Broken Crankshaft Count?
- Thread starter EDP
- Start date
No direct experience, but I have heard that internally balancing a stock crank is very dodgy because you have to remove so much metal from the counterweights that there's very little "meat" left.
One guy I know was pursuing a billet crank for this reason, with counterweight dimensions that would better accommodate the heavy metal slugs.
But I'm sure there's more than one way to skin a cat.
One guy I know was pursuing a billet crank for this reason, with counterweight dimensions that would better accommodate the heavy metal slugs.
But I'm sure there's more than one way to skin a cat.
I have scene Internally balanced, hammer out mains, create cap walk all just as fast as a stock non cryoed simple balanced rotating assembly fail.
I have also scene and heard of many stock LBZ and LMM's fail in stock truck form from 20,000k all they way up to 180K.
We did some research on stock cranks un alltered and never scene anything but stock tunning on stock rotating parts and lets just say there is not much attention given to balancing stages at the duramax plant.
Many would be amazed at how long a dmax crank will live with small breaks at a time and how they may not even know its broke.
Recently had a guy chase his tail on a LBZ for 8,000miles with random crank pos sensor code. Every once in awhile truck would gallop at a stop light and then trip the code. Replaced sensor twice and finally said heck with it. Continued to drive and tow everyday until one day she let go all the way on a shut down and would not fire back up after shut down. Truck still cranked over fine but acted like it was out of fuel. towed it to a shop they flushed the fuel system and then found out the crank had broke completly in half.
Some of these crank failures you will see break lines through out the whole crank all the way through similar to looking at an old tree and counting its rings.
If I was going to push the limits past 1200hp and runn excessive RPM I would still debate on spending the money on internally ballancing the motor at this time. Would it hurt the LIFE of the motor or crank and take away from its strenght or integrety No NOT if it was properly done.
i never expected to see such a wimpy crankshaft in a diesel. the counterweights are narrower than a sbc crank, which is where mine broke (thru the counterweight) its odd to me how some guys push so much power through a stock crank yet half the broken ones are in a sub-500rwhp truck. mine was stock. this makes me think it was a flaw or something like that on some of the cranks out there.
i just purchased a 2ft. machinists' straight edge to check the mains on my block. im going to try to flip the engine upside down and swap a new crank in with new bearings/bolts. the front main bearing didnt spin in its bore when the crank broke so im hoping the block might be ok.
i just purchased a 2ft. machinists' straight edge to check the mains on my block. im going to try to flip the engine upside down and swap a new crank in with new bearings/bolts. the front main bearing didnt spin in its bore when the crank broke so im hoping the block might be ok.
Does anyone believe that tuning is a primitive factor in determining the longevity of these cranks?
So would you say X-ray, Shotpeen, or Stress Relief measures be possible on this crank before deciding to install without the Xray for instance. Seems like small defects might show internally the point is it appears the cranks that Isuzu gets from Sumotomo in Japan must have inferior grades of metal or contamination if they are breaking and cracking as above descriptions read. Sure causes one to use tools of the analysis available if you are putting one together. Hell check the crank if it's out is maybe the thing to just do. Many engines make hi miles but these defects seen and reported are worth watching if you want to keep your truck after using it hard. The best way is to listen to the ones who see the start pts. of defects.
I have heard of broken "billet" cranks, and stroker cranks... So balance must have somewhat of a contributing factor.
broken crank
I live in Alberta Canada. First time post. This my second Dmax 1st was 2003 and had about 550,000 km and then burnt to the ground. My current on is 07 classic 3500 with 475,000 km & the crank broke. Dont have it apart yet but looks like back of the crank. Can a crank be replaced without doing any other work? Someone told take it out turn it upside down & replace it. I have run diesel for over 12 yrs. outside of injectors on earlier ones no real issues
I live in Alberta Canada. First time post. This my second Dmax 1st was 2003 and had about 550,000 km and then burnt to the ground. My current on is 07 classic 3500 with 475,000 km & the crank broke. Dont have it apart yet but looks like back of the crank. Can a crank be replaced without doing any other work? Someone told take it out turn it upside down & replace it. I have run diesel for over 12 yrs. outside of injectors on earlier ones no real issues
One more for the broken crank club
Hay guys I Have a 2007.5 LMM 2500HD with 220000k and broke the Crank after the first journal just like most all the other ones I have seen on line
After pulling the moter I noticed that one of the keys that hold the timing gear in place has been sheared off! I thought from the crank failure at first, but am now leaning towards the cause of the failure. Thoughts??? When it broke I was driving 90kph my oil pressure stayed normal no engine light on
at first I could hear a light drone coming from the front of the engine I pulled over not knowing what was to come, and looked around under the hood. Nothing! Let her cool down for 30 min than started on my way back. After a few min the drone turned in to tick,tick,tick.... It would come and go. Thinking I had broken my flex plate I took it easy and tried to make it home. Full power good throttle response no change in engine minus the tick,tick I drove for about 45 min then she let go tick,tick,click,click then bang. I almost instantly shut her down and coasted off to the shoulder. Towed her home that's where the fun starts.... all the locals hear Duramax and see $$$$ wtf I was told everything was trashed bent connecting rods smashed pistons into the heads cracked block bent valves they tried there best to tell me she wouldn't ever run agin.... But they didn't know that when I towed her home, the next day thinking I had a broken flex plate I went and fired her up!!!! she ran clunky well more than clunky but she ran! They don't run after everything bent,cracked and smashed into everything else! just sayin I have many pics if anyone would like to see! Now its been 2 months+ without my truck I'm in need of a crank that I can afford not a 4500$ one! btw everything survived I magnafluxed the block pressure test the heads pistons and rods all pass no bent valves! She will live agin!!! I know there is more people out there with this problem (broken crank) to all of you, POST! We will be seeing much more of this as time goes by I'm sure thanks for reading sorry for rambling lol
Hay guys I Have a 2007.5 LMM 2500HD with 220000k and broke the Crank after the first journal just like most all the other ones I have seen on line
After pulling the moter I noticed that one of the keys that hold the timing gear in place has been sheared off! I thought from the crank failure at first, but am now leaning towards the cause of the failure. Thoughts??? When it broke I was driving 90kph my oil pressure stayed normal no engine light on
at first I could hear a light drone coming from the front of the engine I pulled over not knowing what was to come, and looked around under the hood. Nothing! Let her cool down for 30 min than started on my way back. After a few min the drone turned in to tick,tick,tick.... It would come and go. Thinking I had broken my flex plate I took it easy and tried to make it home. Full power good throttle response no change in engine minus the tick,tick I drove for about 45 min then she let go tick,tick,click,click then bang. I almost instantly shut her down and coasted off to the shoulder. Towed her home that's where the fun starts.... all the locals hear Duramax and see $$$$ wtf I was told everything was trashed bent connecting rods smashed pistons into the heads cracked block bent valves they tried there best to tell me she wouldn't ever run agin.... But they didn't know that when I towed her home, the next day thinking I had a broken flex plate I went and fired her up!!!! she ran clunky well more than clunky but she ran! They don't run after everything bent,cracked and smashed into everything else! just sayin I have many pics if anyone would like to see! Now its been 2 months+ without my truck I'm in need of a crank that I can afford not a 4500$ one! btw everything survived I magnafluxed the block pressure test the heads pistons and rods all pass no bent valves! She will live agin!!! I know there is more people out there with this problem (broken crank) to all of you, POST! We will be seeing much more of this as time goes by I'm sure thanks for reading sorry for rambling lol
GM Parts cheap has a new GM crank listed for right at $1000.
Talk to Guy at SoCal, or Henry at Creatures of the Night-I'm sure that there are others out there. They may have or know someone who has a good used crank.
I'm still of the belief it has more to do with production errors in the method of forging and heat treat than anything else. This opinion is based on the large number of stock, or nearly stock engine failures, and the number of "stupid torque" builds that survived. When an engine that sees 3-4 times the stock torque survives, it makes you think. If the design itself was the problem, you have nearly complete failure at double the torque. ie - 1% of a spool of chain breaks lifting a 5000lb load, putting 10,000lb on it would show huge failure rates if the chain was uniformly made. Putting 20,000lb on it should be instant death. That is unless 1% of the time the machine forgets to weld a link together, then the death rate would stay the same.
These are rotary forged. The forge it planar, then index it.
These are rotary forged. The forge it planar, then index it.
I just broke my 2nd one today, I got 28000 miles on a new GM crank,,, that's not bad...
Last edited:
I just broke my 2nd one today, I got 28000 miles on a new GM crank,,, that not bad...
You cant catch a break can you
Sorry to hear that.
Man o man is this common. Can't believe I didn't hear to much of this earlier. Hope the hell mine stays together for awhile longer. Saving for a motor build but still sweatin the trans, twins, injectors, manifold and up pipes I bought. Can't even imagine havin to build motor right away. I would cry. Lol
