Help me identify this engine noise..
 

1970 911t, engine rebuild about 6 years ago. Just last week this rhythmic sort of rubbing engine sound started. There at idle and increases with revs. No change in performance. Coming from fan area so assumed it was the fan rubbing on the housing. Removed the pulley and belt and fan seems to spin fine. No cracks on shroud. Can alternator make this sound? Any other areas to look? Hope the video helps. Thanks.


https://youtube.com/shorts/xJYv4shA4_Y?feature=share

Run the engine for a short time [30 seconds] without the belt to rule out a problem with the fan etc.

Almost sounds like you have a spark plug that is loose...

Agree that it sounds like a compression leak.

After listening to it again, It does sound like a loose spark plug, or maybe [hopefully not] snapped head studs ?

did the 1970 911T have the smog pump ports on all the cylinder heads? if they were "plugged", perhaps one plug has rattled out. Would be the same noise as a loose spark plug.

Great advice.

I'll run the engine briefly with the belt off.
I can try to check if any of the spark plugs are loose assuming noise continues after belt off.
I'm not sure about the smog pump. I don't think so. Pulley only has one groove for one belt but regardless I'll look into that too.

I think the cadence of the noise rules out the fan. Sounds like a rocker, or compression leak, possible broken head stud ( ?) Difficult to determine based on the audio.

I think smog pumps ( air pump) were on the later models, beginning in '74 . Could be mistaken.
I would check compression on all cylinders as a starting point.

Sounds more mechanical to me. I'd start by removing the valve covers and check head studs and rockers. Do a valve adjustment while you're in there.

Ok. For what its worth when driving at speed its less noticeable but maybe thats just a frequency thing.

Just a note. If you decide to do the valve adjustment, this must be done with the engine stone cold.
In case you didn't already know.
Hope this helps.

The 1970 models did not have the thermal reactor fittings, but in 50+ years, you don't know what a PO might have done to the engine. It does sound like when my car, with a 1980 RoW engine, lost one of those plugs.

Ran without the belt. Definitely not the fan.
Don’t have the toolkit so I’ll order the spark plug socket and check that next.
If not that then move onwards and remove valve covers.. And just did oil change…
Hope I can figure this out before Fall driving season is over. Just got the wheels tires and suspension sorted out too.

nhs15: If you don't have the toolkit that came with the car, try to replicate one (without spending $1500!). The spark plug tool that came in any of the 911 kits is exactly the right length to reach the plugs past the sides of the engine bay, and it is knurled on the outer end to that it's easy for you to grab and spin with your thumb and fingers.

bump, back to the top

yup sounds that to me too

Ivan

Well the spark plugs all seemed tight. Valve adjustment next?

interesting..can you make another video from the front of the engine and moving slowly side to side..or even from the bottom? How about loose heads?It really sounds like puffing..
Ivan

https://youtube.com/shorts/dkzO3Rn23TU?feature=share

https://youtube.com/shorts/TS0mNsOdXpQ?feature=share

https://youtu.be/-DukRGWVD30

https://youtu.be/4l2zDb7pA6E