E320S4 Engine/Pulley Chatter
 

I got home tonight to the wife saying, "I want you to listen to my car." Great!!

There is a chatter that appears to be coming from one of the pullies on the serpentine belt. It only chatters at low engine speed. Off and on with car idling in park or neutral. More prevalent with the car in gear, stopped, idling.

It seems to be coming from a what appears to be an idler pulley above and to the right of the crank pulley as I'm looking at the engine from the front. It is just below and to the left of the oil filter. The back (flat) side of the serpentine belt runs across this one.

Is this in fact an idler? Why would it be chattering? A tool handle on the torx type bolt sticking out of the middle of this pulley reveals a pretty good vibration in it too while chattering. Do we need to park it?

I would take your car in right away to get this looked on. This sounds like the problem with the rubber ring failing around the crankshaft pulley.

I would recommend everyone what has an M112 & M113 engine to get the rubber damper replaced with the modified version. List price is only $70. & with correct tools the job can be done in under 3 hrs on any of the affected engines. Modified part number on the damper is 112-035-09-00 OR 112-035-08-00.

The rubber ring around the crankshaft pulley will show wear/cracks and Will Come LOOSE as the CRANK PULLEY is a Two Piece Pulley!! And When It Does WATCH OUT! The Pulley Will TAKE OUT the Front cover/water pump oil pan and anything else in its way out!

A co-worker of mine had this failure in her '98 E320, and started with a thump thump noise. The noise was the drive belt being shreaded due to the balancer loosing the rubber ring causing the balancer shifting toward the engine block creating the drive belt to shread the inter two ribs.

From my experience on reading posts on this website and talking to my mechanic, there is not always an early warning. The noise you're hearing just might be your "early warning".

Hear are the results of a search under "harmonic balancer":

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=377362&sortby=lastpost&sortorder=descending

Here are the results of a search under "crank pulley":

http://www.peachparts.com/shopforum/search.php?action=showresults&searchid=377364&sortby=lastpost&sortorder=descending

As we are 50 miles down a mountain to the nearest MB Dealer (Winston-Salem), I'm thinking "Roll Back".

Well, the pulley is not that hard to inspect. (sounds more like the tensioner went south to me). Just look at the rubber between the outer ring and center section of the pulley, if it protrudes, its bad, if the front face of the 3 parts are not aligned straight, its bad however, these are more known to make these interesting scraping sounds rather than a rattle. Look at the tensioner while running and see if its hammering, turn the wheel full lock and load the motor while looking at it, if its bouncing in time with the knock, there you go, bad tensioner. The down side to the balancer is the fact it tends to walk rearward and eat the oil pan. The adds up to big bucks especially if it makes contact with the timing cover.




Joe

I wonder if Sparta is not too far from Raleigh....

Joe has helped a lot of people on this site and has had many members take their cars to his shop.

Always like to see people "support the team"...;)

Thanks for the help guys. I think I have it in order for the moment. Car is covered under trhe Starmark through October. MB - Winston Salem just told me to call their contracted towing service and have it picked up from our house. I will be interested in the failure mode though. I'll report back when I know more. Thanks again!

-Scott

Diagnosis
 

Mechanical failure - Tensioner pulley.

Towed in (roll-back) to MB dealer as a precaution due to crank pulley history as pointed out by Len Sokoloff and others. Repaired, back home safe and sound, compliments of Mr. StarMark.
:-)