Hurdigurdiman

ON a cold start as I fire the car up I hear what sounds like a chain slap against metal. Only for one second no more. Is this something I need to be worried about. Any explanation as to what/why this is would be well appreciated. This has been happening since I got the car almost 3 years ago and it has not gone any worse. I know I am not on my own on this situation but I would like someone to explain, what it is and can it go worse. What could be the consequences down the road? If any.

Imo000

My buddy's does this too, it has to be the chain tensioner/s loosening when the oil pressure is gone. With a stetoscope try to find which one is making the noise (might take a couple of days) and replace it. That's what we'll be doing.

Macster

All the tensioners allow the rail to retract a bit as soon as the engine is shut off and oil pressure drops to zero. The tensioners might retain a bit of oil pressure for a while -- a short while (moments, make that a moment) --and with the engine off there may not be much pressure against the chain rail which would work to force oil of the tensioner piston but the tensioners will lose oil pressure sooner rather than later and there'll be a moment, half a moment, when the chain will have a bit of slack upon the next engine start.

The 1st second the engine is not even up to its idle speed... cranking speed is IIRC around 75rpms -- so there's a bit of cam chain slack and a bit of noise. All the real chain force is on the tight side the side that is pulled tight as it spins the cams. The tensioner is on the back side and really only deals with the chain's, well, slack which has no real pressure.

Unless you find bits of composite plastic material (chain rail covering) in the filter housing oil and in the filter element or you hear this chain slap after the engine is up to its idle speed, my layman's opinion is there's nothing to worry about.

However, for your peace of mind you are welcome to run this by your trusted tech for his input. Have him give a listen under circumstances during which the noise is most pronounced.

On a related note I hear noises when I start my Boxster's engine (and my Turbo's engine). But as long as the noises go away right after the engine starts -- and they do -- and I do not hear them after the engine is running -- I don't -- I don't pay them any mind. And this applies to when the car was new and the other day when I started the Turbo engine with 112K miles on it, and the Boxster engine with nearly 273K miles on it.

Dennis C

Sometimes I hear a noise when I first start my C4S too. It typically only happens on very cold days when the car has been sitting for a while. It almost sounds like a slipping belt for just a second. It has done this as long as I have owned it and it always goes away immediately after the engine starts. I'm wondering if this is the same noise you're hearing. Mine sounds more like a "screech" and less like a chain or chain slap.

Macster

How old is the serpentine belt? Check its edges for wear (sharpness). Check the ribs for any missing sections.

Dennis C

It's not old, but I'll check it.

5CHN3LL

Chain rattle on startup is a known complaint for mark I 996's...

Topaz330ci

Mine does the same. The screech when it's colder, and the somewhat of a rattle when it's not as cold. The screech is only on the first cold start, and the rattle is once in a while.

I haven't seen it progress, and my car is in tip top shape in regards to engine maintenance.

2003 C4S with a Porsche warrantied engine.

Hurdigurdiman

Belt is good. I put a new one on it about 18 months back. It only slaps for a second after a few days in the garage on the first start. Never hear it when I use it daily which I normally do. From all your remarks I have nothing to worry about. Every 5000 oil and filter change I cut open the filter and it's been clean and I mean really clean. I have done about 6 oil changes in the last 2 years. Since I changed the plugs and sleeves in the past couple of days this car has taken off. I mean I though it was a mover before, but now OMG who the hell needs a turbo when these things lift off and accelerate like they do. They are awesome engines and the handling is something else. Even the sound is more growly on hard acceleration. The car is sharper than a Gillette blade.

5CHN3LL

One of the goals of the IMS redesign for (I believe) MY01 was to address drive chain tension to address this issue. Our '99s rattle more than later 996 model years...

dmw996

Hurdigurdiman - My 2001 C2 displays this 'feature' as well. One way to narrow it down is to pull the fuel pump fuse on a cold engine, turn her over for 10-12 seconds, push the fuse back in, and then try it. Mine cranks quietly after doing this but rattles 4 a 1 sec @ crankup after sitting 4-6 hours otherwise. I am replacing my IMS and 1-3 tensioner as well as swapping to 5w-40 Motul Xcess this weekend to see if I can make things any better.

Also, concerning the other mentioned 'shrieking' sound, if mine sits too long, sometimes the starter gear fails to retract on crankup and gives some unwanted noises. Thankfully it has stopped that as of late.

pszikla

Hurdigurdiman!
I found the exact same things when i changed out my plugs end of August before the big road trip.
What a difference, it was really noticeable!
For the record, mine has been chain slapping for 5 years now, no worse today and the noise stops the second she is running.
Pete

5CHN3LL

Yup, I have this too. I'll get around to replacing the starter eventually.

5CHN3LL

Starter for a '99 996 is Bosch SR0808 @ Amazon for $155, BTW.

alpine003

KK would pat you on the back and possibly even give you a eHug since you recently did a DIY as well.