Well, my weird knocking sound in the 2.8 is now gone.

When I first started the motor, it's always been noisy, especially at cold startup. A few knocks until oil pressure came up, and then at higher RPMs (cruising at 70) it was knocking. I bought the motor used from someone who bought the motor used from someone... One of those motors. It did run just fine, and always had good oil pressure. It didn't have a spun bearing rod knock... so I thought it might be saved by a simple bearing replacement (under $13 at AutoZone for all 6). Was a light knock.

So I dropped the oil pan (easy enough, remove starter, loosen exhaust / springs, yank pass side motor mount, jack engine up ~2 inches). Started swapping bearings 1 at a time. Ick, they were pretty bad, but fortunately none had spun, and the crank still looked good (no grooves I could feel). Here's some pictures. Left to right is 1-5, and the second picture is 5-6 and a rod that did have a bearing spin in it (from another motor). That rod is trashed. Bearing material is actually embedded in the rod. I couldn't find the spun bearing, I think I threw it out.

Put the new bearings on dry rods & caps, put a little assembly lube on the bearings, and torqued 'em to 39 ft-lbs (upper range of spec). I did not plastigage, nor did I mic/bore gauge (I have the Mitutoyo tools & plastigage on the shelf, but I just didn't feel like doing it ). The bearings I pulled out were original STD size bearings - marked GM with a date code of late '85. So I went back in with STD size bearings.

Before, my oil pressure was ~20 at hot idle (almost to the red). Now it's a solid 30-35. I've put about 200 miles on the motor since the bearing swap, so (knock on wood) I think I'm OK. Wasn't too hard, just took about 6 hours of my time. No more rattly startup, no more knocking noise while driving down the freeway.

The bearings I pulled out had physical pits in them - not sure how that happens. If anyone knows how that happens, I'd be curious to hear. Grooves, lines, and copper I can understand... but pits? I dunno.

So, hopefully I extended the life of this lil motor a while. It runs great. If your motor is lightly knocking, you might consider doing this. Pretty easy, and inexpensive.

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85 GT 2.8/Auto (daily driver)
2 x 86SE 2.8/Auto (parts cars)
79Z28 / 94Z28 / 98Z28 / 93 Suburban
1 wife who thinks I'm nuts...

metallurgical imperfections in the steel is the right answer.

Your lucky you caught it in time. Long term knocking can pound the rod cap out of round and a new bearing wont help due to the egg shape that occured.
Plastigauge would of found this during reassembly. Also make sure you have a good oil filter that does'nt drain down when you turn off the engine. Check the archives.....

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Pits? Old acidic oil sitting in an engine thats benn sitting a long time?

Had a similar experience with the used 3.4 I put in my car. It had a real faint knock noise that I traced to the #2 rod. I swapped out the bearing on that cylinder and it looked fine other than what appeared to be pit marks. The engine has been running strong with no knock for about almsot 2 yrs and over 15,000 miles now.
My bearign did not look as bad as yours but hopefully you will have the same luck I did.
Rich

I think the pits are caused by the type of oil that was used in it. Acid and so forth. You just cannot beat Mobil 1
Don

I'm probally endin up getting a diffrent engine but my Duke "makes engine noise" I duno what it is cause i havent heard it but I was hoping to just do what you're doing, or something up top. Just something simple to fix it. Glad to see that this did fix yours

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Good Job!

saved yerself much $$$

I had a bearing go bad on me too - it was worn, but did not spin. it did mess up the crank a little, but I was able to polish it out with 800 grit sandpaper. I dropped the oil pan a year later, to check up on it - good as new.

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1985 Fiero SE - Plain Red V6 Coupe
3.1 Crane272 MSD 4.10-4spd DarthChip Borla
D.A.M.M. - Drunks Against Mad Mothers

Thanks guys. Yeah, I have no idea on the history of this motor, so I don't known how many miles it has, nor how much time it has spent "sitting". The previous owner used Mobil1 Oil and filters, so I don't think it was his doing. But it is doing just fine - gave me 35 psi in park this morning after 20 minutes of running.

I typically use AC Delco filters and Valvoline motor oil. I won't put expensive oil & filters in it (c'mon, it's a bone stock Fiero I use for daily driving ), but I don't do the dirt cheap stuff either. Since I have too many cars (LOL), I buy cases of Valvoline at a time, and use it in all of 'em (except the race car).

And Pyrthian, your posts (found while searching) were one of the reasons I just went ahead and tried it. I figured I'd roll the dice and see if it worked.