Rod Bearing Failure Analysis

[Taylor]

Foreign debris & excessive crush, or oil starvation? Same story on all 8 cyl's, but the journals look fine. Bought from a guy w motor knock who bought at auction, and the title reveals it switched hands quite a few times in a short period, leading me to believe someone may have tried to replace the bearings, wasn't clean, and over torqued the caps, but all bearings have 98 on them, this is a 99' jeep, oil pan gasket was very stuck, none of the bolt heads were stripped, and rod cap bolts seemed to be consistently torqued. Going through the rest of the vehicle, doesn't seen like much was done in terms of maintenance. Oil pickup wasn't clogged or anything. Run low on oil, clogged passageway, incorrect installation, out of round crank? Thoughts?

 

[dparm]

Awesome Clevite website for diagnosing bearing failure:
http://catalog.mahleclevite.com/bearing/


PDF with more info:
http://www.wilmink.nl/Clevite/Clevite_lagerschade_tech_info.pdf

 

[Taylor]

Inside of rod cap;

 

[Taylor]

Backside of bearing;

 

[Pablo]

Dirt AND lack of oil = lack o' maintenance

perhaps

 

[Fleetmon]

It's hard for me to tell on this phone picture but it almost looks like the bearing "keys" were not aligned in the slots.....what does the back side look like? In this picture the shell still looks silvery so it appears to heve been oiled. The crushed tab (or key as I call them) looks similar to a bearing that spun but no evidence of extreme overheating by no lube....again, it's a very small picture I'm looking at.

 

[Taylor]

Yeah, I've looked at a lot of illustrations, etc, kind of a mix of a few, you can see wear near the parting, I was just hoping for some input from a builder.

 

[Fleetmon]

spun bearing....the new pictures show it clearly

 

[Pablo]

It spun alright but that's just a symptom, so to speak.

 

[Taylor]

Rod journal bore out of round? Go ahead and pull the motor to drop the crank, two-piece block, w 30 some bolts in the bedplate?

 

[Fleetmon]

The cap shows a tab mark opposite of where it should be? Wrong bearings?

 

[Taylor]

Originally Posted By: Fleetmon
spun bearing....the new pictures show it clearly


So the bearing was literally spinning inside of the rod journal? And thats indicated by the excessive wear, and discoloration of the backside? any sort of indications from the inside? all have a shinny spot near the 'key' on the inside.

 

[Fleetmon]

Yes....the wiped tab and scratches in the cap bore show a spin....it's odd that the crank side of the bearings aren't blue so it shows it had oil pressure or ran a very short while before failure. If all are alike (meaning evidence of a spin) and all are still showing silver on the crank side, I would look for 1) wrong bearings or 2) grossly oversized/undersized bearings. However, oversized bearings (meaning bearings purchased for a turned crank but the crank being standard) will typically show as overheated bearings.

 

[Taylor]

It may just be the pic, I'll get some better ones of each cap. The tabs are still raised on all bearings. They are all marked STD. Is it likely the mains or cams have failed as well? Thanks for the knowledge!

 

[Taylor]

Rod side journal bore;

 

[Taylor]

Rods need to be replaced? Next step to pull the crank and measure journals?

 

[Taylor]

Had good pressure;

View My Video

 

[GreeCguy]

Did the rod start knocking before you shut it down? What kind of RPM's were you running?

 

[Hokiefyd]

A '99 Jeep? Is this is a 4.7L V-8?

 

[punisher]

Is the tab/key just wiped out on the shell on that cylinder and not the others? Just curious how that bearing spun and didn't inflict anymore damage to the big end or the shell itself. Google the numbers from the bearing shells and see what it is. Does it match the other shells? I can't get over the lack of damage. Maybe it spun before and someone cleaned it up and threw in another bearing. Maybe the grooves on the back of the shell are just imprints from the rod/cap. Just throwing it out there. Any signs of discoloration/blueing on the rod/cap?