S320 CDi engine knocking..
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SLK 230 kompressor
S320 CDi engine knocking..
Just got back after 30 mile drive and the engine is making a definite mechanical knocking noise. Appears to be from the top of the engine but hard to tell. The noise decreases as the engine is revved but is just as noisy when back in idle. I thought the noise would increase when revved if it was a main or small end bearing? But this goes quieter...
Thought (hoped!) it might have been an ancillary, but it sounds top end.
Anyone have any idea where to start to look?
Thought (hoped!) it might have been an ancillary, but it sounds top end.
Anyone have any idea where to start to look?
MBWorld Fanatic!
Joined: Dec 2012
Posts: 2,474
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From: Ball Ground, GA (N of Atlanta)
2003 S500 2007 GL450
Diagnosing noises is difficult while you are listening to them, and much tougher when it is just a description. You did a pretty good description, but the more you can tell us, the more likely you will be to get a helpful answer.
Some things that help with the diagnosis:
Frequency - once per engine revolution, or once every two revolutions (which would be valve noise - excessive clearance, broken spring, etc). A uniform rate, or a double-knock. More at idle, more at higher speeds, same at all.
Quality - With a little experience, you can tell a hard-sounding, sharp metallic noise from a relatively light part, from a softer-sounding, duller noise or a heavier rap from a heavier part. Descriptive terms that help - clink, click, clank, tap, rap, thunk, etc.
Location - top center, top left, top right, bottom, belt area, etc.
Temperature variation - cold engine only, hot only, both, more when cold, more when hot, etc.
First guess from the limited description would be a valve train noise.
Some things that help with the diagnosis:
Frequency - once per engine revolution, or once every two revolutions (which would be valve noise - excessive clearance, broken spring, etc). A uniform rate, or a double-knock. More at idle, more at higher speeds, same at all.
Quality - With a little experience, you can tell a hard-sounding, sharp metallic noise from a relatively light part, from a softer-sounding, duller noise or a heavier rap from a heavier part. Descriptive terms that help - clink, click, clank, tap, rap, thunk, etc.
Location - top center, top left, top right, bottom, belt area, etc.
Temperature variation - cold engine only, hot only, both, more when cold, more when hot, etc.
First guess from the limited description would be a valve train noise.
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SLK 230 kompressor
Thanks wallyp, right here goes!
Uniform rate, approx every second at idle. Sound Diminishes as engine revs increase but return when back to idle. Sounds like middle to front of engine (613.960 diesel). Sound appears to be quite a solid clink or clank but light and not as you would expect of a main bearing, almost as though you feel the sound but can't.
Have only heard it as we got back and then only after getting out of car - S class has great sound proofing!
Does that help, hopefully so as i get manage a head change but wouldn't fancy lifting a 6 cylinder diesel out!
Uniform rate, approx every second at idle. Sound Diminishes as engine revs increase but return when back to idle. Sounds like middle to front of engine (613.960 diesel). Sound appears to be quite a solid clink or clank but light and not as you would expect of a main bearing, almost as though you feel the sound but can't.
Have only heard it as we got back and then only after getting out of car - S class has great sound proofing!
Does that help, hopefully so as i get manage a head change but wouldn't fancy lifting a 6 cylinder diesel out!
MBWorld Fanatic!
Joined: Dec 2012
Posts: 2,474
Likes: 439
From: Ball Ground, GA (N of Atlanta)
2003 S500 2007 GL450
The description should clarify it for someone who is familiar with that engine. Unfortunately, there will be very few people in the USA who are familiar with the Diesel, and I am definitely not one of them.
Not being hampered by facts, I can discuss the issue freely.
No idea what type of valve actuation you have - stuck lifter? Excessive clearance? Broken spring?
Carbon build-up resulting in piston-to-head contact?
Exhaust leak? (It is surprising how mechanical that can sound.)
Once per second would be an idle speed of 60 RPM. If it is a valve problem, occurring every other revolution, that would still be only 120 RPM. At any rate, it sounds slow enough to make me suspect that the noise is coming from the valve gear or exhaust.
Sorry that I can't help more.
Not being hampered by facts, I can discuss the issue freely.
No idea what type of valve actuation you have - stuck lifter? Excessive clearance? Broken spring?
Carbon build-up resulting in piston-to-head contact?
Exhaust leak? (It is surprising how mechanical that can sound.)
Once per second would be an idle speed of 60 RPM. If it is a valve problem, occurring every other revolution, that would still be only 120 RPM. At any rate, it sounds slow enough to make me suspect that the noise is coming from the valve gear or exhaust.
Sorry that I can't help more.
