4W4K3

Hey guys,

I've noticed this strange rattling noise from the engine when above about 2200 RPMs. It's pretty noticeable in the video. Any ideas on what it may be?

https://youtu.be/VZ9TrIMi-CA

mrgreenjeans

Sounds like rod end bearings on the way out;

I would get it checked out before you ruin the crank. Like no more revving ; actually no more running at all.

How many miles on the engine ? And have the rod brgs. been changed out before ?

4W4K3

Well then, that's terrifying. The engine has 43k miles and the car's spent most of it's in storage. I bought it from the second owner (75 year old lady), and she had purchased it at an estate sale of a deceased local cop. It's honestly in overall excellent condition otherwise and she had only put 2k in her 10 years of owning. I wouldn't expect it to have been romped on by her, but I suppose that's hard to say to for sure.

I have no record of the rods ever being replaced, but it did have recent general servicing when she owned it, no record of the local import shop noticing anything though.

How should I go about personally testing this theory, or can I?

marc abrams

I would have a knowledgeable person listen to the engine in person. Smartphone audio for recording engine sounds makes every car's engine sounds like they are ready to explode.

StoogeMoe

That's definitely not rod bearings. Something is loose and rattling. Can you narrow down where the sound is coming from?

4W4K3

I will dig in deeper and look for an external source of the rattling. Is there anything in the general area of the central engine region known to come loose? Heat shields and such? It's definitely a metallic sound.

I previously had an early Audi TT with a cam chain tensioner that was failing. Just for reference the noise *almost* sounds like a much more subdued version of that, especially since it is consistent with the RPMs.

mrgreenjeans

If you go to You Tube and search this, you will find dozens of videos of various states of rod bearings making many various sounds on their way out. From loud whump whump whump and metallic clanging to softly sounding noises like it's coming from the valve train, to sounds similar to the bearings going bad on the sides of the engine from the balance shafts failing.

I have heard several at the track with this EXACT same noise and when the pan was pulled, #2 rod bearing was shelled.
This happens from dirty oil. From oil pumps not pumping correct pressure. From low oil pressure from stuck oprv (oil pressure relief valves).
The rod bearings are considered a NORMAL maint. item at around the 150,000 mile mark OR less. Sometimes more. The number 2 bearing is somewhat shrouded by the oil pump pickup assy. in the pan and somewhat vulnerable to not getting the same oil splash as the others. IF the car was ever autocrossed, possibly with a cheaper low quality or dirty oil and had long sweeping turns which caused the oil to scavenge and suck dry, this can happen in just a few short laps. I saw it happen with a car with around 5,000 miles using Castrol 10/30 oil back when these cars were new.

And, Porsche DID NOT stand by that warranty. He spent around 10 grand for a new engine.

My first thought if this ISN'T rod bearings, it is possibly from the balance shaft bearings, but these rarely ever fail. You can take an oil sample and have it analyzed for bearing material by reputable companies which do this service. Heavy equipment owners and operators live by this for their machines, catching issues before they become expensive or terminal. Same with over the road trucking companies. Sports car racers, drag racers, or just plain hobbyist/enthusiasts who are super attentive to their car engines. The read out on the sample will be back to you in a few days and tell you by their analysis if there is bearing material shedding off into the oil.

Is it currently using a quality 15/50 or 15/40 weight oil ? If this car is living in a hot climate and using a thin oil, then failure is definitely in the mix. The Owner's Manual has a great chart in it delineating what weight oils should be used and at what ambient temps.

And rod bearings are not the end of the world. UNLESS you have turned a bearing and ruined the crank. Cranks are getting a bit expensive and harder to find sourced without problems. Bearings are cheap if standard sizing and the biggest expense will be for the labor changing them out.

4W4K3

Thanks for all the info mrgreenjeans. Like I said in the previous post, the engine has 43k miles on it and I honestly would have a hard time believing it was ever really abused, considering the history I have on it and the general condition of everything else. But yes, the little old lady could have secretly been in the SCCA...

In all seriousness though, I'm running Valvoline 20w-50 VR1 and the P.O. regularly had Napa branded 15w-40 changed in it. I'm certainly not ruling out the rods, especially if you have heard this sound before. But I really have no indication that anything was abused aside from the neglect of it sitting in a barn.

As for climate, I'm in northern Ohio and it's generally warm in the summer and cool in the winter, but not too extreme in either regard.

4W4K3

Quick update guys; I've watched just about every video I could find related to 944 rod/bearing knock and I don't think my rattling noise is the same as those. They were all much more pronounced and severe sounding.

Maybe this noise could be early stages of that, but now I'm hunting for any loose bits that could be rattling outside the engine. Still haven't found anything though. I'm going to get under the car and check the exhaust manifold and mounts next.

Just an idea, but does this sound like it could be coming from the cam chain tensioner?

4W4K3

Good news, I found the source of the rattling. It was the clamp on the component shown in the pictures, the nut was touching the top of the engine. So now the question is, what is this piece? It's something to do with the coolant system, and has an electronic connector on the back side, closest to the firewall.

kyle a. w.

That's the idle control valve. Part of your vacuum system.

4W4K3

Ah ok, so that was a vacuum line and not a coolant line. I'll try to reposition it to avoid the rattle. Thanks for the help everyone, glad this was something simple.

jhowell371

A loose O2 sensor drove me nuts for a while. I kept looking for a loose heat shield. Didn't find out until my S2 started running crappy so I checked the O2 sensor. It was loose, when I tightened it up the car ran perfectly and the annoying rattle was gone

RJ80

I've found that some people here are very quick to diagnose bearing noise (rod, crank, balance shaft, etc) for some reason. Almost every time the true cause ends up being something far less serious. I've had it happen to me a couple times. If you do a forum search, you'll typically find the same results.

That's not to say strange noises shouldn't be treated cautiously, but most cars that are driven in normal (non-track/competitive) conditions and have been well maintained simply do not face these catastrophic issues with any frequency.

divil

BTW there's no cam chain tensioner in the 8v engine. There's only 1 cam and it's driven by the timing belt. Glad the noise turned out to be harmless though