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Metallic sound from 6.9 engine front end?

Started by Jan S, 09 May 2022, 10:22 AM

Jan S

Engine is a 1977 US 6.9

I know this is a difficult one ... a verbal description of a sound. I'm giving it a try to see if this is a familiar sound to some of you.

-- The metallic sound comes from the front end of the engine
-- Only when engine is cold
-- It seems as if the sound goes through four cycles per second at 1000 rpm
-- It seems to be a combination of a scratching and rattling sound

Could it be the water pump? Since the noise disappears when warm ...?

Probably not the chain guides/tensioners?

Doesn't seem to be the alternator.

Any views/assessments is highly appreciated. A metallic sound from the engine is no good for my sleep  :'(
1975-mod W116 450 SE with 6.9 engine


As a very general guideline noises at engine speed are from the bottom end and at half engine speed from top end.
So approx 10 taps per second @ 600 rpm would be bottom end noise and 5 taps would be top end.
Would be best to try and link a clip.  Indeed noises can be a pain to pinpoint.
Try and get a mechanical stethoscope. They are pretty cheap and can help you localize the noise.
1977 450 SEL 6.9 - Astralsilber

Jan S


I follow your logic regarding bottom end and top end. In my case it should be closer to 16 and 8 taps per second (1000 rpm).

My sound is somehow continuous, with variations like a sinus curve, approx. four cycles per second. My subjective assessment.

I will try to record it tomorrow, to see if the noise can be separated from the general engine sound.

The suspect I have in mind is the water pump. Has anyone experienced that sound? Does it vary with operating temperature?

I will read me up on the use of a stethoscope. Thanks for the tip.
1975-mod W116 450 SE with 6.9 engine

Jan S

Bought this stethoscope today.

The patient was in a good mood today, i.e. the noise could be heard in part as sharp ticks, but not as distinct as normally. And only for a short period.

After a few minutes the noise disappeared. I were able to check the alternator, water pump, power steering pump, exhaust valve area on both sides, front end in general e.g. where the chain and guides sits, top of valve cover.

All seems to be fine, for an untrained ear.

But I need to remeasure later when the noise is heard clearly.
1975-mod W116 450 SE with 6.9 engine


Also listen to the SLS pump, might be coming from here.  Unless you don't have it as I think you don't have hydro suspension?
1977 450 SEL 6.9 - Astralsilber

Jan S

Right, I don't have hydro suspension - it's a 450 SE but with 6.9 (a previous owner replaced the original 4.5 liter. And removed the AC and washer tank, among other things  >:(  ).

I checked again today. No noise, engine runs beautifully.

I have to wait until the noise is back. Annoying.

In the meantime ...

-- Could it be the fan clutch?
-- Could it be the crankshaft pulley?

At some point I might have to remove all the belts and let the engine run for a minute, to see if the noise disappears. Should be fine for the engine, I guess?
1975-mod W116 450 SE with 6.9 engine