Could this be a rod bearing?

[jderimig]

The description of the noise

1. No noise when cold (oil pressure > 4bar)
2. Start to hear it when oil pressure at 3bar.
3. No pulsing of the oil gauge.
4. Oil pressure stays 3 or above at idle, running 20W-50 oil.
5. Noise is very subtle hollow tap, probably cannot hear it with hood closed, but I have become paranoid-ally sensitive to knocking sounds. I doubt my cell phone recording could pick it up but I will try that later.

Troubleshooting so far:
1. With stethoscope sound seems to be coming from cylinder 1, I hear it about the same loudness whether I put the stet rod on top of the head or the oil pan. I can hear it in both places but one doesn't dominate over the other.
2. Listening with timing light flashing seems to timing with crank not valves.
3. The noise goes away when I pull off the #1 spark plug wire.

Car information:
84 NA
~50K miles
one DE 30 years ago
Not driven hard but had a 0 oil pressure incident from crankwasher backwards when changing belts about 1000 miles ago.
Noise could have always been there, I am just sensitive to these things now.

[944 Ecology]

Could be a rod bearing (although #2 is the more likely candidate for a rod bearing) or a wrist pin.

Drain the oil into a spotlessly clean pan and look for metal from the rod bearing. Also check the magnet in the drain plug.

[jderimig]

I cut open my filter and there was nothing I could see in the elements (but there was only 130 miles on the filter). During the last oil change there was magnetic sludge on the magnet but no flakes or larger pieces that I could feel with my finger.

I am slowly resigning myself that I will be pulling the oil pan eventually.

[JD159]

Does it happen when cold? Or just hot? I'm suspecting lifter bleeding out when the oil is hot.

Is it chipped?? Any chance it's pinging? I had that on my S with the chip.

[jderimig]

Just when hot. Listening with the noise along with a timing light seems to indicate its a once per crank rev noise. No chip and doesn't "sound" like a ping.

But running some ATF or Seafoam in the oil to see what happens is a cheap test.

[JD159]

Originally Posted by jderimig

Just when hot. Listening with the noise along with a timing light seems to indicate its a once per crank rev noise. No chip and doesn't "sound" like a ping.

But running some ATF or Seafoam in the oil to see what happens is a cheap test.

Could you swap the injectors around? See if the noise changes with the injector.

[jderimig]

The noise goes away when I disconnect sparkplug on cylinder 1. I am thinking injectors wouldn't care. Not sure if valve noises would care either.

[SReppel]

Do you have oil analysis done for you car? It's cheap insurance and recently saved me from wiping out my 944 track cars engine.

Sent in a sample and had higher levels of copper and lead than the last sample.
Even though I had good oil pressure etc. I did not want to chance so changed out the rod bearings. They all had wear, not significant though.
The #2 bearing is usually the culprit but strangely the #4 had the most wear.

I use BlackStone Labs for both of my cars and send a sample in ever time I change oil.

[jderimig]

Haven't done so yet and should have done it with the last oil change. I have the BlackStone bottle ready for the analysis but only about 150 miles on the oil. Is that enough time to detect any metal in the oil?

[djnolan]

Call Blackstone and ask and also read their FAQ. They see this stuff every day. just as likely you have an ignition or fuel issue.

[SReppel]

Originally Posted by jderimig

I have the BlackStone bottle ready for the analysis but only about 150 miles on the oil. Is that enough time to detect any metal in the oil?

Mileage doesn't matter for determining if there is any higher than normal levels of indicator metals such as copper or lead.

I've looked at many bearing failures and other components over the years since I was the Lead Reliability Engineering person doing root cause failure analysis on equipment for a major oil company.
Oil analysis was one of our predictive maintenance tools. I'm a firm believer in it.

You may have another problem but this would eliminate any rod or crank bearing problems.

[jderimig]

Thanks, well I definitely will start doing that. I emailed the folks at BS and they say although they prefer more miles on the oil if there was a bearing problem there would be enough metal in the residual oil from the last change to detect a possible issue. So I pulled a sample last night.

However I am probably going to pull the oil pan anyways and have a look see. I ran some Seafoam last night and there was no change in the sound, a definite developing thump from #1. So I expect some clearance in the system somewhere.

Another question, is is possible that a previous lubrication problem wore some clearance in the bearing but then stopped leaving a clearance without additional wear? Or is it once you develop clearance the wear continues to progress? In other words is it possible to get an oil analysis with little or normal metal in it but still have worn bearings?

[JD159]

If your oil pressure is good, and the knock is barely audible, I'm really thinking this is not a rod bearing. I think you would just know if it's a rod bearing. I just changed mine at 120k and they were barely worn. They are fairly robust. Furthermore, temperature shouldn't be a factor in a thrown bearing.

[SReppel]

From what you have said so far, it does sound like a rod bearing knock, but it seems like your oil pressure is holding steady. Once it does start to get more clearance the rod will start knocking on every compression stroke especially at higher RPM's leading to failure.

It could result in a rod through the block as I have seem happen to one of my friends at the track.

Sounds can be misleading sometimes and hard to diagnose where they are coming from.

All bearing wear over time gradually even with proper lubrication. We use to pull a few bearing to check them on our large compressors when doing annual inspections just to validate their condition.

You could get back good oil analysis results and then get a bearing failure due to detonation or something like an oil pump failure.

I think you are doing the right thing by removing the pan and checking the bearings. It's not that bad a job, having recently done mine.

[jderimig]

Originally Posted by JD159

If your oil pressure is good, and the knock is barely audible, I'm really thinking this is not a rod bearing. I think you would just know if it's a rod bearing. I just changed mine at 120k and they were barely worn. They are fairly robust. Furthermore, temperature shouldn't be a factor in a thrown bearing.

I am with you but I am still a little nervous. The stethoscope isolates pretty well and it sure seems to emanating from cylinder 1. The other thought is wrist pin noise but those are not pressure fed with oil so I was thinking oil viscosity shouldn't matter.

What else could thump?

I'll let you know what I find (or don't find) depending how far I get this weekend.

[jderimig]

While I am there question:

Will the factory turbo (late) oil pan baffles fit an early (84) oil pan?

[djnolan]

Well get the oil analysis done first. Then consider if it is an injector or ICV making the noise, maybe? Or a belt roller or water pump bearing since it is up front on the engine? (not to mention spark knock) Have you tried higher octane fuel? Is it a loose injector harness plug causing lean mixture and knock.

(believe me I have been there with funny noises on these engines)

[jderimig]

Originally Posted by djnolan

Well get the oil analysis done first. Then consider if it is an injector or ICV making the noise, maybe? Or a belt roller or water pump bearing since it is up front on the engine? (not to mention spark knock) Have you tried higher octane fuel? Is it a loose injector harness plug causing lean mixture and knock.

(believe me I have been there with funny noises on these engines)

Good advice. Its running 93 octane now.

I have stuck that stethoscope rod everywhere (well almost everywhere) including the waterpump, ps pump, ac pump, injectors, cam tower, timing belt cover crankcase at the oil pump trying to track it down and only hear it at the top of the head and oil pan.

[jderimig]

Here a pic of the rod bearings from cylinder 1 (just pulled) them.

For the experts out there do these show unusual wear?

[JD159]

Originally Posted by jderimig

Here a pic of the rod bearings from cylinder 1 (just pulled) them.

For the experts out there do these show unusual wear?

Enough to cause a knocking??? I doubt think so. But others will hopefully chime in.