Diagnosing a new engine noise

[mnez]

The engine in my 86 911 recently developed an unusual tapping noise. It is most noticeable at idle, and is not very loud. It is a rhythmic tapping that does not get louder with higher rpm. I cannot hear it in the car at anything faster than idle.
I have not been able to localize to the left or right side yet.
The car has done several hundred miles since first noticed, with no change in the sound, and no perceptible loss in performance or drivability.

In the video, it can be heard as a faint tapping buried under all the normal engine noise.

Can anyone tell if it is at crankshaft speed or camshaft speed (idle is 900rpm)?
Any thoughts on the source?

https://youtu.be/w7s1KFU4ZLE

[proporsche]

it does not sounds like any danger..most likely you valve adjustment is a little off

Ivan
what was the last time it was done?

[mnez]

Valve lash was set 9000 miles ago.

Although the noise is quiet, it is reasonably new. First noticed it September, but it could be older since its not super obvious.

One other thing - it's not noticeable when the engine is cold, only when it's hot.

[proporsche]

well..9k could be easily by now out of adjustment-when the engine gets war-hot the gap is larger

Ivan
the best would be if you can make a video a go around the engine with the lid up...

[tshebib]

Hey Mike,
Are you still tracking the car?
As you know, 9000k with track miles equates to more.
Back in 2011 my 3.0 started with a slight odd noise similar to yours. Turned out to be a broken head stud. That put me down the slippery slope of the 3.6 transplant. Although in your case that 3.4 is no slouch. Hopefully it's just valve adjustment time. Either way, you'll find out quick enough when you pull the valve covers.
Hope all is well in your neck of the woods. We've been pretty lucky down hear in Nova Scotia with Covid (well at least so far).
Cheers, Tom

[mnez]

Hey Tom, good to hear from you.
Yeah, still tracking it quite a bit, especially later in the season when the tracks opened but we couldn't instruct, so quite a few open track days.
Things have been very good where I live, not close to any hot spots, and we're not really on the road to anywhere. You guys will need to make a road trip this way next summer (with luck).

The next several days are forecast to be quite a bit above freezing, so hoping to get the motor good and hot, and poke around with the stethoscope before pulling covers.

I'll post a go around the engine video if there is something to hear.

I've been down that slope...

[Konrad Sauer]

Hey Mike,
Following this thread with interest as I have a similar sound coming from my 81 SC. Going to be doing a valve check/adjustment shortly to see if that resolves it. Curious if your valve adjustment got rid of the sound in your car.
cheers,
konrad

[mnez]

Konrad, too early to say. It was only noticeable when the engine was fully hot after being on track, so can't say until back on track. Hopefully in June.
Some valve clearances were a bit loose, so maybe.

[Konrad Sauer]

fingers crossed the loose valves were the issue.
cheers,
konrad

[ahh911]

Gosh, that's a quiet sounding engine, I don't hear anything that would alarm me. My 81 is quiet until it warms up then the right side starts to make some noise, but if it was as quiet as yours once hot, I'd be very pleased.
Phil

[Dpmulvan]

Get a stethoscope, check cam chain housings and valves.

[mnez]

Follow up.
I did the valve adjustment and after quite a few days on the track I can safely say the sound is gone, so I guess it was the valve clearances after all.
A good win.