what could cause this main bearing failure?
what could cause this main bearing failure? 
started losing oil pressure, crank was recently cut .010" and machine shop said everything checked out ok. main bearing clearances were .0025" during assembly. put maybe 500 miles on it.
any ideas??
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1st thing is who checked the crank after the machine work? Is it straight? From the looks of it I suspect the crank in not straight. Also did you install the crank? Did it spin free? Are filets on the journal properly dressed? From the pictures I don't see proper filet on the edges of the journals.
i also suspected that the crank is not straight, however the machine shop spun it in a lathe and verified it was straight according to them. I did install the crank and verified it spun over by hand with little to no resistance which lead me to believe i should have no issues. As far as i can tell i compared the filets to another factory crank i have and they look to be the same profile and depth.
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I would say 1st thing is have the crank checked before assuming anything else. If the clearances were right and align bore reasonably straight what else could it be? The journal in the pictures sure looks wrong to me.
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I'm assuming the rod bearing all look ok? Doesn't look like oil starvation. I would have the cranked checked by someone other than who cut it. I'm going to guess the journals are cut off center. Good Luck
Last edited by RockinWs6; Nov 26, 2016 at 10:26 AM.
Main Cap Direction ? My observation states #2 & #4 are the most damaged.
NO "mains" are ALL .0025", some kind of story ?
I see no "good" marks from the bearing tangs on the complement shells.
I may see, from the pictures, that #1 and #5 are marked.
My memory is that LS mains "kiss" the Tangs.
Did you mark the main direction, not the order ?
I also observe very HOT oil temperature.
Lance
NO "mains" are ALL .0025", some kind of story ?
I see no "good" marks from the bearing tangs on the complement shells.
I may see, from the pictures, that #1 and #5 are marked.
My memory is that LS mains "kiss" the Tangs.
Did you mark the main direction, not the order ?
I also observe very HOT oil temperature.
Lance
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Notice how 2 and 4 shrank? That's usually caused by heat.
I would suspects possible assembly error.
How does the rest of the crank look?
How do the bearings in the block look?
What do the rod bearings look like?
I would suspects possible assembly error.
How does the rest of the crank look?
How do the bearings in the block look?
What do the rod bearings look like?
pay no attention to how i have the main caps oriented on the bench as that is not how they were removed. All of the mains are numbered 1-5 and also have an arrow facing forward so i know they were all assembled correctly. I know 1-4 have the little feet facing backwards and 5 is flipped to allow clearance for the rear main cover. As far as the other bearings go, the cam bearing have no copper showing and just light scoring due to debris. The rod bearings are the same with no copper and scoring due to debris. I can post pics of these later. I did mic all of the journals today and verified they all measure the same in multiple locations. However what i did find was that i layed the crank in the block with only 1 and 5 main bearing installed. With a dial indicator i checked runout on all the mains. 1,4, and 5 showed .0005" or less. 2 and 3 showed .003" of runout. Im not sure how, but somehow it seems as though the those journals were cut off center. I installed a factory crank i had sitting around with the appropriate bearings in 1 and 5 and found it had 0 runout on all the main journals.
Im going to have another machine shop verify my findings just to make sure but i believe it was an error when the crank was cut. I just find it hard to believe my previous machine shop could not find this runout that i just found.
Im going to have another machine shop verify my findings just to make sure but i believe it was an error when the crank was cut. I just find it hard to believe my previous machine shop could not find this runout that i just found.
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Sorry to say this but as soon as I seen the crank wear I knew it was the crank cut off center. Being able to spin the crank while assembling is a good thing but once the crank gets a few tons of pressure on it the machine work quality comes out. Don't waste your time with who ever did this, move on and buy a good crank from a quality seller. Good Luck
"I just find it hard to believe my previous machine shop could not find this runout that i just found."
Likely, they ground it, knocked the fuzz off, and called it good. Shitty workmanship is easy to "find"...
As mentioned: A new crank, from a shop that knows WTF is going on.
Likely, they ground it, knocked the fuzz off, and called it good. Shitty workmanship is easy to "find"...
As mentioned: A new crank, from a shop that knows WTF is going on.
Main Cap Direction ? OK, I do NOT believe I have EVER had the ABILITY to "spin" a set, torqued, installed into the block crankshaft with a .003 run out.
NOW this could be possible with a VERY LARGE bearing/journal clearance.
I ask for the Bearing Manufacturer, Part #, and Journal Size ?
Lance
NOW this could be possible with a VERY LARGE bearing/journal clearance.
I ask for the Bearing Manufacturer, Part #, and Journal Size ?
Lance
Main Cap Direction ? OK, thanks.
I will take the time to measure, again, what I have on hand.
My observation states that the "thrust" has the witness marks of incorrect direction.
The pictures you gave might just be miss-giving.
Could you picture the Block Thrust center area ?
Lance
I will take the time to measure, again, what I have on hand.
My observation states that the "thrust" has the witness marks of incorrect direction.
The pictures you gave might just be miss-giving.
Could you picture the Block Thrust center area ?
Lance
After a crank chewed up the bearings you can't assume it's not straight due to poor machining. You put heat into the 2 and 4 bearings and it also shows transfer on the crank. I would expect it not to be straight after that.
Really need to see the block side of things too.
Really need to see the block side of things too.
well i dropped my block and crank off at a different machine shop wednesday. First look at it he agrees that its very possible the crank was not cut correctly. I will update the thread after i hear some results back from the machine shop.
On The Tree
Joined: Jul 2010
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1st thing is who checked the crank after the machine work? Is it straight? From the looks of it I suspect the crank in not straight. Also did you install the crank? Did it spin free? Are filets on the journal properly dressed? From the pictures I don't see proper filet on the edges of the journals.
I used to grind crankshafts and can say it's very difficult to cut the mains off center. Once the crank is centered in the machine and zeroed all 5 mains are cut in succession, usually with a steady rest on the #3 main. These are usually cut after the rods to avoid any relieving of the metal when the rods are cut to ensure a straight shaft.
However, the best cut crank in the world is useless in a block that doesn't have straight mains, which is what this looks like to me.