LBZ: Broke my crank

B

Bryce418

Still slow
Oct 5, 2009
611
0
0
Burn Down said:
Caterpillar likes to do the same. No one wants to admit they blew it...:D
Click to expand...

I hear ya loud and clear there, we're also a teps dealer, so I have gotten my fair share of the yellow treatment.
I also have Isuzu to contend with, so I have received plenty of fertilizer over the years.
 
M

Michael

ISSPRO Engineering Mgr
Feb 17, 2009
77
0
0
Happy Valley, OR
Has anyone tried turning the crank down and increasing the fillets in the mains in the process? I know that would raise other issues with the hardened layer on the crank bearing surfaces, possibly requiring re-treating, but it seems like it might be worth it if it solves this breakage issue. I'll have "spare" LBZ & LB7 cranks from my current build (planning to use an LB7 crank and have another that needs grinding), if I have any issues with the first LB7 crank I may try this out.
 
Gasuout

Gasuout

Johnny
Mar 20, 2008
2,188
0
0
Santa Ana , Ca.
My ? is .... :thinking2:

How many of these failures have had a balancer shear the pin in the past and spin the balancer on the crank ?

I have a crank here LB7 .... that is broke at 2nd journal and it sheared the pin and spun the balancer . Its from the block I am using now .

Very common for a dmax to break the crank in this situation with a spun balancer .

I spun a balancer on my new motor shortly after the build .... dealer left the crank bolt loose after doing a water pump . That was the ultimate SUCKY DEAL ! .... fresh motor all balanced and you shear a crank pin due to neglagence from another . Sheared it on the throttle in 4th gear ..... shook like a son of a bitch . So much for a socalled balanced motor . :D

Always in the back of my mind ... fatigue from this in the past .

BHOWARD .... so sorry to hear your luck brother . Hadnt heard you broke the truck . So how is the new motor coming along ?
 
BHoward6.6

BHoward6.6

West Coast
Feb 9, 2011
274
0
16
Huntington Beach, CA
Gasuout said:
My ? is .... :thinking2:

How many of these failures have had a balancer shear the pin in the past and spin the balancer on the crank ?

I have a crank here LB7 .... that is broke at 2nd journal and it sheared the pin and spun the balancer . Its from the block I am using now .

Very common for a dmax to break the crank in this situation with a spun balancer .

I spun a balancer on my new motor shortly after the build .... dealer left the crank bolt loose after doing a water pump . That was the ultimate SUCKY DEAL ! .... fresh motor all balanced and you shear a crank pin due to neglagence from another . Sheared it on the throttle in 4th gear ..... shook like a son of a bitch . So much for a socalled balanced motor . :D

Always in the back of my mind ... fatigue from this in the past .

BHOWARD .... so sorry to hear your luck brother . Hadnt heard you broke the truck . So how is the new motor coming along ?
Click to expand...

It's coming, gona be about 3 weeks.
 
zeke38

zeke38

New member
Sep 29, 2009
172
0
0
33
Newark, IL
Lbzs be breaking cranks!

165114_1670595199542_1077222637_31827413_2995347_n1.jpg
 
BHoward6.6

BHoward6.6

West Coast
Feb 9, 2011
274
0
16
Huntington Beach, CA
As far as I know, (not far) all the cranks break at the #2 main. I thought it was from all the weight hanging out on the harmonic balancer, combined with the not very well balanced rotating assembly.
That theory goes down hill fast with my crank broke at the #4.
 
Burn Down

Burn Down

Hotrodder
Sep 14, 2008
7,092
28
48
Boise Idaho
I'm kind of with Michael, I think it has something to do with the fillets. Improper finish, wrong dimensions or a combo of things... Need lots of broken parts to look at, inorder to make determination.

Zeke, still have your crank?
 
M

mainer

New member
Nov 11, 2008
326
0
0
Add another broken crank to the list, my buddy just broke one in his 04 lb7.

completely stock truck, 120k on it.

only thing i can relate to this break is that last summer he lost injectors and filled crankcase with fuel, probably washed the bearings pretty good, but it had been running fine ever since new injectors. Havent gotten the motor out but the balancer is wiggling around. Truck still runs though.
 
adeso

adeso

wait, what?
May 30, 2011
1,569
0
36
Minot, ND
How much clearance did you have set in your mains? stock? Did you ever mag test the crank?
This is one of my nightmares...
 
adeso

adeso

wait, what?
May 30, 2011
1,569
0
36
Minot, ND
I have been told that they like to set the mains at 0.003-0.0035 or high HP trucks will push the mains out. I have mine set at around 3 thousands and 2 tenths (0.0032). I also hear of most of the cranks breaking while just driving down the road after the stress crack grows to much, makes me wonder if something isn't going on with harmonics??? I'm just guessing here

Edited for mistype on cleanace
 
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BHoward6.6

BHoward6.6

West Coast
Feb 9, 2011
274
0
16
Huntington Beach, CA
Burn Down said:
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.
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Burn Down,
I have the crank out and going to cut the broke section out today. P.M. me your address and I will send them to you.:hug:
 
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