I had an all stock lmm snap one off with only 90000 on it. currently is getting a new motor put in it.
Broken Crankshaft Count?
- Thread starter EDP
- Start date
Honestly curious, but I'm guessing your's was still externally balanced yet, but did you have an AF cam?
I know it was a cheap shot, I apologize... I have a feeling he had other contributing factors also.
I believe the only true fix is the Winberg crank with the better filet and narrower rod journals to add meat and strength to the crank.
The reason I don't believe in the new stock crank theory is I have personally seen a LMM and a LML, both with under 70k miles, with full emissions and 100% stock with broken cranks... But we all know how piss poor the OEM balancing is, one Dmax will vibrate more than the next...
That's what I'm trying to determine.
I don't believe a new crank is the fix either. And stock new in stock dealer rebuilds are still breaking.
But the only way to accurately diagnose is to start with new parts. A used crank may be fine, and I don't knock anyone for using one, but there is no way to know how the past x amount of running time has affected it's integrity. Mag testing just checks the surface and I wouldn't solely rely on it's results. One could say you take the same risk with new, but I like to believe that new parts have no wear and no stressing on them plus hopefully passed a decent qc check.
It would be interesting to know the failure ratio between rebuilt with new crank and stock FO, rebuilt with used crank and stock FO, rebuilt with new crank and AF, and rebuilt with used crank and AF.
This info may be helpful to determine which route seems to work best or if it doesn't really matter at all.
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I don't believe a new crank is the fix either. And stock new in stock dealer rebuilds are still breaking.
But the only way to accurately diagnose is to start with new parts. A used crank may be fine, and I don't knock anyone for using one, but there is no way to know how the past x amount of running time has affected it's integrity. Mag testing just checks the surface and I wouldn't solely rely on it's results. One could say you take the same risk with new, but I like to believe that new parts have no wear and no stressing on them plus hopefully passed a decent qc check.
It would be interesting to know the failure ratio between rebuilt with new crank and stock FO, rebuilt with used crank and stock FO, rebuilt with new crank and AF, and rebuilt with used crank and AF.
This info may be helpful to determine which route seems to work best or if it doesn't really matter at all.
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to make that an accurate comparison, we would need to know the amout of trucks with used cranks or new that have NOT broke as well. find the percentage in each of broke vs not broke in new or used and compare them. otherwise looking at just who has broke what wont tell us much since there are far more used cranks being used since we started building engines vs guys using new cranks. atleast this is what i have seen over the years and i believe what you have seen as well.
Well I broke a brand new LB7 crank with std fire cam in 5k miles. My 70k used LBZ crank with AF cam has made it over 10k. The first build was around 800hp for 4k miles and the last 1k around 1,000hp. The current used LBZ crank engine has lived on a single tune that has been 1,000+HP the entire time and it sees that power pretty often lol. I'm hard on it. Both engines have had ATI dampners and balanced the same way from the sameachine shop.
I had a customer bring in a truck a couple of days ago complaining it was cutting out and missing driving down the road. The truck is a fully built motor that he just picked up from us 3 weeks ago after installing an alternate firing order cam for him; the truck idled fine and ran good as long as the RPM was below 2200 or so. If you tried to go above that, the tach would jump around and it would cut out like it was hitting a rev limiter. Turned out to be a broken crank. Makes me wonder if the crank was already damaged or if changing the firing order on a crank that has been previously used hard with a standard firing order can cause a failure. I doubt he even drove it 1000 miles before it failed.
The initiation points of the crank failures are off TDC by 20° after or more. While the the pattern still indicates primarily a bending failure there is a strong torsional component as indicated by the off TDC initiation point.
We switched a AF cam into our engine mid season last year after 65 hooks with a standard fire Hamilton. Ran the rest of season.
Reason why I sold all my dmax stuff. I broke the crank and was done with it.
http://www.duramaxdiesels.com/forum/showthread.php?t=61609
http://www.duramaxdiesels.com/forum/showthread.php?t=61508
http://www.duramaxdiesels.com/forum/showthread.php?t=49189
There's the threads from Fingers' section talking about the testing/analysis he's done on the cranks. I'd love to see you & him and you're contact and some engine builders together to see what you all could collectively figure out!!!
Exact same thing my buddy Dave experienced on his failure at 7hrs in the boat. Had I even considered the crank, I would told him to check that first rather than chase what sounded like an electrical issue. Thus trashing the block by reving it up then letting it idle while we data logged. I had no trained eyes on the engine either.
No rhyme, no reason, or anything short of hiring a Witch Doctor to remove the hex on this issue that I can think of to solve it. Just put two Billets on order, probably even have those blessed by a local priest for good measure.
:joker:
I was speaking with Ivan at Fluid Damper, who has those tools mentioned in my post above. They are located just outside Buffalo NY a few miles.
FD has an engine dyno setup with sensors to measure torsional twist at both ends using calibrated degree markings on a balancer and flywheel, compared to crank trigger signals. Along with some good ability to measure residence frequency off the block. What they haven't got into was tracking any cylinder pressure curves against this other data. IE, timing curve impacts.
If that's anything you might interested in pursuing, he said they would be willing to donate the time to study it further. I've only had time to skim over the data you've collected, but I feel Ivan might have some ideas worth exploring since FD has been studying this stuff some 30yrs. He has been tracking this thread also..
-K
eh no need to apologize when I rebuilt the motor I should have bought a new one or when aftermarket I also made the dumb move of putting a zf in the truck last year and who knows if south bend properly balanced the flywheel which i'm sure they didn't 5,000 rpm leaving the line isn't easy on parts just wish we found it earlier
Wish I would have known about this crank bs before I went from cummins to duramax. Love the truck but it makes me sick wonder if or when it will break