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The guy at the shop tells me that this is a semi-common problem with lbz engines. Anyone here ever hear that? Crank just snapped under zero load. Just heading down the road empty got about 80 k on it.
 

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yea its not entirely uncommon...

buddy of mine just washed out three main bearings and they told him his crank was near failure.
 

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omG! That doesn't sound right, do you have a magnified picture if the break to see the stress cracking and to determine if it was not a manufacturing defect. Where on the crank did it break
 

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yea its not entirely uncommon...

buddy of mine just washed out three main bearings and they told him his crank was near failure.
Seems like a crank should last longer, never had a crank failure in anything before. have not found cracks in aircraft engines doing magnetic particle inspection (not yet).
 

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They generally break at the #2 rod Journal.
 

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thats shitty, was the truck tuned?
 

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They generally break at the #2 rod Journal.
Now come to mention it, I think I have heard this before, but thought it was on tuned trucks, is this do some type of oil starvation at the #2 rod journal?
 

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Now come to mention it, I think I have heard this before, but thought it was on tuned trucks, is this do some type of oil starvation at the #2 rod journal?
No real way of telling, some think its from the motor being extenally balanced and running high RPMs..

Seen it on stock motors as well as highly modified. Just one of those weaknesses.
 

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you would think with the amount of torque these motors endure for hundreds of thousands of miles GM would have had the foresight to have isuzu internally balance the crank
 

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I know under grade braking my truck tries to blow it's self up at times. I hate when it does that...
Suicidal truck? Sounds like it needs help.

JK, what do you mean that it "tries to blow it's self up"?
 

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I've been told that gm balances their gas motor cranks to 25 grams. To spin 6+k rpm reliably in those it should e balanced to less than 1 gram. Also told the diesel cranks are way worse than the gasoline motors when it comes to being balanced...
 

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I've been told that gm balances their gas motor cranks to 25 grams. To spin 6+k rpm reliably in those it should e balanced to less than 1 gram. Also told the diesel cranks are way worse than the gasoline motors when it comes to being balanced...
You'd think aftermarket builds would be balanced to within 1 gram though, is this not an issue on balanced built motors.

Has anybody heard of the same issue on a balanced engine?
 

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Yea balanced ones have too. Must be metal defect in cranks. Big thread on this at duramaxdiesels.com

http://duramaxdiesels.com/forum/showthread.php?t=23186

Sent from my SPH-D700 using AutoGuide App
 

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did your truck kinda bounce in park at 14-1500 rpms before it broke? mines always done it you can tell somethings not balanced right but its got 178k hard miles on it.
 

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Not that i remeber. Just went bang while downshifting

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Did you build the motor once it broke of did you just replace the crank and keep on truckin? any other damage?
 

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Just bought ebay engine and took crank out of it to put in mine. Still running good today. No other damage. Checked piston petrusion and other tolerances

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Good to hear, How many miles ago was that and what was wrong with the engine that you didn't just swap the complete motor in?
 
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