Crankshaft Question

DieselDemon18

Member
Aug 25, 2011
48
7
8
Moreno Valley, Ca
Howdy folks

Now before i begin im just going to let it be known i used the search bar before posting this and the results are inconclusive.

Now back to the task at hand. Myself and a buddy are starting to build a motor him and lbz and myself an lb7. Now going back and forth and him doing research has me wondering about using stock cranks.

Our combinations will be similar as will our power numbers, both will be running socal rods and mahle race cast pistons both 16.8 CR, stock fuel, he will be running a 3794VA, and im running a 4094R, now we are both relatively on a budget (which is a oxymoron i know) he wants to do a callies which i would like to also but time is a factor and so is money in a sense, now i was going to reuse my stock LB7 crank and he has a known good, magged and check keyed lb7 crank he was going to use.

Our power levels will be the same about 600 hp give or take daily with it being 800 hp capable but the biggest thing for us is we tow our rv's with them plus have fun at the drag races, freeway pulls etc.. in a nutshell we want to be able to have fun and be able to thrash on it while not having to worry about reliability too much, so what are yalls thoughts/opinions/experiences on the matter? Im sure some of it is a case by case basis but im thinking ill be good with my lb7 crank, im just looking for any input.

Thanks
 

bimmer95

Member
Mar 15, 2019
58
5
8
Morgantown Pennsylvania
I'm no expert in the science of duramax cranks,but it's surprising how many used cranks break within 20k after a rebuild.I quit using them on the rebuilds I do,either new oem or callies.I know 'checking' a crankshaft at a machine shop doesn't mean much..but who am I to talk my personal truck has the original 300k crank and two rebuilds on it.

Sent from my SM-G981U using Tapatalk
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
18,206
440
83
Phoenix Az
If your worried about it, step up and buy a Callie’s or a narrow rod journal crank so you quit worrying. It will always be in the back of your mind otherwise. Hated that thought when I was on a stock crank
 

OleBlackyLBZ

Active member
May 22, 2020
213
40
28
I broke a used lbz crank in 28,000 miles. The only way I would EVER run a stock crank again is if it was brand new. And at that point your just $400 away from a new callies. I went new callies this time...
 

Bdsankey

Vendor
Vendor/Sponsor
Feb 1, 2018
2,647
177
63
Neenah, Wisconsin
I personally have used 2x stock LB7/LLY cranks on my personal engines. One has seen 1300hp and the other will be in my compound turbo tow rig. With that said, I would preferably run a new crank and be done, be it a NOS GM LB7/LLY crank or a Durastar as that thought will always be in your mind like James said of "is today my day?".
 
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LbzJason

2007 classic lbz
Jul 5, 2015
10
1
3
Lake Elsinore
hey Guys, so iam the one building the Lbz motor, I was getting a lot of mixed reviews about the crank so id say safe bet would be just buy the callies crank. What are your guys thought on doing the AF Cam with it? just getting into my first build and would like to not have 2nd thoughts about it when its done.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
18,206
440
83
Phoenix Az
If your not going to run a narrow rod journal crank, put an AF cam in it. Might as well put as many bandaids on as you can to give it the best chance.
 

LbzJason

2007 classic lbz
Jul 5, 2015
10
1
3
Lake Elsinore
I don't think the AF cam is worth the money. The new crank for sure is...
yeah definitely going to be buying the crank, and from what I was able to find was the AF cam changes the firing order and takes the hit off the front of the crankshaft where they are weak correct?
 

NevadaLLY

Adam B
Feb 24, 2019
305
27
28
Reno, NV
I am running the stock LLY crank in my build and using an AF Socal 3388 cam. My crank was mag checked and it looked good. Stock bearings looked brand new, no burns or burs. The crank mic'd out perfectly in spec so it was polished an setup for the new build. With a little bit of weight added to the crank for the heavier rod's/pistons it all seemed to add up just right. It's now balanced within 1g. Factory balance can really be an issue with some being as much as 15g (i've heard) out of balance. LBZ and up seemed to be more suspect for breaking due to heavier weight to offset the rotating assembly. On mine, I also added a super damper and it seems to run very smooth. I hope I'm not the guy with a blown crank in 20K miles but I was willing to put it to the test.
 

OleBlackyLBZ

Active member
May 22, 2020
213
40
28
I feel proper balancing has a huge impact on crank life. My first re-build that lasted 28K was balanced with a stock flexplate and balancer that they had there at the machine shop, then I was told I could just re-use mine. This time around I am using All-Season and they sent me the exact flexplate and balancer that was used to balance the rotating assembly. Then I am sending mine back with the core, I'm no engine builder but I like the way it's being done this time around. (y)
 
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Animals1234

Member
Jun 8, 2017
43
3
8
I currently have a motor with a Callie's crank and SoCal 3388 cam in it and have been very pleased with it. In the back of my mind though I know it's not a permanent fix to Duramax crank problems but it will definitely prolong the life of my motor.
 
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Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
18,206
440
83
Phoenix Az
yeah definitely going to be buying the crank, and from what I was able to find was the AF cam changes the firing order and takes the hit off the front of the crankshaft where they are weak correct?
It stops some of it but does not stop them from breaking. Only fix is to actually address the problem area at the rod journals
 
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DieselDemon18

Member
Aug 25, 2011
48
7
8
Moreno Valley, Ca
It stops some of it but does not stop them from breaking. Only fix is to actually address the problem area at the rod journals
That makes sense but i wont be running massive power, maybe 650 at the most, but i will be towing heavy at times (on a lesser power tune) i think a callies or even a lb7 crank will live at that power level, what do you think?
 

NevadaLLY

Adam B
Feb 24, 2019
305
27
28
Reno, NV
That makes sense but i wont be running massive power, maybe 650 at the most, but i will be towing heavy at times (on a lesser power tune) i think a callies or even a lb7 crank will live at that power level, what do you think?
It’s not really about power level. Stock cranks can break at stock power. It’s all harmonics. Adjusting the firing order helps move the harmonic profile, but it’s not a sure fire answer. As others said, the only guarantee is to address that specifically. I chose to make an educated guess based on the crank I had and what my risk level was. That’s what you’d be doing with an LB7.
 
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DieselDemon18

Member
Aug 25, 2011
48
7
8
Moreno Valley, Ca
It’s not really about power level. Stock cranks can break at stock power. It’s all harmonics. Adjusting the firing order helps move the harmonic profile, but it’s not a sure fire answer. As others said, the only guarantee is to address that specifically. I chose to make an educated guess based on the crank I had and what my risk level was. That’s what you’d be doing with an LB7.
It makes sense, ill proably be going with a callies if socal has one in stock but now the next question is balancers. Already have a new balancer and flywheel for an lb7 on the shelf for a the build, wondering if i have to switch that up as well
 
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LbzJason

2007 classic lbz
Jul 5, 2015
10
1
3
Lake Elsinore
It makes sense, ill proably be going with a callies if socal has one in stock but now the next question is balancers. Already have a new balancer and flywheel for an lb7 on the shelf for a the build, wondering if i have to switch that up as well
Let me know what you find out about the balancer and flywheel, looks like we are going to be buying some cranks haha.
 

NevadaLLY

Adam B
Feb 24, 2019
305
27
28
Reno, NV
Let me know what you find out about the balancer and flywheel, looks like we are going to be buying some cranks haha.
I went with super damper (better for the higher HP application) and also upgraded the flex plate to a BD. Neither are required but I found cracking in the OEM flexplate.
 

DieselDemon18

Member
Aug 25, 2011
48
7
8
Moreno Valley, Ca
I went with super damper (better for the higher HP application) and also upgraded the flex plate to a BD. Neither are required but I found cracking in the OEM flexplate.
Thats what i have is a bd flex plate along with the lb7 fly wheel for the same reason, i found cracking on mine, looks like ill have to squeeze out more money for a damper haha, damn thisnhobby is expensive but it sure is fun
 
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