New noise, might be bad

[Oldwolf]

1993 W124 300D, OM602.962, 170,000 miles

Lately I’ve been hearing an occasional sound at about 1500-1800 RPM, mostly while turning corners, but sometimes when accelerating in a straight line, a “clack-clack-clack” sound. Mostly it clacks once or twice, sometimes three times, and not very often. Idle is fine, highway operation is fine.

What I have eliminated so far and with the serpentine belt off:
Belt tensioner pulley – spins freely with no bearing looseness.
Water pump bearing – has no apparent play.
Alternator – spins freely.
Fan clutch – 25K miles on it and uggh, has bearing play, but not source of noise I think.
A/C Compressor – The sound happens with the A/C off, but the compressor pulley spins freely.
Engine mounts – bolts are tight.

Yesterday I found that I could just barely get it to clack when I manually adjusted the throttle using the linkage.

Am I missing any other possible source?

My focus is now to determine if it could be cam chain noise. When I bought the car a mechanic told me that the head and tensioner plunger looked new. Mileage on both is unknown but I have put 35k on the car in the last two years since I bought it. No idea if the chain is new.

What should be my next step?

I am guessing:
Check for chain stretch – I’ve read the threads on this.
Check the tensioner plunger - Not sure how to do this. The FSM says the plunger should be charged with oil though. How do I check this and the overall operation of the plunger?
Check the chain guides. Not sure how to do this but the FSM does give some pointers.

What do you guys recommend?

I really hope it is not chain related.

I am apprehensively waiting for your comments.

[compress ignite]

B. The Hydraulic Tensioner Should be VERY Stiff to operate by Hand.
[When removed]Otherwise it's in need of replacement.
[A New(Or DRY) Tensioner Should be Immersed in Clean container of FRESH
Motor Oil and whilst immersed "Operated" to fill it with oil.]

If you can get Whatever "IT" is to CLACK whilst stationary:
1.Motor or Transmission mounts(Specific Height Tests for the Motor Mounts)
[Tight Bolts, Means Bupkis]
2.Timing Chain Apparatus
3.The aforementioned (And Accursed) Serpentine Belt Tension-ing System.

Do Not Discount the Injectors!

Harbor Freight:Inexpensive Mechanic's Stethoscope...Invaluable!

"Fan clutch – 25K miles on it and uggh, has bearing play, but not source of noise I think."
(Suspicious!)

[RAYMOND485]

1984 300D TURBO 157K
CHECK YOUR FRONT WHEEL BEARING, I HAD SAME NOISE WHEN BRAKING RIGHT OR LEFT, REPLACED WHEEL BEARING

[Oldwolf]

Originally Posted by RAYMOND485

1984 300D TURBO 157K
CHECK YOUR FRONT WHEEL BEARING, I HAD SAME NOISE WHEN BRAKING RIGHT OR LEFT, REPLACED WHEEL BEARING

I forgot to mention that I have verified tightness of front wheel bearings although the "clack" on some turns does sound suspicious.

Also, I did get it to clack slightly when engine on and parked in my garage.

Thanks for the tips.

[Oldwolf]

Originally Posted by compress ignite

B. The Hydraulic Tensioner Should be VERY Stiff to operate by Hand.
[When removed]Otherwise it's in need of replacement.
[A New(Or DRY) Tensioner Should be Immersed in Clean container of FRESH
Motor Oil and whilst immersed "Operated" to fill it with oil.]

If you can get Whatever "IT" is to CLACK whilst stationary:
1.Motor or Transmission mounts(Specific Height Tests for the Motor Mounts)
[Tight Bolts, Means Bupkis]
2.Timing Chain Apparatus
3.The aforementioned (And Accursed) Serpentine Belt Tension-ing System.

Do Not Discount the Injectors!

Harbor Freight:Inexpensive Mechanic's Stethoscope...Invaluable!

"Fan clutch – 25K miles on it and uggh, has bearing play, but not source of noise I think."
(Suspicious!)

I was not aware that an injector could cause this kind of noise. Sounds like a metal rap-rap.

I still have my old fan clutch, I could reinstall that to see if the noise goes away.

Can I remove the tensioner w/o any problems occurring to the guides?

But first, I want to eliminate the cam chain as the problem. What is the best procedure to do this? OR- maybe the tensioner should be checked first?

Does cam chain noise occur only at a narrow RPM band like I am hearing?

I need to find the test heights for the motor/transmission mounts.

Thanks.