What killed these SBC rod bearings?

[RonRonnster]

Years ago I owned a 1996 Suburban with the Vortec 350. I bought it for $500 knowing it had a bad transmission, and knowing it had a questionable maintenance history. The previous owner did overheat the engine, and had fresh heads installed when I purchased it. I replaced the tranny in it at 145,000 miles and drove it another 15,000 before a rod knock in the engine surfaced. I put a new (salvage yard) engine in it and drove for another 30,000 miles before selling it - nearly 10 years ago now. Anyway, I've been going through a bunch of old stuff and found that I had kept the knocking rod bearing I found when I pulled the engine and tore into it. It was the only spun bearing I found, the rest were nice and tight (although maybe they were about to let go too at any time).

Based on the photos below, is there any way to tell what type of failure occurred with this bearing? I'm wondering if the engine overheating damaged it and it ground itself down over the course of 15,000 or so miles. It was never run low on oil when I had it - although it did have pretty low oil pressure when warmed up, if the dash gauge was to be trusted.

 

[Chris142]

http://mechanicalinventions.blogspot.com/2014/12/connecting-rod-bearing-failure-analysis.html?m=1

 

[Rand]

which bearing was it?

 

[spasm3]

I think it was overheated. The bearings wiped the crank with too little oil film,and the bearings continued to be chewed up over time. The crank will need to be polished or even reground undersize to get a smooth surface. The low oil pressure when warm was a tale tale sign that the main bearing/s were loose.

You will probably need to resize the rod ends as well.

How do the crankshaft main journals look?

 

[Rand]

Originally Posted by spasm3

You will probably need to resize the rod ends as well.

How do the crankshaft main journals look?


He wont need to do any of that.. this was off an old vehicle he got rid of years ago.

 

[spasm3]

Originally Posted by Rand

He wont need to do any of that.. this was off an old vehicle he got rid of years ago.




Gotcha

 

[Propflux01]

It didn't look like it got real hot, as the bearing is not discoloured. Probably a lack of oil at one point, long enough to start the wear process, and it just took some more mileage to finally kill it off.

 

[Linctex]

Originally Posted by Rand
which bearing was it?


I'm guessing it's the farthest one away from the oil pump

 

[clinebarger]

That bearing didn't spin, The locating tabs are intact.....I've seen inserts stacked on top of each other!

Like Linctex.....I'm guessing this is the #1 rod bearing?

 

[rubberchicken]

Was the oil filter mounted horizontally ? My 97 Suburban 454 4x4 is like that, and I found that the filters I was using did not have ADBV, so I would get a somewhat noisy startup. I switched to better filters and the problem went away. Later I installed a dual-filter bypass system. It now has 105k miles on it and the engine runs like a champ. The body is a bit rusty though.

 

[RonRonnster]

This was rod bearing number 2 - so it was definitely toward the front of the engine. It's likely #1 was about to let go real soon. Lot's of metal flake in the oil right before I pulled it. I wish I could find the pictures I took of the engine after I took it apart and eventually sold the core to a machine shop. Don't remember what kind of shape the crank was in. Wish I had better documented the parts as I took them off, but was in a hurry to get the new engine in so I skipped writing anything down. I was able to swap the new (to me) Vortec 350 into the Suburban in a couple days with the help of a good friend.

This is one out of two engine failures I've had in my life, likely due to poor maintenance by previous owner. The other engine failure was a 2002 Nissan Altima with the V6 engine. The timing chain tensioner guide broke off while on the freeway at going 70 MPH, skipped several teeth, and took out a few valves as it came to a stop on the side of the freeway. I purchased that car used, with over 220,000 miles on it. Hard to say if that was caused by previous neglect or just 220,000+ miles of use. Sold it to someone who picked it up right on the interstate and put another engine in it - still see it driving around once in a while.

 

[bbhero]

Possibly bad maintenance from previous owner... Though some VQ motors had issues with timing chain issues too. My VQ motor has 262k miles and runs great still.

 

[RonRonnster]

Originally Posted by clinebarger
That bearing didn't spin, The locating tabs are intact.....I've seen inserts stacked on top of each other!

Like Linctex.....I'm guessing this is the #1 rod bearing?


Good point - sure enough the locating tabs are still intact. I looked at the back of the bearing and assumed it must have spun, but now that I think about it, it doesn't look too bad on the backside.

I find the wear pattern interesting on the ends of the bearing, where the two halves meet together. The color is not shiny, like the rest, and the surface texture is different too. More of a rough texture instead of smooth grooves like the rest of it. You can see this up close in photo #3.

 

[aquariuscsm]

Any idea what oil the po was using (or wasn't using )?

 

[supton]

Evil cold start wear is my guess.

Dunno. Looks like grit in the oil.

Wild guess: any chance this might have been one of the motors where the owner decides to drain oil and then crank for a second or two to "get all the bad oil out"? I'm wondering if this was low speed no oil damage.

 

[DoubleWasp]

Previous owner previous incompetence can be a silent and slow killer. Here's LS bearings from a 14k mile engine. No, not 14k with the new owner. 14k total.

I've kept these, because this is the universally worst set of bearings I have ever seen come out of a running street car.

 

[khittner]

Must've had 56K 1/4 miles.

 

[DoubleWasp]

I wouldn't bet against that theory.

 

[WyrTwister]

I know next to nothing about such things , but was the oil pump defective ? Oil filter flowing poorly ? Oil pick up strainer clogged ? Not attached properly to the pump and sucking air ?

The inevitable low on oil question ?

 

[RonRonnster]

DoubleWasp - I would never have looked at those and guessed they came out of a 14k mile LS engine! I guess mine hadn't worn down to the copper yet.

Like has been suggested by members in this post, I suspect abuse or neglect by the PO caused this problem for me. I knew the PO, and knew going into it that he was sketchy on his maintenance. I also later found out that when the heads had been replaced, it was done by a shade tree mechanic in his backyard. Nothing wrong with that (I replaced said engine in this Burb in my driveway) but you never really know if crud got into the engine at that point or how careful the shade tree was when doing the head work.