1991 350SDL. Original owner, 149K miles. Has been a wonderful car.

At idle there is a moderate/loud hammering noise in/on the front of the motor that goes away after a high speed run but returns hours later after running around town. It is not valve lifters, it's a heavier sound. The noise has been around a good while, it's not getting worse.

Is there anything with the timing chain that relates to these symptoms? If it was the sepentine belt shock wouldn't the noise be there all the time at idle?

Thanks for any ideas.

ez,

It could very possibly be the belt tensioner assembly. The noise varies depending which part is failing.

There is also the lesser possibility that the engine, known for its tendency to bend rods, is doing serious damage to its cylinders. Has oil consumption increased?

ewstan

My engine with 2 bent rods was actually quietet than the new longblock they installed

I would look at engine shock and valves...maybe try some fuel treatment?

If you are the orginal owner and you have made it to 149K you probably have no worries
I think the majority that are going to blow go before or right around 100K



Warren
1992 300SD 162K
Columbus Ohio

This is turning into quite a 603.97X engine forum!

My 1991 350 SDL has been through a tensioner "damper" (shock) every 18 months or so since new ... I recently bought the tensioner device that holds it on and will replace both the damper and the tensioner to see if it will last longer ...

Failure indications are usually aural and can run from a light ticking to a chain ticking sound all the way up to very, very loud hammering noise ... varies depending on rapidity of failure and I guess other stuff. They immediately go away when the damper (shock) is replaced ...

Have ordered the parts from Fastlane ... best prices.

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

Thanks for the info George.

Would you be kind enough to describe the procedure for replacing the shock? Do you have to remove the radiator and fan hub? Is it hard to get the tension on/off the serpentine belt?

Thank you.

The wheel lug tool fits in a hole near the top spring perch to release tension. Seems like something MB learned from Chevy.

Sixto
91 300SE
87 300SDL
83 300SD