300 "ping" problem solved

I had an earlier post about my 1993 300E2.8 with a "ping" at idle when the a/c compressor was on. The ping sounded very much like ignition knock but was only there with the a/c at idle. The post was:

300E Pinging with A/C on

I finally found the source of the problem. It was a defective damper or shock absorber on the belt tensioner. After replacement of the shock absorber, everything is quiet again. It is still amazing to me how much it sounded like ignition knock but I was almost certain it was not from the beginning because it was never present when you would expect ignition knock.

Just an additional note: As I understand it, on the 300 engines up until some time in the 1993 or 1994 time frame, the shock absorber is separate from the tensioner; on later models, it is one piece unit.

Brother of The Benz,pfphipps
It's amazing how many DIYers, and even a pro has been lead down the pathe of mis diagnosis by that little rascal.
We have as you, thought of PING, lifters, timing chain or even the loose nut behind the wheel.
When all along it was a shock absorber in minature size.
So happy you've solved your problem.
Happy Trails Beep Beep from The Spiderman in Houston!!!

[alan911]

I've got the same problem on my 300SDL. Did you change the damper yourself or have someone do it ? How much of a PITA is it to DIY it ?? What has to come off or apart ?? The rattle at idle is driving me nuts

thanx

[renok7]

Alan911,

You can solve your problem for a quarter. Get yourself an O ring and insert it between the top bushing and the washer at the top of the damper. Over time the bushing gets sloppy and vibrates. The O ring picks up the slacks and stops the vibration. I did it over a year ago and it is still fine.

Reno

[alan911]

If this works, you da man ! I'll give it a shot in the A.M.

My Mech. said it's pretty common for this thing to cause the noise. He held his hand over the top of it and the noise stopped. He wants $150 for parts and labor. Says its a major pain in the A$$ to replace it. He's probably right.

You can imagine how I felt to know it was just the damper. I had other hellish visions of timing chain, Rails, etc. going out.

Judging from earlier posts, it leads to a lot of mis-diag. of problems.

Thanks again.

[alan911]

O-kay... Looked at the Damper again this am. The bushing at the top of the damper is o.k.

However, the bushing at the bottom of the damper seems to be the culprit and is slopping around and not tight as I can slide it back and forth on the bolt...

Now.....what to do next. What has to come off to take the damper out and replace it ??? Damn !!

[renok7]

Did you try the O ring trick on the top bushing?

If you haven't you should do so before doing anything else. Didn't you say the rattle stopped when your mechanic put his hand on the top bushing? The O ring will do the same thing. Trust me

[alan911]

OK will give it a try. Do I take the top bolt out and just slip one (1) O ring next to the bolt head ?

[alan911]

Woops ---just re-read you post. Next to the washer and the bushing.........got it.

[renok7]

The O ring should be just large enough to fit over the bolt shank and fairly thick (1/16" or so).

Good luck.

Reno