Mysterious engine noises

[ja17]

Hello group,
List all your mysterious engine noises here with fixes!

Here I one I mentioned in a past posting:

If the valve cover hold down bolts are overtightened, the brackets will distort inward causing them to rub against the camshaft. The noise may sound like a loose valve adjustment.

Here is a picture of a customer's who lived with the noise for years. The more he adjusted the valves the louder it got!



Download Attachment: valve cover holder rubbing camshaft.JPG
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Download Attachment: vc braket wear.JPG
33.64 KB


Joe Alexander
Blacklick, Ohio

[Ben]

Mmmmm good idea for a thread Joe !

I had an odd tapping sould which turned out to be the air tube from the slide valve to the CSV banging against the rear of the block or the inlet manifold. I had missed a bracket on reassembley and its orientation was slightly wrong causing it to rub !

Took me a while to find that !

Also had a terrible noise from the distributor when I recieved an incorrect but ALMOST identical rotor arm that was contacting the cap. I had fitted it and drove off witht the radio blaring, as usual, and didn't notice it for a few days. When I heard it I didn't immediately relate it to the recent rotor arm replacement !

Maybe we should start a thread on suspension noises.....I have plenty !!  :evil:

Regards,
Ben in Ireland.
'64 230SL 4sp.

[Douglas]

Joe, how much damage did this do to the camshaft?

Douglas Kim
New York, NY
280 SL #016220

[113gray]

I just went to loosen my valve cover bolts after reading Joe's post! I have not been able to find a correct torque for these, even in the TDM. I noted my valve cover brackets were distorted in a spiral configuration (top twisted clockwise) when I had the cover off a similar engine recently, no doubt from years of overtightening. No contact with anything however.  
My engine noise is a soft thunk-thunk @ idle that disappears on warm-up & on engaging (depressing) the clutch. No other symptoms, but my engine has 230,000 km (150K mi.). We discussed this at a Tom Sargeant "gathering" in '03 & the consensus was worn bearings allowing the crankshaft to move forward a few thousands of an inch on engaging the clutch, quieting the noise.  Fix: Ignore. (Until my engine needs a rebuild for more pressing reasons.)    -JP-

[Cees Klumper]

Speaking about noises ... engine noise in my car was dramatically reduced when I found and plugged some holes in the firewall. Holes and even small cracks can let through a LOT of noise. I also closed the gaps right above the windows where the soft-top frame meets the canvas, with black foam strip. Just today I was considering fabricating out of foam two sections that will fill the only gaps remaining open to the road with the soft-top closed. The ones directly behind your + your passenger's shoulder, so just aft of the side windows. When you look through, you can see the road. I imagine with these gaps closed, the road noise with the soft top up will be dramatically reduced.

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[ja17]

Hello

Doug, the condition caused not damage to the camshaft. It rubs on an area between the cam lobes.

Jim, I agree with the diagnosis on the crankshaft moving fore and aft a bit. Early engines had "thrust bearings" attached to the #3 main bearing caps which limited fore and aft movements. The factory specs are .004" clearance. If you force the crankshaft in or out at the vibration dampner you may be able to see quite a bit more movement.

Later engines had the thrust surface doubled and built into the #3 main bearing. I agree that it is not serious enough for a tear down at this point.

Joe Alexander
Blacklick, Ohio

[ja17]

Mystery noise #2,
Did you ever have a cricket kind of chirp noise in time with your engine revolution? It can be slight but noticable to a good ear.

If the cam on the distributor is not lubed the points run dry causing a "cricket chirp" noise every time the rubbing block on the ignition points runs over a dry lobe on the distributor shaft!

Joe Alexander
Blacklick, Ohio