C220 CDI - Engine Knock

[gdwd76]

Hi Guys i'm new to this forum and to Mercedes ownership but having purchased my CDI over a couple of months ago I'm pulling my hair out trying to identify the problem...hope you can help...

Symtoms..
Metalic knock in time with the camshaft and increases in speed with rpm, from doctors stethoscope it appears to be back right (cyl 4)...

Things that have been done....
Visited Merc, they said sticky lifter so changed all 16 ...
Whilst rocker and cams out checked chain and oil delivery...............
Have changed injectors and checked via star status of all and all are performing as they should.
Have completed comp test and all four cyclinders reading 25bar...
Have replaced fuel pump (high pressure on front of engine)...................

engine noise still present and now running out of ideas..........................it does not affect the performance nor does it through any codes or smoke of any kind out the pipe in fact the car peforms as it should..............

Any help would be greatly appreciated, as like i said with no obvious faults i'm coming to the end of my patience and also wallet!!!.....

Help .............Help

 

[Xtractorfan]

Broken valve spring..also possible injector knock, try loosening no4 pipe to injector when engine running and check if noise stops.. also have you tried flushing oil just incase one of the lifters isnt getting fully oiled..

 

[gdwd76]

Would the compression test not have identified the broken valve / stem?, when the lifters were re-fitted they were oiled up and the engine cranked on battery ensuring visual confirmation that all were being oiled and oil passing to the cam.

In further attempts to resolve this I have had the injectors tested in a rig and all have proven to be within tolerance!, i refitted them with new stretch bolts and copper washers and no leaks from the top but yet the noise is still present.

When I had the car on the stands today I decided to use the scope to check for noise underneath and from the sump above the steering rack it was obvious the noise was loudest here although could have also just been me wishing to locate the noise...anyway when i moved the scope across the pan from drivers side to passenger the noise decreased considerably.............

This is now making me think I will probably remove the cover and have a look, as i understand it the bearing caps if showing signs of wear can be replaced without head removal, is this also the case for the conrod as would be good to see if any tolerance in these at the same time..............can anyone confirm if this is the case?????????? can i do this without removing the head and conduct all investigation and if necessary repairs works from sump area?....

I've read a couple of posts on folk suggesting conrod bent etc and some of the threads on here are very informative about their replacement so I'm not daunted too much by attempting this but does anyone think or feel that this could actually be the problem?................and more importantly why would this occur on a vehicle with only 41k on the clock?............the car was involved in a light front end crash but nothing structural............

Any help greatly appreciated as if i replace any further parts I may as well just replace the engine?...............

Thanks guys and look forward to hearing your thoughts ...

Ed

 

[Xtractorfan]

You cant replace or even check a conrod without removing the head and the sump, the piston and conrod have to come out thru the top of the engine...

 

[Guill Roefs]

Hi Ed
I know it is a long time ago, but did You ever find the cause of Your Problem?
I am interrested as I have the same issue 1000Km after a small collision on the front.

Thanks to let me know

Guill

 

[lloydscarrs]

Hi

I have the same issue on my 203.
Did you ever find out what the issue was with yours ?

Thanks

 

[ajlsl600]

Broken valve spring..also possible injector knock, try loosening no4 pipe to injector when engine running and check if noise stops.. also have you tried flushing oil just incase one of the lifters isnt getting fully oiled..

Wud say if valve spring brokr ud be runnin a very noisy triple!!

 

[Botus]

broken pistons is common

 

[ajlsl600]

Pt of skirt. Maybe. I guess these are not 2 pt pistons? Back off fuel pipe 1 by 1 see if noise changes.or run a diagnostic cyl cut out test.