Broken Crankshaft Count?

[GeorgiaDieselGTO]

Well I bought a truck with a broken crank, and after studying it all out, it is our inclination to think that it is caused by rpm more than anything. And i know that the guy that i bought it from would often take it up to 5000 rpms these motors are externally balanced which means that the weight of the balancer slinging around on the end of the crank is causing it to fatigue and eventually break. It is my thinking that an internally balanced crank in going to be the key to stop these failures.
Lets hear some more on this what is everyone elses thoughts? Oh and mine is an LBZ

 

[IdahoRob]

Well, we about beat the crank out of the block, but haven't broke one yet. Started out as a well used LB7, built and ran a full year at 900-1200HP and re-built it this month. Same crank is back in the engine for another season, we'll see.

 

[duramaxdiesel]

Wow Rob that's insane! Did you do anything to the crank? Cryo?

Nick

 

[GeorgiaDieselGTO]

Well, we about beat the crank out of the block, but haven't broke one yet. Started out as a well used LB7, built and ran a full year at 900-1200HP and re-built it this month. Same crank is back in the engine for another season, we'll see.

That is wats so crazy some take way more than others. what sort of rpm were you turning out of that one?

 

[mvnvltn]

Mine broke, I am checking now to see if it was balanced right or at all.

 

[duramaxdiesel]

Mine broke, I am checking now to see if it was balanced right or at all.

Built or stock motor?

 

[dmaxfireman]

bump for info.... did you ever get your stuff checked mvnvltn?

 

[TheBac]

I got a call from Ben tonight that his crank is probably broke.

 

[whitetrash21]

Ben?? as in Duratothemax.....???

What happened?

 

[03dmaxin]

i broke one to recently in my stock engine

 

[Rand1027]

Well I bought a truck with a broken crank, and after studying it all out, it is our inclination to think that it is caused by rpm more than anything. And i know that the guy that i bought it from would often take it up to 5000 rpms these motors are externally balanced which means that the weight of the balancer slinging around on the end of the crank is causing it to fatigue and eventually break. It is my thinking that an internally balanced crank in going to be the key to stop these failures.
Lets hear some more on this what is everyone elses thoughts? Oh and mine is an LBZ

So are you saying remove the balancer, and try just a balanaced crank?

 

[TheBac]

Ben?? as in Duratothemax.....???

What happened?

Just driving. Heard a "bang" and engine began missing and running rough. He looked underneath to see if any windows had appeared, and saw the balancer wobbling like everyone else has reported. He said he has to tear it down to make sure, but he's positive thats what it is.

He had towed 10,000lbs the day before. He thinks his engine's low oil pressure has a lot to do with this.

It sucks, but he was pretty upbeat in spite of it.

 

[MrUPS]

dang that sucks. Someone mentioned that some of these cranks take more than others and it got me to thinking. It seems that way with these motors in general. Some will take a never ending pile of abuse with out missing a beat (bullfrog's bottom end comes to mind) while others just fall apart under normal driving. Its really weird.

 

[05' Ditry Duramax]

What about running "seasoned" cranks. I know it seems to work with intermidiate shafts behind Cummins. Has anyone noticed the miles on the cranks? Have you guys used high mileage cranks that was in the enigine before the build? What about new low mile cranks? Maybe you can brake down (no pun intended) the use before?

Did it come out of a engine that was babied or one that was beat on really hard?

 

[Osubeaver]

What about running "seasoned" cranks. I know it seems to work with intermidiate shafts behind Cummins. Has anyone noticed the miles on the cranks? Have you guys used high mileage cranks that was in the enigine before the build? What about new low mile cranks? Maybe you can brake down (no pun intended) the use before?

Did it come out of a engine that was babied or one that was beat on really hard?

Not a metallugrical expert by any means, but the whole "seasoned" thing seems a little wierd to me. Anybody have any data to back this up one way or another?

Seems to me a crank undergoes stress from twisting and bending. The basics say if you twist and/or bend something enough times, no matter how little, it will fail eventually in theory.

I suppose there is the work hardening thing that could apply as well, although I don't know how much (or even if) in this application.

 

[duratothemax]

+1 for a broken LBZ crank. Whenever I get around to tearing it down ill post pics.

ben

 

[Cougar281]

+1 for a broken LBZ crank. Whenever I get around to tearing it down ill post pics.

ben

Man, that sucks.... Sorry to hear that. Hope you get back up soon!

 

[MACKIN]

+1 for a broken LBZ crank. Whenever I get around to tearing it down ill post pics.

ben

Well Ben,


Your mother told you to STOP your wrecking a good truck! :happy2:


Good luck,lil buddy

 

[duratothemax]

Well Ben,


Your mother told you to STOP your wrecking a good truck! :happy2:


Good luck,lil buddy

I just have to laugh, ironic that out of the 3 motors that have been in my truck, the one I ran the hardest with the littlest care to anything was my stock factory original engine...and everyone says LLY's are junk... : That made it 85-someodd thousand miles before cracking a piston. My "BUILT" motor lasted 15,000. This stock LBZ POS short block lasted about 50,000. Wonder how far Ill get on lucky #4. :joker:

ben

 

[LarryJewell]

I just have to laugh, ironic that out of the 3 motors that have been in my truck, the one I ran the hardest with the littlest care to anything was my stock factory original engine...and everyone says LLY's are junk... : That made it 85-someodd thousand miles before cracking a piston. My "BUILT" motor lasted 15,000. This stock LBZ POS short block lasted about 50,000. Wonder how far Ill get on lucky #4. :joker:

ben

my factory lly engine is still good (135,000 miles), hope I dodge all these bullets, sorry to hear about your bad luck Ben, hopefully # 4 is the last