Bucket O' Nails Sound from exhaust

Over time my 80 911SC has gotten noisier and noisier. It sounds a though there is a bucket of nails bouncing around inside the exhaust. Is this a sign of a car in need of a top end rebuld? (BTW, the exhaust is a new SSI/Muffler combo - the louder exhaust has magnified the previously existing sounds)

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Eric Purdy - 1980
911SC

I had the same problem on an older 2.4 What happened was one of the cam tower/head bolts backed off and created a leak between the jug and head. Sound like a machine gun going off and followed the engine RPM's. Had to take a valve cover off to find it.

Rsnake, did your engine leak oil from between the cam tower and cylinder when that happened?

Could it be tensioners? Most people describe that sound as dragging a chain out of a bucket. Could the sound be coming from the cam housings?
Bobby

[This message has been edited by Bobboloo (edited 04-04-2001).]

Eric,

I suggest a compression check on a cold engine, ASAP, to see if any cylinders/heads are loose.

If that is inconclusive, then start it up and be prepared to immediately probe the cam chain covers/cam box area with either screwdriver/wooden dowel to the ear, or mechanic's stethoscope to see if a tensioner has failed! Subjective descriptions of noises don't always jive with how individuals perceive the sound. Loose cylinders have always seemed like a spitting exhaust leak to me ... at idle, on a cold engine. Tensioner failure always sounds like a chain being dragged out of a trash can to me! But, others describe the same problems differently.

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Warren Hall
1973 911S Targa

Thanks for all the replies. Let me add a little more info:

1) New Carrera style tensioners 2 years ago - The sounds are not coming from the chain housings.

2) Compression on all 6 cylinders is 160-175. (Is this too high for an engine with 9.3:1 compression? - i.e. lots of carbon)


3) Head studs are all solid and torqued properly.

4) Valve lash has been adjusted on 3 occasions in the last 5K and required little or no tweaking by me to meet spec.

5) The sounds are not of the popping type caused by broken head studs under acceleration.

As you can guess, I'm at my witt's end with these sounds. I was hoping it was an exhaust leak but when I put the SSI's and muffler on, I ruled that out. It's a shame because the exhaust sounds great now - what you can hear of it over the nasty sounds. Perhaps I'll try to digitize a clip and let everyone hear it.
Thanks Again.

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Eric Purdy - 1980
911SC

Eric,

If your engine is in good shape in all of the above areas, then I suspect loose/broken baffles within your muffler.

Do you still have your OEM SC muffler? If so, why don't you try adapting it to the SSI outlets, then mount it and test to see if the loose nail symphony is gone?

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Warren Hall
1973 911S Targa

Thanks. One more piece of info I forgot. The muffler is new as well. The beautiful new exhaust just amplifies the previously heard sound. While I had the exhaust off I looked up at all the exhaust valves and they appeared to be in good health visually. There was a uniform whitish coating in the exhaust port area of all six valves and a slight dark area right at the end of each valve guide. This really has me baffled since the engine is in otherwise great shape. My next step is to redo the top end or perhaps the whole shebang but I was hoping to push the motor beyond its current 104,000 miles.

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Eric Purdy - 1980
911SC

Well...I made a recording if anyone wants to take a stab at ID'ing the sound drop me an email.

Better yet! I've posted the files on a free website provided by Apple.

http://homepage.mac.com/ewpurdy/FileSharing.html

Gotta love technology. Let me know what you all think.

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Eric Purdy - 1980
911SC

My guess is your catalitic converter, on my 83SC I had a simmilar noise and it turned out to be my cat pipe, which I got rid of!

No CAT. Just SSI's and a stainless muffler.

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Eric Purdy - 1980
911SC

I hear my (engineer) father's voice: "Isolate, Identify, Eliminate."

Take the muffler off. See if it makes the noise. Get a long screwdriver, and use it like a stethoscope (pressed to your ear) while the engine is running. Get methodical. Find the source.

No chance that your "new" stuff is faulty? Every now and then we can get stuck with a busted part from new. Listening to your wave file, it does sound exhaust related...then again my wife reckons I'm deaf;-)

I think Jack has the right idea, methodically go through everything! Good luck

If the sound had not been there before I put the new exhaust on, I would suspect it as well. This was one of the reasons why I replaced the old rusted exhaust.

I sat and listened to the exhaust yesterday and I noticed the sounds are worst when the engine is cold. As it warms up, the sounds get fainter but are still perceptable. If the heat exchangers are leaking at the flanges, could the exhaust leak make this sound?

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Eric Purdy - 1980
911SC

At 104k miles, I like to think your engine is just broken in. Be sure to exhaust (pun intended) all other possibilities before you start taking the engine apart. It simply does not sound like a piston, cylinder or head problem. It does sound like the guts of an exhaust component are rattling inside their little metal box.

You should be able to isolate this sound. I use a dowel since I do not have a fancy stethoscope. Put one end of the dowel against your head, over your ear, and the other end on the thing you want to listen to (muffler for example). Be sure your end is tight against one of your head bones, near your ear, like you cheek bone, or stick the dowel right on the center of your ear. This method works surprisingly well.

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'83 SC