pcy

Guys,

I am hoping you guys can help me decipher the knock knock sound on my '04 C320 4Matic with 78K miles.

The noise is more of a metallic knock knock and is pronouced while the gear is in drive/reverse and brake is fully on (meaning, car is not in motion). When I shift the gear to Park or Neutral, the noise subsides significantly and reduces to a faint noise. The knocking noise sounds like it is coming from the front of the engine but difficult to be sure.

Idler Pulley is new, Water Pump is new. I checked ALL pulleys and they are all in perfect condition. Belt tensioner is NOT the cause of this noise. Oil has been changed less 500 miles ago with 0W-40 Mobil1.

Any suggestions on how to narrow down the root cause of the noise?

MW_ATL

I doubt this will be your issue, but...

I had a similar noise on mine and it about drove me nuts for a couple of months. We still have no idea what happened, it looked like I had backed into something and the entire exhaust was twisted a bit, so that a pipe near the engine was touching when the car was in gear. We had to put it up on a rack to find it. There was also no "physical" damage, just everything torqued around.

I am *sure* I didn't back into anything and we still have no idea what caused it, but we loosened everything up, tugged a bit and then re-tightened all the bolts and the noise went away. It was very similar to what you are describing. I have chalked it up to road debris on I-285

pcy

MW_ATL, thanks for your feedback. I really wish my car's problem is that simple.

mleskovar

You make it sound like there is no noise when the car is in motion...true? Does it change in frequency or loudness if you change engine speed (stopped or not, obviously you can't rev more than a couple hundred RPM with brakes on)? You need to narrow down the source better...engine or transmission. Get a stethoscope or use a screwdriver/hammer handle to the ear.

pcy

mleskovar, I wasn't clear in my description, sorry.
The noise is there (around 20% of the noise) even when the gear is in park and neutral. When the gear is moved to drive or reverse, the noise gets amplified and the noise frequency (revs per sec) decreases. While I am driving the car, I can't tell if the noise is there or not due to the engine and drivetrain noise.

I tried using a long ratchet extension and I wasn't able to locate the source of the noise. Currently, there is a snow storm in Boston area. So, I will continue this investigation tomorrow.

Glyn M Ruck

Check rear transmission mounting for condition.

Try & find the source of the noise. If it's engine I hope it's minor - I will link you to C320 Make's thread. Sincerely hope it's not the same.

Glyn M Ruck

Here:

https://mbworld.org/forums/c-class-w...nop-noise.html.

We PM'ed backwards & forwards & it was multiple small end bearing failure.

Good luck!

EDIT - this was the final outcome in PM

Hello. The engine is open. Damage to the connecting rod bearings. Each bearing after a little, shiny surface broken. Rod necks are a little scratches, they will be refined machining. Ok cylinder, piston ok

When the engine is open both at the same time we put the new: the crankshaft bearings, oil pump, piston rings, key chains and rails, Is there any other that it is wise to put a new one?

What could have caused rod bearings wear? Too long in the same oil? Oil pump defective?

this is wery expensive, but....

pcy

Thanks Glen for your feedback. I guess it's almost as good as rebuilding the engine. I wonder how long i can drive the car like this... would continuing to drive like this cause further damage?

The noise is loud sometimes and other times, it's not as loud. I can't tell what changes the knocking noise level (except changing the gear from Drive/Reverse to Park or Neutral).

Glyn M Ruck

Try to establish whether this is internal engine noise or something external. Bearing failures on V6 Benz engines are incredibly rare - even at extremely high mileage. e.g. 700,000Km

pcy

Glen, I replaced the trans mount about 2 months ago. I bought the trans mount at MB dealer. So, trans mount is highly unlikely the cause of the noise.

pcy

Here is a video file - car is in Reverse with parking brake ON. When I was recording this yesterday, the noise isn't that prominent, but I will update the video when the noise is a bit louder.

http://www.youtube.com/watch?v=ZegOWTzDN38

pcy

UPDATE: recorded a new file with the belt off (gear is in Drive with the parking brake on).

http://www.youtube.com/watch?v=BvReavqaERY

mleskovar

It sounds like about 2 'hits' per second which is roughly 1/4 of idle which makes it cam train related? Am I guessing correctly here?

Glyn M Ruck

I hear hydraulic lifters & what sounds horribly like a small end bearing or slapping piston skirt.

I hope it's in the top end - PM C320_make & ask him to have a listen.

C320 Make

Hi
Oh no. Sound and this frequency is just the same as I had I am very sure that noise is just same as mine. I remember that very well. it is Sad think. Bad memorys

it sounds just like a rod bearing. Is that your sound come right away as the engine is cold ? Or it comes then when the engine warms up a little ?

pcy

The noise is hardly audible when I start the car. After the car warms up, the noise is audible.

C320 Make

Sometimes the sound is harder and sometimes a little quiet. Circumstance and the oil temperature/pressure. But a flat punch knock 2 per second to the idle
Listen to good rubber tube or a stethoscope with the engine block side, is there Knock Knock sound, it is easy hear, if you are carefully

C320 Make

My car began to knock knock sound when the engine warms up
Cold engine there is no sound because the oil is thick. When the oil is thick sliding bearing is not easy to grasp the neck of the crankshaft. Here is a thick cold oil between

Warm oil is thin and when the bearing sliding surface is broken mid-term is higher, knock knock sound will start when the lubricant is not enough, friction is a major missing padding The oil is too thin then.
If you knock knock sound comes engine block you can do the test if you want. Put an extra thick engine oil in engine and try
If the sound is a little bit quiet now the test is successful

pcy

No performance issue on the engine/car. When I rev, engine performs extremely well... takes off like a rabbit.

I wonder if the problem will get worse if I continue to drive as is...

C320 Make

It does not affect performance
But if the problem is the bearings
Engine complete destruction is assured,
how quickly this will happen. No one can say. If it happens, this is very expensive, or you need new engine. Night's sleep is not worth losing before the thing is for sure. Then when this thing is for sure the matter can be repaired

Bearing noise is "easy" to explore. Believe me. Drive your car crane
and take off the plastic base underneath the engine and tell you friend that he set the gear position of the D and you listening to a stethoscope or a good rubber tube engine block both sides carefully. You can hear the sound if it belong to your block... Or... ask a professional to listen to this

Glyn M Ruck

Hi C320 Make - thank you for helping - sounds like yours - should make the most noise when fully warm & oil thin if it's a bearing. If it was a piston it would tend to quieten as temperature rises & piston expands (slightly). Very little piston expansion on these cars as relates to block. Aluminium piston in Alusil bore.

Glyn M Ruck

pcy - Once clearance in a small end bearing is sufficient to knock it will fail. There will be no impact on performance. You don't want to put a rod through the block or it becomes too expensive to repair. Better off with a used engine. If you catch it now it will be OK. I think better the devil you know & repair the engine.

C320 Make

My pleasure. I am not an expert, but I learn from my car and mb professional mechanic. They tell me something about car engine soul. It was Long lesson, one month Now I am happy

My car connecting rod bearings were just a little damage and sound comes only when engine was warm
But if the bearings are worn out a lot
Much worn often include a knock sound when cold and hot engine
My car connecting rod bearings were just a little damage to the sliding surface. My car was not great damage to the bearings. This was a surprise to me and the mechanic when the engine was open.

pcy

C320 Make, how much did it cost you to repair your engine? What did the repair include?

C320 Make

We changed at the same time crankshaft bearing and all the timing gears and chain, as well new oil pump, piston rings and all the hydraulic valve guides (including all necessary machining) This all is wise when the machine is open

But the only reason was knocking rod bearings
Price the whole thing was about 6000 euros (8142 dollar) Expensive

Conrod bearing replacement is about 3000 euros (4071 dollar)

I just heared my telefon record (Nokia N95) there is my car knocking sound audio sample and it is amazing same like your car noise.. 1/1