Crank replacement?

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Blackmax123

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Aug 2, 2014
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Just wondering if anybody has had any luck just replacing the broken crank with a new one without completely tearing down the whole engine and having the rotating assembly spin balanced?

My lml broke a crank shaft last Saturday night. Truck is all stock except for lift, tires and steering upgrades. 115k miles. Currently just a little short on cash and time. So I figured my best bet maybe to just pull the engine and replace it with a used complete engine. Or pull the engine slap in a new crank and put it back in.

I don't imagine the factory spin balanced every rotating assembly before putting the short block together. So I thought I'd probably be okay just to buy a new crank and run with it. At least long enough to make it till the machine shop can get my spare block ready, or to the dealer and trade it in a new l5p.
 
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Blackmax123

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Aug 2, 2014
683
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central Pennsylvania
I'll know this weekend how the block looks. But I have an lmm block in the garage that broke a crank and the block looks great.

Don't really see spending the money for an engine when it's getting traded in. Pretty much just wondering if anyone has just swapped cranks and had any luck.
 
Chevy1925

Chevy1925

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Oct 21, 2009
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you will need to tear the crank out and hope a bearing didnt spin in the journal or get hot and discolor the journal. if that checks out, i would then put a bore gauge in there and check for out-of-round and taper. if all that is good, i would feel better about throwing new bearings on the rods/mains and putting a new crank in.

the likely hood of this working out in your favor is slim but its possible. DO NOT PULL THE PISTONS/RODS if you want to make this simple.
 
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Blackmax123

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Aug 2, 2014
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central Pennsylvania
Kinda just trying to do this as quickly and simple as possible since the truck is most likely just heading straight back to the dealer I bought it from and getting traded in.

If I wasn't looking to trade it is just take the lmm block I have to the machine shop and get a new lb7 crank, use lbz rods and buy a set of mahle performance cast pistons. But I really don't need 2 trucks to dump money in. So main goal is getting it running and sending it down the road.
 
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S Phinney

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Aug 15, 2008
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Obviously the right way is a complete tear down but if the front main cap doesn't have any damage it would be fine to replace with another lml crank. Very seldom are there any damages. Any damage that I have seen comes from it breaking and still is driven until it just stops. At that point I usually won't use the block again. You could still salvage it but I prefer not to do that when the caps get damaged.


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Blackmax123

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Aug 2, 2014
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central Pennsylvania
I agree the right way to fix it would be to completely tear it down. But I'm not looking to build another engine. Just wanna part this together if possible to trade on a new l5p with a warranty.

I shut it off about 2/10 of a mile from when it happened. Towed it home on a flatbed. It will still start and run just has to crank a while.

So if the block is okay. It would be okay to just throw an lml crank in it.
 
Awenta

Awenta

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Sep 28, 2014
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I would get a used crank for cheap and some new bearings and slap it together. If it makes some funny sounds put some thick oil in it and trade it in.


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quinton

quinton

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Nov 28, 2011
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S Phinney said:
Obviously the right way is a complete tear down but if the front main cap doesn't have any damage it would be fine to replace with another lml crank. Very seldom are there any damages. Any damage that I have seen comes from it breaking and still is driven until it just stops. At that point I usually won't use the block again. You could still salvage it but I prefer not to do that when the caps get damaged.


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X2. Every one I have replaced I could just put bearings in and be good, I always take it to the machine shop though, if you didn't drive it long it should be fine. Pull it out and check bearings and caps
 
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Blackmax123

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Aug 2, 2014
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central Pennsylvania
I was gonna buy a complete engine but then decided to hold off till I check out the damage to mine. Then with the old lady being more than upset about me having to build another engine. She agreed if I could fix it cheap and make it to the dealer I was allowed to buy a new l5p as long as I leave it alone and just drive it like a normal person since I should've bought a new one when I picked up the lml. I've only put 11k miles on it since I bought it 16 months ago.

So in my thinking as long as the block is okay. A new lml crank and some new bearings should fix it enough to make it to trade or even as dependable as it was.

If I didn't spend as much money on my puller and this truck wasn't all stock and it was closer to the winter I'd have no problems just doing a budget build. But no sense in me sinking the money in a budget build and getting it back together to blow up a cp4 pump and be out about 5k
 
LBZ

LBZ

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Blackmax123 said:
When the engine oil was drained there's nothing at all on the plug and the oil looked like normal.
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Your probably fine then. Mine looked the same way when it broke behind main 4. Just a little bearing material in the pan. I drove it more than an 1/8th mile though lol. Pretty sure your block will be fine.

I'd go with the cheapest used crank you can find and new bearings if you are just going to trade it in.

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Blackmax123

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Aug 2, 2014
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central Pennsylvania
Haha.. I agree.. I hate used vehicles. I should've never bought this truck. But the price was okay. I know the dealer did some work to it before I got it. But I bought it with 104k on the clock. After changing tie rods, pitman idler arm and 16 months 11k mile later it sits with a broken crank. Something gives me the feeling it had a pretty rough life.
 
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Blackmax123

Member
Aug 2, 2014
683
1
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central Pennsylvania
Dozerboy said:
That what I was thinking, but who knows maybe it will go another 200k after the repair.


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This is my thinking also. If the block is good and I use a new crank and bearings. Probably gonna get the Empire pin kit and pin the damper. It will be as good if not better than gm sent it out if the factory.

If the block is no good it will get a budget built short block and I'll end up keeping it. I'm not the type of person to scab something together knowing it's not gonna last and let it up to the next person.

My whole question was just if anyone has had any luck swapping the same model crank with a new one without balancing the rotating assembly. I would feel 100x's better just tearing it all apart. Buying carillos, oval bowls, stud the mains and heads, a.f street cam and line bore, Magnaflux and hone the block. But also need this truck up and running asap so I can keep pulling this year. Other wise my puller sits till it's fixed.

Only reason to wanna trade it is to get into a new truck with a warranty so I don't have two money pits to deal with.
 
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