I've got a rattle in my engine when I rev it at low rpm that you hear when the engine slows down from the rev. It is on the drivers side and at first I thought it was my power steering pump as the pulley has a tendacy to come loose an wobble but I pulled all belts to assure it wasn't coming from any of the driven accesories. I am leary of detonation as I am running up in the compression range on good pump gas and have previously trashed bearings due to this. I have quieter exhaust then when I last ruined the bottom end so I hear everything that goes on now. It doesn't sound like a diesel rattle and it doesn't really sound like a knock. It isn't consistent for every revolution of the motor so it almost seems like something like metal to metal rattle of a motor mount or something. Anybody got any troubleshooting clues to help me out it would be great. I just hope and pray it isn't something inside the bottom end. It definately doesn't sound like valvetrain.

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71 RS/SS 350
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How loud is the noise and does it change with the temp of the engine? If its louder when cold then I would suspect piston slap, if its when the engine is hot it could be a wrist pin problem as Ive found those tend to make more noise as the engine heats up and oil gets on it making it want to move around more. Sometimes a broken piston skirt can cause wierd noises aswell but thats rare with the better materials used in pistons these days. Your best bet would to be to drop the pan and have a look around since your pretty sure the noise is from the bottomend and take a good hard look at the bottom of the pan too. Almost all bottomend failures show up as metal flakes/particles or big chunks (if the carnage is real baD) in the bottom of the pan.

Check the simple stuff 1st..

Rocker arm/valve adjustment

Exhaust leak from a loose header bolt, or bad gasket.

Get you a pc. of rubber hose (fuel or heater) put one end to your ear and move the other end around diff places on the engine.

When you get to the spot that's rattling you will know it. The hose will make it much louder to your ear.

It's not detonation- that won't happen on over-run, only under load.

Also remember to look for mechanical interference- exhaust hitting something when the motor rocks back and forth, engine brackets, broken engine/tranny mounts, etc.

I agree on looking for outside things. In my opinion, since it's not rpm consistent, then it's not the engine unless there is something under the intake. Some things that sound like underhood rattles can be something under the car. I'd check the motor mount and the exhaust pipe on that side. Those can make noise when letting off the gas.

actually, this sounds like piston rod bearings.

you won't hear them knock until you let off the gas, since as the revs increase the pistons are held tightly in place by pressure. when you let off the pressure (decel) they knock. Still, check the easy stuff first. Can't hurt.

I have the same problem with my 71. The sound is bad When I give it gas (mainly when its cool outside) it sounds like a nut stuck in the exhaust, or a bad cv joint (if it had one =P). During the day it won't be as loud as during the evening hours. I thought it was the flywheel being too close to the starter (which I fixed) but the problem still persists.
This problem just arose last week. Performance isn't effected. Could it possibly be something to do with the driveshaft or u-joints? I got under the car in drive and noticed that the sound came from the flywheel area. Could it be the yolk or something flying around in the tranny pan? Sound is not consistant, it's irratic. The sound will not happen in park, only in gear.

Try checking to see if all of the torque converter bolts are tight. If I have one loosen up, I get a sound similar to the one I think you are trying to describe.

Ok, i'll try that when I get it home. Hopefully it's not a stray bolt playing around in the tranny pan. I did notice something with my exhaust, the previous owner did a "home made" job. A friend of mine noticed that this job wasn't done by professionals. Alot of welding jobs. Anywho, he was talking about inside the muffler of a screen of some sort that, depending on the temp inside the muffler, would cause it to move around? Any thoughts on that?

Thanks again steve for the reply. http://www.nastyz28.com/ubb/wink.gif

Well, I bolted down the torque converter, but it still makes that sound. I was checking out the tranny bolts on the drivers side and they were pretty loose. I bolted down anything that had a bolt on it within reach cause at this point, it could be anything.

My friend said it could be the torque converter, but i'm not sure what it does. Can someone explain what it does? I'd like to understand the concept of it all http://www.nastyz28.com/ubb/smile.gif