Broken Crankshaft Count?
- Thread starter EDP
- Start date
Figured it out huh? So what's the problem?
The early duramax had 17.2:1 also then went down to 16.8:1.
While idk if that intake balance is the cause, that sure is a great idea. Good catch. While your on that, have you noticed the left side exhaust manifold? It's also pinched to "clear the steering shaft"
And the cylinder balance cancels after 1000rpm
The cranks breaking comes down to engine design and overall rotating weight. If GM had made the engine 1 to 1.5 inches longer they cold have designed the crank with more meat in the radius filets. There is not enough there to handle the overall stress placed on it. Nothing is indestructible but design in itself is where the problem falls.
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Are the breakages related to HP? (More common with modded trucks?)
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Seen it both ways modded and stock. Modded more common....yes
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So the question remains, why do some stock trucks break them at 150k, some stocks trucks last 400k+, some guys make 800+hp for years and never break one and the next guy does a build and breaks a crank in 6 months?
Because each crankshaft is not created equal. I have had each extreme myself. I have had two cranks break and have had a truck go 450k and still going strong.
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I would agree with Shane and say that goes for everything made on this planet. There are no 2 identical parts, everything is slightly different. Yes standards and testing is in place but it always will be ever so slightly different...part of the human factor that will never be overcome. But that's my opinion obviously
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That's not too terrible of an expectation is it? Hard life to nearly half a million miles before it had a catastrophic failure? I think I could be ok with that - "I ain't mad at it" 
That's really good imo. If my truck makes it to 420xxx ill be impressed
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At the rate I drive, about 12,000 miles, by the time I'm 80 years old, I'll have 650,000 miles. Hardly tow and truck is stock. Should never need another vehicle, ever. If the crank brakes, I'll rebuild the engine and keep the truck.
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Mark down the first one known to break in a boat...
Buddy Dave verified his LMM crank is broken today. I swore he had an electrical misfire issue by the way it just started missing. Nope, it's broke near the damper somewhere. Is a compound motor with under 10hrs since build. Probably was making 650 flywheel HP when it let go under 4000R's..
Buddy Dave verified his LMM crank is broken today. I swore he had an electrical misfire issue by the way it just started missing. Nope, it's broke near the damper somewhere. Is a compound motor with under 10hrs since build. Probably was making 650 flywheel HP when it let go under 4000R's..
Mark down the first one known to break in a boat...
Buddy Dave verified his LMM crank is broken today. I swore he had an electrical misfire issue by the way it just started missing. Nope, it's broke near the damper somewhere. Is a compound motor with under 10hrs since build. Probably was making 650 flywheel HP when it let go under 4000R's..
Stock cam i presume?And only 10 hrs on a fresh build is scary.If my fresh motor breaks one im done.Sorry to hear and hope its not too bad.
Mark down the first one known to break in a boat...
Buddy Dave verified his LMM crank is broken today. I swore he had an electrical misfire issue by the way it just started missing. Nope, it's broke near the damper somewhere. Is a compound motor with under 10hrs since build. Probably was making 650 flywheel HP when it let go under 4000R's..
Where is Dave from? We did a twin kit for an LMm in a boat about 6 months ago... Sorry to to hear..
Yeah it was a stock cam engine. Rods, 15.5:1cr pistons, and ATI damper for those keeping track.
Boat has a Arneson surface drive connected to a 6sp Allison without a converter. Been working out some bugs with the shifting speeds, but nothing strange to speak of happened. Have plenty of video and data logs from this new engine over that 10hr period. Bumped high RPM timing up to +30 couple weekends back to lower EGT's, that's about it.
He was just getting on plane around 60% throttle when noticed a slight miss. Got worse quick and set bunch of codes. Should also be noted that when it shifts 4-5 the prop would cut loose and you could see that in the output shaft speed in data logs. So not like being hooked to sled or anything heavy loaded. I had actually commented that his engine load readings were too low, like 45% at 70% throttle. Max RPM I have seen logged is 3900.
Central CA. Probably same boat. He switch the stock VNT to a 4094R with this new build and she had been running great.
Boat has a Arneson surface drive connected to a 6sp Allison without a converter. Been working out some bugs with the shifting speeds, but nothing strange to speak of happened. Have plenty of video and data logs from this new engine over that 10hr period. Bumped high RPM timing up to +30 couple weekends back to lower EGT's, that's about it.
He was just getting on plane around 60% throttle when noticed a slight miss. Got worse quick and set bunch of codes. Should also be noted that when it shifts 4-5 the prop would cut loose and you could see that in the output shaft speed in data logs. So not like being hooked to sled or anything heavy loaded. I had actually commented that his engine load readings were too low, like 45% at 70% throttle. Max RPM I have seen logged is 3900.
Central CA. Probably same boat. He switch the stock VNT to a 4094R with this new build and she had been running great.