what would have caused this main bearing failure

Jul 27, 2007
motor only has 50 miles in it and chewed up number 3 main. oil clearances were .0017-.002 oil pressure was around 20 psi hot idle and went up to 60psi around 2500rpm . i checked the crank to make sure the journals weren't out of round any ideas IMG_0865.JPGIMG_0866.JPGIMG_0861.JPG
Dry start?? Did you prelube the system?
Crank been reground?
Block line honed?
Rod brgs look like?
W/the rise of the oil pressure, could something have blocked the oil passage causing a loss of oil to the bearings?
i primed it before start up and crank was cut 10 10 and line honed i checked it with a straight edge and its good. the rod bearings look like new. the block i cleaned twice and used them long brushes to clean all the oil ports
So you had the crank turned and the main line was align honed and you assembled the short block?

This is not an oil starvation issue, either the crank or main line clearances were not properly set, and a straight edge is not a method to check for clearance or alignment.

My guess is that journal was too tight at the start up, and you should first have the block checked with a bore gauge, and the crank with a micrometer so you know what tolerances you have, as they obviously are not correct. :confused:
In defense of the guy asking for help, checking the main saddles in the block with a straight edge or precision round bar is a good preliminary check to see that the main bores are all on the same axis. But this is not a substitute for proper measuring of the main bore.

Regalracer 1987: You need to beg, borrow or buy a precision bore gauge and a 2-3 mike. (Both need to read to .0001") Measure each main bore with the bearings removed, caps in place and torqued to spec. Measure in several different places around each bore for out of round. Measure each bore front to back and look for taper. The spec on the main bore is 2.6870"-2.6880" You should be right in the middle of these specs with only .0001 or so out of round or taper. When I line hone one of these blocks I always shoot for the minimum spec. so I can keep bearing crush at the maximum.

Drop your crank into the block with only #1 and #4 bearing upper shells in place. Leave the caps off. Mount a dial indicator on #2 or 3 main journal and measure the crank for T.I.R. (total indicated runnout) this should be .001 or less on a good straight crank. Something is off and you need to play detective to find out where the problem is hiding!!

Chances are your main bore or your crank is not right.
i had the block line honed because i put in arp studs in and yes i always put a straight edge across the main saddles and check for clearance with a feelers gauge just to do a quick check to see if its straight. when i put it together i did mic the crank and used a bore gauge. but didnt cross my mind to check the run out since i was rushing even tho i shouldn't have to get it together for bowling green im gonna check the run out tonight im pretty sure something is gotta be out of round or maybe human error with the bore gauge
I certainly don't have 1/100th the experience you guys have but I haven't yet had success running clearences that tight( .0017-.0020) on these turbo buicks. I do have success using .0023-.0025. And I will no longer use Clevite P series again.

Let the flaming begin!

I like to set the the clearances tight for a street engine. .0015-.0018 on rods and .0020-.0022 on mains seems to work well for me. The crankshaft journals need to be darn near perfect to run tight clearances. Journal defects like out of round or taper will kill the bearing.

I have had great luck with Clevite P series bearings. Unfortunately Clevite stopped making .001 P main bearings, so selective fitting is out of the question. I switched to FM mains.
One thing I would look at is the main web casting marks on #3 from the saddle to the cam bearing bores. A crack here could cause a tight bearing after it has run a while even though it has been line honed, and it is very hard to see it if it is just starting. Magnafluxing the block would show it. If the crank will not turn by hand with the caps torqued, you have a problem. That's assuming the crank mikes out OK and is straight, and the clearances are correct. The bearings in the photo look like they were pretty tight. Just something to consider while it is apart. You may have had the block checked on the first build, but if not, you may want to do it now.
Its a good idea (if possible) to use the same torque wrench to final torque the mains as was used to torque the mains for line honing
i had that same thing happen to me it turned out that my new 2 center caps were installed to tight and it was line honed !!
Not sure if the "old school" tech still applies to line honing...When Ruggles did mine, he had the Sunnen rep show him how to use the hone.
It had to do with the block being so short, and the hone wobbling. He described the problem as tite on the center bores, loose on the ends...
It would be interesting to see what the dial bore gauge says about these bores.

I was trained by our regional Sunnen rep on the CH-100 Line Hone. He told me that very few machine shops can properly hone a shorter block like the Buick V6. He explained that you must remove a couple pairs of shoes and stones from the mandrel. It effectively shortens the mandrel. But you need an entire set of stones and shoes just for honing shorter blocks. Most shops are not willing to buy an expensive set of stones and shoes for just a few blocks. They try to make due with the longer mandrel and end up loosening caps to control oversizing the end bores.