What does this noise sound like?

[gmcman]

2004 TB 4.2, 200K miles, religious oil changes at 5-6K with Mobil-1.

I was helping a buddy with the stepper motors and heard a light tap, owner was unaware and if you stand in front you can't hear it

Obviously with the recording being a few inches from the bell housing, it's very audible. Had light glitter in oil, and I can't tell if it's a rod or pin. Nothing overly telling on the stethoscope around the pan or side of block.

Here's the video:

I pulled the pan and only have removed the #5 &6 caps, had to finish up early. With an oily surface, (not cleaned) I have
0018" clearance, maybe .0019 if cleaned up. #5 journal looks brand new, #6 had very light marks but nothing you can feel.

The knock is roughly 5-6 Hz, but hard to tell if it's a double-tap from a pin, also a little deep for a pin.

Could this be the very beginning of a rod bearing failure?

Here's the #6 journal



#6 lower bearing



The bearing looks ok, but when do these motors start to have an audible knock? Since max spec is .0025'

I still need to pull 1-4, but what's odd is the noise is from the bell housing area. Converter bolts are tight, and I can't see any cracks in the flexplate.

Open to all thoughts.

 

[azswiss]

Sure sounds like a cracked flex plate.

 

[gmcman]

Sure sounds like a cracked flex plate.

I will get in there with a endoscope camera and look again. I was concerned with the noise coming from the bell housing but could not see any cracks.

Here's a vid with the inspection cover removed.

 

[Mooseman]

Rod knock. And having forbidden glitter in the oil confirms it. Open the oil filter to check for even more glitter. Can also check the CPAS screens. The glitter would have circulated all over the place ruining the other bearings, the oil pump and cam saddles/caps. That one bearing you show has evidence of that although it's not the failing bearing. It may be just at the beginning of failure but it will go downhill quick from there.

Flexplate would be more irregular and tinny.

 

[gmcman]

Open the oil filter to check for even more glitter

I will cut the filter today and post some pics.

 

[gmcman]

I cut the filter, now scratching my head.

First, here's the oil we drained with about 2000 miles on it, clearly there was silver and some gold/bronze color specks.










However the filter is clean, maybe a speck or 2 of silver.



The sound is too rhythmic to be a flex plate and if so, would be faster wouldn't it?

The last few oil changes were done with the nose in the air so maybe the particles didn't fall to the sump until now...possibly skirt wear over time.

I may need to scrape in the media to find the metal but generally wouldn't it be readily visible?

 

[Mooseman]

Skirt wear would have been silver only. Bronze/copper coloured specs would be copper from the bearings.

Is this a new filter from when you changed the oil? Might just be that it hasn't had enough time to collect more bits or maybe you can't see it because it's super fine and brown? Maybe try and rinse it with brake cleaner into a clean white bowl. Anything metallic coloured is not good but check if it's magnetic in case it's iron from the rings/cylinders.

If the motor still has the oil pan off, I'd be checking the other rod bearings. Mains would be a PITA with the saddle to remove. The regular knocking noise would indicate a rod bearing.

 

[mrrsm]

In a related thread...

Dreaded Knocking Noise 2008 GMC Envoy 4.2L I6 220k miles

The other day I just crested over 220k miles and heard a small knock when on the highway. Parked it at home and have yet to start tearing into anything. I'm pretty good at most repairs on vehicles just unsure if this will result in the engine having to be pulled. Any help would be greatly...

gmtnation.com

...these images show the portions of the GM Factory OEM Bi-Metal Aluminum Silicate Thrust Bearings fitted at Mains 5th Position, nested inside of the Upper Block narrow buttress cut-out and highlighted in these images that can also become the source of those Metal Particles during break down:




If this is so... the Fore and Aft hunting of the Crankshaft --might-- also encourage the Flex Plate to Crack from the excessive in and out Flexing of the Torque Converter longitudinal motions... and may also be accompanied with a P1345 Code. There is a GM TSB describing this issue... and the contamination of the Oil Galleries with Metal Shavings that can come as the result.

Note that the destruction of these Bearing Side Plates (TIG Welded at 3 places per side) would NOT necessarily cause the particles to wind up being captured inside of the Oil Filter ...since they can be flushed away by Oil Under Pressure leaving the Bearings and then slung away by the centrifugal force of the rotating Crankshaft... and then wind up floating-sinking into the bottom of the Oil Pan.

Any Bronze-Copper looking metal discovered would have to come from the Thin Ends where the Connecting Rods encircle the Upper Pin Boss of each Piston due to the placement of Press Fit Bronze Bushings inside of the Rod Ends.

 

[Beacon]

Maybe take an oil sample and send it in, at least you would know exactly what metals are showing up, although it seems to takes several weeks to get one back. However, I seem to have read that sending the sample to blackstone in a box from the post office, or your own speeds up the process, rather than using the mailing bag that blackstone sends you

 

[mrrsm]

Precisely... The GM (OEM) Mahle - Clevite (Mains) Bearings ratios-percentages of Aluminum to Silicate (AlSi) blended into their wear resistant Bi-Metal Alloys are well documented, including the technical aspects and modes (appearance) of Bearing Failure are available at the Mahle Main Products Page and can help to inform and confirm whatever the Blackstone Oil Analysis comes back with to "Pin-Point The Problem Parts" via this PDF.

https://www.mahle-aftermarket.com/media/local-media-north-america/pdfs-&-thumbnails/catalogs-and-literature/engine-bearings/eb-20-18.pdf

 

[santon]

I had similar noise for about 2 years, since I bought my 2005 TB. The noise was noticeable at all gears and usually became louder after some driving (i.e., when the transmission was hot). The noise was not so related to the engine RPM. I checked with the stethoscope, the noise was originating from the bellhousing. I even disconnected the torque converter from the flexplate for test. When I did that, the noise disappeared. The flexplate was not cracked. Also, I had noticeable vibrations at highway speed, and these vibrations were well correlated to the locking/unlocking of the torque converter (I used Torque application to observe the TCC slip during driving). There were no error codes (P1870, etc). So, although I also suspected the rod knock, my diagnosis was the bad torque converter. Finally, today the torque converter was replaced - and the noise and the vibrations disappeared! The truck runs smooth and quiet. As I said, it took me 2 years to understand the problem and fix it. So, if the noise is coming from the bellhousing, I would suggest disconecting the TC from the flexplate and see what happens.

 

[gmcman]

I would suggest disconecting the TC from the flexplate and see what happens

Sorry for the late reply, that was going to be the next step if the rod bearings did not fully fix this issue. With glitter in the oil I had to tackle that as well...also the very rhythmic knock that happened at any speed regardless of being in gear or not.

So late update, I didn't get to plastigage all the bearings, with the brace in the way I wanted to check each journal in 2 different spots but only had time for # 5&6. I forgot to clean the surfaces and was right about .0019-.0020 so the readings weren't accurate. Not a good feeling as that's still in spec.

Anyway, we changed out all 6 bearings, new pickup tube seal, new bolts and with it all back together, it sounds much better.

Looks like #5&6 had the most visible wear, but not terrible. I will mic each bearing and get a pic of all of them shortly.

 

[mrrsm]

Just an FYI.... Since both the Connecting Rod Fasteners AND the Cradle-Mains Fasteners -=are=- of the TTY Flavor... Here are some Factory OEM Images with their Part Numbers... should you need to get your hands on them again:

Connecting Rod TTY Fasteners



Steel Support - Mains Cradle TTY Fasteners:




...and a bit of "Cradle-Mains" Trivia that might come in handy some day for Crankshaft Clean-Up and Journal Dressing. Note the need for (14) Fastener Replacement Positions on this inverted item: