So what do you think? Noise

[Larry & Norma]

1970 280 SL. When i get up to 60 - 70 mph a loud noise starts from within the engine area. It is perhaps like a dry or bad bearing. It is in time with the engine. If i slow or stop it goes away, making it difficult to find. I think it must be a belt driven unit ie. a) Alternator. b) Water pump. c) Power steering pump. d) Viscous fan. All these appear to be working.
Any ideas as it is driving me mad

[waqas]

If it's any of the belt-driven items, it should be reproducible at the same RPMs coresponding to 60-70 mph. (4000-ish?) Try it for a little bit to see if it shows up, and then use a length of garden hose (or automotive stethoscope) to locate the sound.

If your alternator/water-pump belt is too tight, it can lead to premature bearing failure in either of those components. You can test this by slightly loosening the alternator belt to see if the noise fails to re-appear at speed (don't loosen too much).

I once had a near-death water pump making intermittent aweful sounds from the bearing. The sound would occur at random moments (whilst idling or driving). But I've heard of different failure symptoms in other cars. If yours is the original water pump, you may be able to add bearing lubricant externally (I think) to temporarily eliminate the pump from consideration.

Just some ideas...

[Eminent]

I have the same here for a few weeks now. Some days it is hardly perceptible, the other day it's very good to hear. It looks like the sound is vibrating through the suspension.
Wheelbearings are just changed so i don't think thats the problem.
I know the king-pins are worn. I'm ready to change them, together with the bushings from the upper and lower controlarm and the balljoints.
I'm wondering if it is possible that the noise i hear the play from king-pin is causing to the normal vibrating of the engine at certain revolutions.
Anyhow, i will follow this thread closely.
Gnuface, good luck finding the problem . If you found something, please share it here.
Thanks.
Rini.

[Larry & Norma]

I forgot to mention that i cannot reproduce the noise in the garage i.e. when stationary. This i find a little strange. I am sure it is nothing to do with suspension. I have just removed the fan belt. The alternator bearing seems good. If i wiggle the fan there is a small amount of movement, i am not sure whether it is the viscous coupling or the water pump that has the play. The belt was pretty tight so i may try your suggestion Wagas and run with a looser belt and see if anything changes.

[ja17]

Hello,

How about a little more description on the noise?  Is it a knocking, or a tapping, or a squeeling, or a squeeling, or a  rubbing kind of nioise ?

Be sure to check the viscous coupling on the fan, the water pump, alternator beaings etc. Even a loose fan shroud can get into the fan blade at different rpms.   

[Larry & Norma]

Well Ja17 its a little difficult to describe really. It is definately not knocking, maybe a sort of high speed rattle with a sort of squeal combined which follows engine rpm. I'll have another listen when it stops raining!! Maybe next Thursday!!

[Eminent]

I hope for you. Seen the news and the UK did get plenty of rain last week.
The sound you discribe "sounds" similair to what i hear. I have the idea it comes from the leftside of the engine compartment.
On the road it's good to hear.
If i use the throttle by hand when i'm on the hood it is difficult to hear.
The fan (not the pump) has some axial play.
Will try to eliminate that in a few days.

[Larry & Norma]

Just to update. It finally stopped raining and I got to go for a run today and................ the noise has gone??
Since my last run I have stripped and resprayed the dashboard in the process I dismantled and cleaned the tacho.
Also lubed the tacho cable so I am wondering if that was my noise. Can it really make such a loud noise if dirty?
Sounded really bad. I also slackened the water pump/alternator drive belt a little so maybe.....

[ja17]

Hello,

Yes, I was going to guess on the waterpump.  The noise from the pump will resonate through the fan blades making all kind of noises.  Try squirting some oil into the weep hole of the water pump if the noise comes back.  This will not cure the problem but will confirm the diagnosis if the noise goes away for a while. You can dip a pipe cleaner into some oil and use it to drip oil into the weep hole.