1980 911sc weird engine sound
 

Hello, I've had this 911sc for a few months now and noticing this weird clunking kind of sound that gets a little better after warmup, I recently changed the alternator and did an oil change. Seems to also get quieter when I press in the clutch. Any input on what would be causing this sound?

https://photos.app.goo.gl/RPax1qHBksHtvrrc7

I'd start by pulling the valve covers and check for broken valve springs, rocker shaft position and broken head studs. If everything checks good adjust the valves and put it back together. I wouldn't be driving it.

The best would be if you can get the car in the air,either hoist or jack stand-safety 1st thou.After use stethoscope or screwdriver (one end to the location the other end in you fist and to your ear) to locate where ths noise is scoming from. Could be around the clutch..Yes it is internal as Walt said i would not drive it at all

Ivan

First thing to try; remove the fan belt, run the car for a short time [ no more than a minute or so] just to make sure its nothing to do with the fan, Belt, or alternator.
Ant.

The video is a little shaky on its own (in future: hold it still for a bit) but your engine seems to be moving more than usual.

Makes me suspect the engine or trans mounts, especially given you indicate it’s less bad with the clutch in.

Ant’s advice / checking that the alternator, fan & pulley are secure is also good.

Thank you guys, I'll spend some time to check these things out and report back!

If, as you say, putting the clutch in reduces the sound, then it's possibly the throwout bearing. They can rattle when not engaged. (If it rattles when engaged, then it's time for a new one.)

That said, that's a bit more chunky of a clunk for a TO bearing. Time to bring out the long screwdriver to probe around for the source.

The surging is probably a lean condition or one of the regulating items is cycling when it shouldn't be.

Perhaps the O2 relay has gone out.

ok guys this in not oxy sensor or alternator stuf not even the valve adjustment.It is an internal knock ..could be serious since we have no info about the car.The knock could be rod bearings ,loose pressure plate even transmission..since it goes away with depressing clutch .we need more sounds investigation from the OP..everything else is is just wild guessing;-)

Ivan

Does this sound similar ?

An oldie but goodie from one of our very own !
<iframe width="519" height="389" src="https://www.youtube.com/embed/5tdpCYyvqSc" title="MVI 3723" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe>
https://forums.pelicanparts.com/porsche-911-technical-forum/683446-1980-911sc-suddenly-running-rough-any-ideas-2.html#post6816443

I think all who have posted so far are aware of the seriousness of what it could be Ivan, just making sure the simple stuff has been checked before going further into it, for a start, the motor is running pretty erratic on idle which is not a good start for assessing things, as this alone can cause a notching effect on the crank and timing gear clutch etc.
Lets see what the OP comes back with.
Ant.

this is totaly different problem and sound as well....
The OP has a knock......his secondary is the runing which can be sold after.
Ivan

I’m here with ant7 and Ivan.
The more information Ben provides, the better the diagnosis will be.
A good approach would be to get the engine running properly first. To me, it sounds like it’s idling at a very low RPM, sputtering, and running lean — or maybe the ignition isn’t working correctly.
Once the engine is running smoothly, I’m sure it will sound much more natural.

I haven't gotten to check my car yet but I can say regarding the idle surging that happens when it's cold and then once it's warm it idles smoothly.

Ok, then also check the cold (and warm) control pressure of your WUR to make sure they’re within spec.

It would be interesting to see a video of the engine when it’s warm and idling smoothly, to hear how it sounds then.

he most likely does not have any testing fuel gauges ..but try to increse the idle with this screw
here is how
https://forums.pelicanparts.com/porsche-911-technical-forum/103004-wheres-idle-screw.html

He should get one, as these are quite affordable, or have a service garage perform the pressure checks. I think that’s a must, at least if it has never been done on that car.
If it’s running significantly too lean, as it might be in the video, it will still run rough, even at higher idle RPM.

true if the OP is a little mechanicaly skilled To check it at the shop would have to be towed ..and it would have to be 911 service people to start with.
I would as i said 1st ,look for the noise a locate it....lift it up a search the best with videos so we can help

Ivan