Engine Flapping Noise 911sc

[kris159357]

I was driving today and then just suddenly under acceleration there was a loud flapping noise from the motor. It sounded like a playing card on a bicycle wheel.

From the reading I've done it sounds like the dreaded head studs. I jacked the car up to have a look but there is no leaking around the cylinder heads as I've seen described previously. If it were a head stud would there definitely be leaking?

Is there a process of elimination I can check for exhaust problems before taking off the valve covers?

Thanks Kris

[arry911]

I had this sort of noise, turn the engine by hand and see if it turns freely. Mine did not and it turned out I had a blockage in my oil spray bar and my camshaft was not getting any oil over #6 right rear of engine I hope yours is just blowing from the exhaust.

[twistoffat]

Check to see if your fan is loose or rubbing against the housing

[Flat6pac]

Or dropping a chain tensioner..
Bruce

[john walker's workshop]

broken head stud? remove the lower covers and see if there's part of a stud in there. oil out first.

[Josh D]

You can jack up one side of the car at a time to remove valve covers to check for broken studs without draining oil.

[kris159357]

Thanks guys I'll have a look

[Tidybuoy]

If you turn the engine (as suggested above), be sure to only turn in the normal running direction. Turning the engine in reverse can cause damage to the chain tensioners. At least, that's what I've read on this board.

[kris159357]

If I take the valve covers off, is there anything I need to do in there to check, or will the studs be noticbly loose / fall out?

Are there any possible exhaust problems I can somehow check first?

[Bob Kontak]

Originally Posted by kris159357

Are there any possible exhaust problems I can somehow check first?

The studs or a nut will fall out when you pull the cover. Just put a 13MM or 1/2 inch socket on the nuts and give them a slight reef - Finger tip pressure on the ratchet - if they are intact. That's all you need to tell the story. 10 ft lbs.

Pull the lowers only. Start on the right side. No real reason why, just where my broken one was. Plus it's easier.

I do remember a distinctly similar noise when I had farted around with my heat exchanger plumbing. I had clapped out motor mounts too. Something hit something and vibrated viciously and it sounded like a machine gun only under heavy acceleration.

I can't remember what I did but I double checked clearances (e.g., oil lines vs the underside aluminum tube fasteners that feed into the heat exchanger) and fiddled with moving stuff around and it never occurred again.

The thing I question (regarding studs) is that Bruce Anderson's Performance Handbook says the heads/cylinders will start the flipping a deck of cards noise after a while. So based on my experience of zero real life situations, I would like to think you would have to have been hearing a mini version of your noise over time.

[kris159357]

Thanks again Bob, that's the strange thing I can't say I have heard anything. Then all of a sudden doing about 60km/hr under moderate acceleration, there it was. It was also at the mechanic in January and again last week, so I'd have thought if there was a mini version of the sound someone would have noticed.

[Bob Kontak]

Originally Posted by kris159357

Thanks again Bob, that's the strange thing I can't say I have heard anything. Then all of a sudden doing about 60km/hr under moderate acceleration, there it was. It was also at the mechanic in January and again last week, so I'd have thought if there was a mini version of the sound someone would have noticed.

To clarify, only under low speed heavy acceleration did I hear the noise I mentioned.

[kris159357]

Interesting, the sound is there at idle too.

Did you have leaking around the cylinder heads visible from under the car?

I dont have any, but if I pull the lower covers will I be able to see all the studs, or just the bottom ones?

[Bob Kontak]

A recent post talked about the 915 (and G-50) making a perfectly ok gravely noise under acceleration in a higher gear under load. I have it on mine but the noise comes through the floor pan, not from around the car. It is not loud either.

[porsche930dude]

could be detonation. i wouldnt say it makes a "flapping" sound more like a clatter but if you suspect it check your timing. back it off some just to see if it goes away

[Bob Kontak]

Originally Posted by kris159357

Interesting, the sound is there at idle too.

Did you have leaking around the cylinder heads visible from under the car?

I dont have any, but if I pull the lower covers will I be able to see all the studs, or just the bottom ones?

I had no leaking.

You need to check the bottom studs. Those are the ones that pop with heat cycling.

I was thinking the same as Porsche930dude but that is a different issue. Put that in your hip pocket for now.

For one hours work, put the studs to bed.

Lift up one side. Deal with some oil splash out and spilling. Parts store sells "oil dry" cat litter stuff 50lb bag that sucks up oil slicks and get on with it. $7, plus or minus.

Flip sides, do it again.

You will see the head stud nuts in the cam tower once the cover is off. You will only see the bottom studs nuts in the cam tower if you are lucky. Meaning if they don't plop into your catch basin things are looking up.

Get under there and get stinky for a wee bit.

Unless, of course, your are skeered of the power of a 13mm socket.

Get to it.

[kris159357]

Thanks Bob, I'm definitely not scared of getting dirty, it sure beats paying someone. I'll order some gaskets and get started on checking it out.

Thanks

[porsche930dude]

check for broken valve springs while youre in there. another far fetched problem but could happen

[Bob Kontak]

Originally Posted by porsche930dude

could be detonation.

Here is another related thread. In the 2nd post the guy says that a broken stud and detonation sound so much alike it's spooky.

What does a broken head stud sound like?

Also Wayne Dempsey says the noise is really heard clearly if you drive next to a wall. Maybe detonation would sound a little more internal?

[TJJSC]

Are all your "air injection" injectors still in place (next to exaust ports)? or alternatively the blocking off plugs for those.
I lost one blocking plug once giving quiet some noise especially under load.