Knocking sound at low rpm (video attached)
 

Hello everyone. I have Porsche 911sc 1979 sportomatic.

I’ve noticed a knocking sound coming from my engine when the RPMs are low. It doesn’t seem to happen at higher speeds, but at revs, the noise is quite noticeable.

Does anyone have an idea of what could be causing this?

Here’s a link to a video where you can hear the sound:

[https://youtu.be/zuZhG0kmnw8?si=afWaFWJs27MMgn60]

Thanks in advance for any help!

Did this develop suddenly? It does sound like a valve adjustment is needed. Many threads on this subject. Also, when you pull the covers make sure all the rocker arm shafts are fully engaged.

Vid is too short, hard to tell. But be careful cause if it's a chain tensioner, all hell can break loose.

it is not the valve adjustment, it is not the chain tensioner,
You should drain the oil and see if there is any debris on the drain plug .
Also more info would help...the rpm is too low-why ....and also sounds like a rod noise..
Do you hear it when cold only or hot as well?
Ivan

^^This. Way too solid/beefy/low pitch for a valve issue. It's a solid sound that would lead me to rod, loose flywheel, or something much larger/solid.

I wouldn't drive that anymore.

Crank it by hand, check if there's a similar sound.

Remove the bumper if you need to.