Stress cracks on connecting rod bolt holes?

[rb68rr]

While installing rod bearings the shop noticed small cracks on the edge of the bolt holes on a few of the connecting rods. On one in particular the notch on the bearing has a gap at the edge of this bolt hole where the rest are flush. Anybody else seen these cracks and is it a big problem? Should I replace the rods? What causes this? Do the heads now have to come off? DAMN!!! Thanks, R.B.

 

[blackbuick87]

Why was it in the shop in the first place. A little background might help.

 

[timstips]

Bad rod bearings.

 

[machinegun]

It sounds like detonation has been prevelant at some point. I would have rods magged to make sure but you will probably need new rods or at least I would replace them. Why take chance.

 

[timstips]

What causes these cracks? Will the new bearings be ok with these small cracks if I don't replace the connecting rods? Right now money is a BIG problem.

 

[blackbuick87]

Originally posted by timstips
Bad rod bearings.

Until you determine why the rod bearings went bad in the first place you are just spinning your wheels.

Dentonation would be the most common cause, so you need to figure out why the engine is setting off the knock sensor. Either too much timing, too much boost, bad tune, cracked headers, blah blah.

What I am saying is if you throw it back together and do not find out what is wrong, IT WILL fail again

 

[timstips]

Right now I just need to get the motor back together. Will these cracks cause the new bearings to fail?

 

[BoostKillsStres]

If any of those rods with the cracks fail you could loose the rod, crank and possibly a block depending on when it decides to let go. I'm not sure exactly where your seeing these cracks but if I saw a crack ANYWHERE on a rod, bolt area or otherwise I'd consider them junk...sorry.

 

[timstips]

Thanks, anybody want to buy a fu##%%g car?

 

[blackbuick87]

Originally posted by timstips
Thanks, anybody want to buy a fu##%%g car?

Where are you located?

 

[timstips]

Crandall, Texas

 

[PaulRV6]

Timstips, don't panic. I went round and round on this exact same issue. With many folks on this board and my engine machinist.
Does not appear to be a problem. 5 out of 6 of my rods were like that but it was determined that they were like that from the beginning.
I would not get new rods because they may be the same way. The rods are very thin in that area and when the notch is milled out they tend to break out.
I will look for the thread I started on this and send it to you.

paul

 

[PaulRV6]

timstips, here is the link (you may have to cut & paste).

http://www.turbobuick.com/forums/showthread.php?s=&threadid=46625

paul

 

[rb68rr]

Paul, thanks for the information. Did you go ahead and use the ones with the cracks? If you did have you had any problems? Any more info about this would be greatly appreciated. Thanks, R.B.

 

[rb68rr]

HEY UNGN!!!!!!

Hey Chris, I really respect your opinions on questions on this board. Would you please give me your assessment of the small cracks on the connecting rod bolt holes? Will they be ok to use again if necessary? BTW, this cracks are very small, maybe 1/16th of an inch. Thanks, R.B.

 

[rb68rr]

ttt

 

[rb68rr]

ttt

 

[turbocamino]

I'm in the process of rebuilding a 87 GN motor to put in my 86 El Camino. A guy that I work with had nothing to do one day, so I had him polish the beams on the rods. Not that this needs to be done in a relitively low RPM motor like a turbo motor, but we did discover two hairline cracks (more likely casting flaws) in the sides of the beams where the bolt comes thru. The bearings were in good shape when I took the motor apart, and the car had very few performance mods. I would imagine these cracks, (or flaws) were there from day one. I didnt like the idea of having a defect in the rods, so I got two other rods from the junkyard that were good. If I was in your shoes, and my description sounds like your rods, I would probably just put the motor back together. This is just my experiance and my opinion, so do what you think is best. It's your motor!!!!!!!! Good Luck, Jeff

 

[PaulRV6]

Yes, I am using the ones with the cracks (not the best choice of words) as recommended by the machinist. Since an earlier 4.1L motor I disassembled had the same type of flaws.
I am still convinced the rods were like that from day one.

paul