LML Crank Nightmares

[RobsDmax]

Hey guys,

I have been daily driving a 11 LML that I bought from original owner with over 600,000 miles on it, I am at 705,000 miles now. At 675 or so it needed head gaskets, so I did ARP studs, grade Cs, hsp piping kit couple other small upgrades and CP3 swapped (had original CP4 in it ). Anywho fast forward a bit and it hits 704,500 and breaks the crank at the back. I’m not complaining it lasted 700+ and I’d just added a pile more cylinder pressure too it etc. So found a “good used” 150,000 mile motor to swap. Ended up that one had one bad piston (cracked) so we swapped in one of the others and put it in. It went about 500 miles on this motor and this cranks now also broken……..

I’m looking for a couple answers and I know I’ll get them here.
1 - Can I use a LB7 short block (I have a couple and they aren’t drug money like a LML) and swap the LML heads etc onto it.

2 - Is it just poor luck that the spare motor broke the crank also? Or is there anything specific truck side that anyone can think of that would cause the issues with cranks…

Thanks as always,

Rob

 

[TheBac]

What were the "other small upgrades" that added cylinder pressure to the first engine, Rob? Did you carry over those same mods to the new engine?
Also, the cracked piston in the new engine leads me to believe that one had issues before you installed it, so it may have been living on borrowed time in the first place.

 

[RobsDmax]

What were the "other small upgrades" that added cylinder pressure to the first engine, Rob? Did you carry over those same mods to the new engine?
Also, the cracked piston in the new engine leads me to believe that one had issues before you installed it, so it may have been living on borrowed time in the first place.

Biggest things were the new head gaskets and studs since it needed head gaskets, the HSP air bundle, downpipe, and a drop in Midwest/CRT charger. Everything went onto the “new” engine except the charger it was far too loud for me.

I’d have to agree I’m just curious on opinions far smarter than mine! Hoping I can use one of the LB7s I have here but I’ve heard multiple yes and no’s!

 

[Chevy1925]

stock power level still though?

you will run into getting the water pump hose to fit correctly, might be a simple fix or might not be. the reluctor wheels need to be changed on the crank and cam to match the lml which to make it simple, the cam gear needs to be changed to LML. the mid plate will need to be changed or left alone depending on how you have the egr cooler setup. there might be some other small differences but shouldnt be major. the LML heads should bolt right to the LB7 block and as should the accessories.

if it were me, id put the LML oil pump, pan, front cover and all that jazz on the LB7. you get a better oil pump and more flow from it.

 

[RobsDmax]

stock power level still though?

you will run into getting the water pump hose to fit correctly, might be a simple fix or might not be. the reluctor wheels need to be changed on the crank and cam to match the lml which to make it simple, the cam gear needs to be changed to LML. the mid plate will need to be changed or left alone depending on how you have the egr cooler setup. there might be some other small differences but shouldnt be major. the LML heads should bolt right to the LB7 block and as should the accessories.

if it were me, id put the LML oil pump, pan, front cover and all that jazz on the LB7. you get a better oil pump and more flow from it.

Yessir just tuned and deleted single tow tune in it. The big thing I’ve heard is the engine mounts are different?

 

[Chevy1925]

Yessir just tuned and deleted single tow tune in it. The big thing I’ve heard is the engine mounts are different?

yeah, just did a quick search and the pass side mount seems to be a big issue...

LBZ long block to replace my LML

I have a mild built LBZ long block bought it to replace my tired motor in my 2006 single cab but i just finished puting a compound kit in my 2016 gmc anyone know be sides swaping heads injection parts what else or should i say LBZ short block in 2016

www.duramaxdiesels.com