Looking at the pic the crank looks like it had a crack in it for a while about half way through? Then you see what looks like fresh break?
LBZ: Broke my crank
- Thread starter BHoward6.6
- Start date
It does have what appears to be two different types of breaks. But I don't know if one happened long ago or both at the same time.
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From what I learned in materials class several years ago, it looks like brittle failure and ductile failure.
Ductile failure is where the metal pulls apart, brittle failure is a break with no stretch.
Ductile failure is where the metal pulls apart, brittle failure is a break with no stretch.
That bearing doesnt surprise me for the beating it was taking. It has always amazed me that some Dmaxes that break cranks could still run after the break. Break a crank on most other motors and you'd have parts scattering immediately from here to there....
It does seem like the smooth part was more a stress crack than the abrupt break of the tore part
Great pics.... Finally one that has the fracture surface that isn't wiped completely out, & someone that can take a picture:thumb:
Anywho, the crack starts in the rod journal fillet (bending fatigue maybe some tortional fatigue). The beach marks (fatigue fracture) radiate away from the crack initiation site (like ripples in a pool of water). These are slow growing cracks, very smooth. The rough part brittle, ductile (final fracture) part was just to weak to hold any more. I can't tell from the pics but you should be able to see Ratchet marks in the fillet where the crack began, with the beach marks radiating away. Last pic also shows what looks to be a possible inclusion very close the surface of the rod jouranl fillet, but could be just the lighting.
I have suspected improper grinding of the fillets on the crank. It makes no sense why some live at 1700 hp (Dimitri) and some die at stock power levels... Unless there is a issue with the manfacturing (finishing) of some cranks.
Anyone know if all the cranks are made at the same foundry & finished by the same machine shop?
Bhoward, you want to cut the broken ends off and send them to me? Anyone else that has a broken one that wants, can send it to me as well. Id like to get several of these together and compare... Maybe let some of the Cat guys take a look and help shed some light.
Anywho, the crack starts in the rod journal fillet (bending fatigue maybe some tortional fatigue). The beach marks (fatigue fracture) radiate away from the crack initiation site (like ripples in a pool of water). These are slow growing cracks, very smooth. The rough part brittle, ductile (final fracture) part was just to weak to hold any more. I can't tell from the pics but you should be able to see Ratchet marks in the fillet where the crack began, with the beach marks radiating away. Last pic also shows what looks to be a possible inclusion very close the surface of the rod jouranl fillet, but could be just the lighting.
I have suspected improper grinding of the fillets on the crank. It makes no sense why some live at 1700 hp (Dimitri) and some die at stock power levels... Unless there is a issue with the manfacturing (finishing) of some cranks.
Anyone know if all the cranks are made at the same foundry & finished by the same machine shop?
Bhoward, you want to cut the broken ends off and send them to me? Anyone else that has a broken one that wants, can send it to me as well. Id like to get several of these together and compare... Maybe let some of the Cat guys take a look and help shed some light.
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I dont know if Cat can look at them for failure analysis, but I could be wrong. Myt dealership won't look at any non Cat stuff.
Seems like that crank was being stressed at the failure point for a while, the waves are proof of continued stress such as a fatigue crack/material failure IMHO, not a extreme break of the crank.
Seems like that crank was being stressed at the failure point for a while, the waves are proof of continued stress such as a fatigue crack/material failure IMHO, not a extreme break of the crank.
Im the Failure Dude for my branch, it's my hobby
I'm not sending it to Cat. I know some of the Large Engine Engineers one of whom has a Metallurgy degree...
From the few good pictures I have seen, the fractures have been the same. Always starting in the fillet, Hint Hint....
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I would love to know the answers get burndown somw broken cranks. Also seems like they are more prone in lbz so did they switch mfgs. in 2006 or???? Dmitri has a lb7 that is maybe why his crank holds better plus im assuming it is balanced as much as possible:thumb: So my question is why lbz cranks?
My (Balanced) LLY crank broke. Bens (Duratothemax) crank that broke was also a LLY... I believe its a casting defect in certain cranks pretty much just luck of the draw be it a LB7, LLY, LBZ, etc, etc.... Mine also broke on a tow tune cruising through town at 40MPH....
My (Balanced) LLY crank broke. Bens (Duratothemax) crank that broke was also a LLY... I believe its a casting defect in certain cranks pretty much just luck of the draw be it a LB7, LLY, LBZ, etc, etc.... Mine also broke on a tow tune cruising through town at 40MPH....
Yes all have broke. It's hard to look at the fractures with picture... You really need to have the parts in hand or be able to look at them under a microscope.
I have seen no crank breakage as a primary failure at our shop on lb7 or LLY engines but I have seen around a dozen lbz and LMM failures. That to me says there is a MUCH greater likelihood of an lbz or LMM breaking, I have no concrete answers why but I wouldn't mind finding out.
Not really enough information there to make any kind of solid conclusion. It would be pretty neat if someone could compile as many variables as possible, such as model, mileage, power upgrades, towing habits, etc. I think it would be pretty interesting to see if any patterns surface.
I've been around a while and with my high degree of expertice in this , I can assure you every model year is plagued with this issue! It's all just bAD luck if yours breaks
and with my high degree of expertice in this , I can assure you every model year is plagued with this issue! It's all just bAD luck if yours breaks
Not sure what you mean. Looks 50-50 for breakage between the models. I don't think the power plays into as much as people think.
My LLY...
Any better pics? Something close and clear?