low scratchy noise from engine at idle speed.
 

This is about my E320

I have had this sound since I bought the car and its surely not changed its volume or pitch in the last 18,000 miles of ownership.

I removed the serp belt to test - and the noise was still there, I then used my stethescope to test all parts and the noise is only heard from the front lifting eye of the engine (through which the air pump is mounted)

its a rythmic very low volume scratchy sound like a dry bearing of sorts - The pump is in good shape as it makes its own little machine noise when running and then shuts down.

Im guessing this sound is being magnified by the lifting eye as it is acting like a tuning fork. You can actually hear it if you put your ear near the engine top with the plastic cover removed.

I showed it to a couple of mechanics and one said its a balancer wheel or timing chain problem. The other never heard anything like this.

Assuming M112 engine

Any of this information ring a bell?

M112 engine has a manufacturing defect, or what this is - MBWorld.org Forums

http://www.peachparts.com/shopforum/featured-cars/1582-m112-engine-review.html

Yes I read through those and could not find a resolution. The sound I hear is a perfect rythm of 3 scratch sounds (dry bearing sound) twice every second or so.

Almost sounds like a bad water pump bearing.

The engine otherwise has the typical mercedes sewing machine whine.

I would have to "take it to bits" to find that source of noise.

A friends car is making a similar noise and we think its the water pump. Can you use a long screw driver to touch the water pump on a M112 and put your ear to the end and listen?

I thought the engine had been run with out the belt so the water pump wasn't running

I'm fairly well known for my reading comprehension haha.

Yeah that would rule that out.

I guess we need to ask for video plus sound - paint in the arse when we have to resort to that!

So would it be fair to say 3 scratch sounds twice every second = 6 scratch sounds per second at idle.

Idle of 700 rpm is about 12 cycles per second

So 6 scratch sounds per second suggests camshaft???


How about oil pressure at idle?

Any visible camshaft problems?

Oil spray bars etc etc?

Do a search for "cam sensor magnet" , there might have been an issue with this causing it to rub.

On engines with a timing chain ( like this one ) slightly worn guides / chain can make a scratching noise as the slack side of the chain vibrates.

I think that there was also an issue with the vibration damper ( crank pulley ) coming apart so check for slippage / rubbing.

Can you disonnect the air pump to rule it out?

to answer everyone

the belt was off and I was using a mechanics stethescope touching various assemblies and bolt heads - the noise is loudest at the lifting eye.

I disabled the pump by unplugging it

still the same noise.

The engine counter balancer is placed in the valley of the engine and so are two guide rails for the timing chain pointing towards the heads. Something there is causing this noise to emit and is amplified by the lifting eye (my assumption)

I used chevron delo 5w40 as the first oil in this engine and fleece filter - over time it quietened the overall sound of the engine and became really really dirty. The oil filter previously installed was not pushed all the way on the stalk leaving some area of the central tube uncovered - so technically previous to my oil change the engine was running with no oil filter.

Any bets that would cause rapid chain wear - I think yes, but why has the engine not popped up a timing error?

Me thinks a video is to be made...

You won't have a timing error until the chain jumps or snaps. The motor or ECU doesn't know the chain is slapping the rails.

Zulfigar, even though you unplugged the air pump a dry/worn bearing would still make noise when it was turning due to the belt tension. So the air pump could be the source of the noise. You would need to temporarily install a shorter belt, omitting the air pump, to rule it out as the source of the noise.

The air pump on this engine is not belt driven. Its a full electric item.

I came across this, where he says it was timing chain noise: 1999 Mercedes E320 V6 W210 / M112 Chain Noise - YouTube