bekks

2000 Carrera. 75k km. Manual.
I had the engine out last winter to replace the timing chain guides, including the tensioners. All summer I've had a metallic noise that I can only hear at idle. I'm fairly certain that before I did the engine work, it didn't make this sound. I've checked all the spark plugs and they're good. I changed the oil pump piston and spring. I took the belt off for a few seconds with no change. Seems a little louder on driver's side (left). In the video, I can hear a higher pitched metallic noise that I can't hear in person, but the sound I'm interested in is the somewhat inconsistent rattling. Any ideas?

Seems my video isn't hyper linked. You'll have to copy and paste. The sound doesn't really start until the end of the video. No metal in the oil filter, but there is some green plastic, which I think is probably my variocam o-ring.

https://youtube.com/shorts/GmQLuNEii9U?si=uXtoMhMwOOhCirOW

sublm8

The sort of intermittent rattle most prominent towards the end of the video? I had a similar sound on my 968 which has a very similar valvetrain. Sounded just like that. Started after variocam pad replacement, only at idle. Took the valve cover off, everything was fine. Had my indy listen to it, his opinion was one lifter was bouncing at idle. As the sound disappeared off idle, the advice was don't worry about it. No real ideas as to why it started after the variocam work. I drove it a couple thousand miles after that with no trouble, and the guy I sold it to also had no issues (at least none he shared with me).

Obviously my experience may not extend to your 996 and I'm sure others will chime in. Did you change the chain or just the variocam pads? Any other changes - like, did you use a lower weight oil in the summer? Can you isolate it with a stethoscope?

Porschetech3

Get a Technicians Stethoscope and listen to the catalytic convertors....

I have had them cause that sound and have even seen people tear down engines needlessly on account of not checking the cats first..

bekks

Yes, the intermittent rattle at the end. Sometimes it turns into a more consistent rhythm. I was thinking it could possibly be a lifter. Same weight oil and original chain - I only changed the variocam pads and larger chain guides. The variocam pads were decently worn.

Stethoscope is ordered. I've been meaning to get one for a long time. I do think the sound is more forward than the catalytic converters, but I will give them a listen.

I actually have the car for sale right now and a potential buyer is scheduling a PPI, so they might diagnose it before I can.

Mike Murphy

I assume that was a cold start? My 996 has been doing this for 6 years now. If I keep revs between 2,000-2,500 RPM and drive off immediately, there is no sound. If I cold start and idle, the sound remains for 1-2 mins and then goes away and stays away.

Could be cats, chain tensioners, piston slap, not sure. I never was able to figure it out myself.

wheelbearing

I have a similar sound more audible from the left/drivers side. Sometimes its there sometimes it is not. Borescope was done through the spark plug holes and nothing was found. Been driving with the car last 3 years and few thousand miles without any symptoms or problems.

bekks

I didn't get much for details on the inspection, but they apparently found some bore scoring, so the sale fell through. I'm keeping it now. I do plan to take the oil pan off and get a good look at the bottom of the cylinders.

I also got a stethoscope and can't believe it took me this long to get one - it's amazingly effective at pinpointing sounds. Unfortunately, I couldn't find the one I'm chasing. I will update when I learn more.

Mike Murphy

Oh, you were trying to sell it? You didn’t mention if the metallic sound is at cold start only or present when the engine is fully warmed up. What kind of scoring did they find?

bekks

The video was just after high idle cold start, however, I believe I've heard the rattle with both hot and cold engines. I don't think I can hear it at high idle, but that may be due to the extra noise.

I didn't get the details of the scoring. The purchaser paid for the inspection and offered to sell it to me for half the price, but I felt like that was throwing away extra money.

Jim Kardas

I had a similar sound on cold startup. Replaced the oil pressure relief valve/spring with the updated version and sound went away. Good Luck!

bekks

I'm back with the same question. I'll be dropping the oil pan soon (to check the cylinders), but wanted to see if anyone has any additional ideas. I took another video, where the sound is much more rhythmic. The sound is independent of engine temperature. I tried putting the stethoscope to my phone's mic, but it didn't pick it up at all. With the stethoscope, I can hear the noise better from the water pump, particularly the clamp on the hose. However, I took the belt off and the noise was the same. There were also a few other, seemingly random bolts that it became louder from. I cannot hear it any louder from the exhaust headers (either bank). This video makes it sound more like bore scoring, but it is still often intermittent.

Mike Murphy

It does sound like bore scoring to me. Didn’t you say a sale fell through because they found some scoring? If yes, that’s probably it.

sublm8

I agree, it sounds different from first video and more like bore scoring.

The prospective purchaser wouldn’t give you the inspection report and wanted you to pay for it? Is that common?