

Last edited by oldsinner111; 05-13-2009 at 07:11 AM.
Reply With Quote
  #6  
Old 05-13-2009, 12:17 AM
Registered User
 
Join Date: Jul 2008
Posts: 117
Flexplate

So checking the flexplate would involve dropping the tranny or pulling the engine would it not?

What is the common failure with this component? Would I be able to do the old garden-hose stethescope trick and localize or pinpoint the sound down in the region of the tranny?

Would it go away if I put the car in Neutral?

Thanks again.
Reply With Quote
  #7  
Old 05-13-2009, 07:11 AM
oldsinner111's Avatar
love all animals
 
Join Date: Nov 2008
Location: bristol,tn
Posts: 5,272
No you can see plate thru inspection cover.I do not now how to replace,wrong not oil pump,but filter housing..
__________________
let not forget the flower power,hippy and veteran
Reply With Quote
  #8  
Old 05-13-2009, 11:55 PM
Registered User
 
Join Date: Jul 2008
Posts: 117
"injectoring nailing" and "cracking each line"?

I've been reading up on possible knocking sound causes in other posts and have run across reference to "injector nailing". Can someone explain what happens to cause this and what it is?

Also, related to this, how do I "crack the hard lines" to each injector (one by one) to narrow down which injector might be nailing?

I'm still hoping for an explanation of flex-plate failure which one might miss-diagnose for rod-knocking...

Thanks.
Reply With Quote
  #9  
Old 05-14-2009, 12:30 AM
FLYWULF's Avatar
Registered User
 
Join Date: Jun 2007
Location: Third rock, left coast
Posts: 102
cracking and nailing

Hello, cracking a line is simply loosening the nut that clamps the line to the top of the injector. Don't take it all the way off, just loosen it enough to release the fuel pressure. small amount of fuel will bubble out of the top and bottom of the nut each time the pump delivers to that injector.

Nailing.....I have heard of it as well but I am not sure what it is.

Cheers,

EddieE
87 300SDL 325K
Reply With Quote
  #10  
Old 05-14-2009, 01:21 AM
Registered User
 
Join Date: May 2007
Location: Out in the Boonies of Hot, Dry, Dusty, Windy Nevada
Posts: 9,585
Here are some good pictures of a cracked flex plate

www.peachparts.com/shopforum/showthread.php?t=237244

Charlie
__________________
there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
Reply With Quote
  #11  
Old 05-15-2009, 08:09 PM
Registered User
 
Join Date: Jul 2008
Posts: 117
Rods?

So are "rods" the piston arm which connect the piston head to the main crankshaft/propeller-shaft, or are these push-rods which control the up and down movement of all the piston-cylinder valves via a rocker-arm system?

I'm just starting to learn about the venerable five-cylinder mercedes diesels...
Reply With Quote
  #12  
Old 05-16-2009, 09:47 AM
toomany MBZ's Avatar
Registered User
 
Join Date: Nov 2006
Location: central Va
Posts: 7,820
^^These are overhead cam engines. Open the oil cap, you're looking at the cam. So a "rod" is the piston arm, (connecting rods) but the weakest point is the wrist pin. IF that's the case, and make sure, sounds like a trashed engine.
__________________
83 SD

84 CD
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 12:09 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page