LBZ crank in LB7?


New member
Jul 28, 2022
Firstly, I've searched and dug through threads and can't get a clear answer on this. Your knowledge is greatly appreciated.
I bought a non-running truck, and after messing around a while noticed the harmonic balancer moved like a cam while cranking.
I tore the bottom end apart, and the mains are spun and the crank is roasted pretty bad. I think the block is ok and I'm taking it to get checked out soon.
Got a used LBZ crank, and my question is if it needs to be balanced with all the old pistons and rods, or if it's fine to run with the LB7 harmonic balancer and flex plate. I'm not planning on keeping the truck, it's got just over 100k on it so I want to fix it right and sell it again.
I'm not planning to replace anything except rod and main bearings, unless, of course, the block is shot.
The oil pick-up tube is broke completely in two and bent as well. No idea how it happened, but I'm guessing it contributes to the spun mains.


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don't know sh!t about IFS
Staff member
Oct 21, 2009
Phoenix Az
if you balance the LBZ crank to the rest of the LB7 rotating assembly, you shouldnt have any issues. if you want to just drop the LBZ crank in and run it without balancing, that might be an issue. based on old info, when GM switched to the LBZ, they didnt change teh weight at the fly weights of the crank, only at the flexplate and damper. So in theory, it should be a drop in for a stock rotating assembly but its theory as i never balanced the cranks back to back. It would be hard to know as rotating assemblys can be all over the place to balance correctly.

i will say, 99% of the time, if the mains spun in the block, the block is no good. until someone starts making oversized/undersized bearings for these engines, there isnt a way to save them
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Oughta Know Better
Apr 19, 2011
Western PA
The block can normally be saved, but a set of billet main caps is sometimes required as a last resort. Which may exceed the cost of another good used block.

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