Broken Crankshaft Alt Fire Cam

[Burn Down]

To OP, out of curiosity what dampener and main size? I'm going to assume you used carillos? Who did your balancing? How did they remove material from the throw/counter weight. Could balancing be potential cause for a week crank?-not trying to bash you or your builder.

To anyone who knows more than me, are the glow plugs tuned with efi to fire with the AF cam or are they completely deleted?

You really need to go read all the broken crank threads and fingers threads on this topic...

Rest assured this is not something as simple as a balancing/machining issue.

 

[PACougar]

You really need to go read all the broken crank threads and fingers threads on this topic...

Rest assured this is not something as simple as a balancing/machining issue.

Or a glow plug issue:roflmao:

 

[Verlon at ATP]

I ran a 6480 cam last year on a new lb7 crank. I swapped to an alt fire 6480 this season on the same crank. Hope it goes well. My original lbz crank broke at the end of the 2013 season after 3 years running 800hp every where I went. 180k miles when it broke. Fingers crossed...

 

[NC-smokinlmm]

Or a glow plug issue:roflmao:

:roflmao:

 

[Cknight199]

Pulling my motor soon. Showing symptoms of a broken crank. 4500 miles on the motor, used my stock lbz crank (90k miles on it) and an alt firing cam. If it broke then it would have broken on a journal closer to the transmission since my balancer isn't wobbling.


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[DIESELMAFIAPER.LB7]

Are you ****in serious

 

[ty_LBZ]

I don't know if it's the engine balancing or the AF cam, but my engine runs smooth, even with Merchant motor mounts.

 

[Burn Down]

I don't know if it's the engine balancing or the AF cam, but my engine runs smooth, even with Merchant motor mounts.

Balancing... When we put Reece's engine back together from just a simple external balance you could literally stick a full glass of water on it and not spill a drop... I was blown away. I have heard with ALT. fire cams they feel even smoother.

 

[nwpadmax]

Duramax journal width is 2.260".

I was measuring the flat part where the rod bearings run on the pin. The length you have there must be to the outside of the fillets.

What's the proper way to specify the length? I'm not sure what conventions are used.

 

[nwpadmax]

For FEA, the "cheek to cheek" measurement is required for the Static model as well as the bearing contact width and location. The fillet plays in a great deal as far as the intensity of the stress riser. The "meat" at the break point is roughly the intersection of the crank and rod journal circles. So bigger journals or shorter stroke would improve the strength in the suspect area. Thickening the throw would help too, but there is no room in the block for the extra material.

So you're not missing anything.

BTW Matt, I bought the software.

So thinking out loud, just a sanity check....

Thicker throws would require either of the following:
1) narrowing the main bearing structures
2) narrowing the rod thickness at the journal

I know neither of these seem attractive.

The FEA comment was borne of a current situation at work. We have an issue that's 1/10 the complexity of this and has a full time PhD and an engineer working on it, and it's taking for friggin ever. I was really optimistic at first but now I'm wondering if they'll ever get it. And I feel like I'd get at it quicker with a pile of strain gauges and a datalogger...

Speaking of which....I would be really curious to see a datalog of the nose motion of the crank while running in a number of daily driving-type situations. I wonder if it's scarier than most people would expect.

 

[MarkBroviak]

So thinking out loud, just a sanity check....

Thicker throws would require either of the following:
1) narrowing the main bearing structures
2) narrowing the rod thickness at the journal

I know neither of these seem attractive.

The FEA comment was borne of a current situation at work. We have an issue that's 1/10 the complexity of this and has a full time PhD and an engineer working on it, and it's taking for friggin ever. I was really optimistic at first but now I'm wondering if they'll ever get it. And I feel like I'd get at it quicker with a pile of strain gauges and a datalogger...

Speaking of which....I would be really curious to see a datalog of the nose motion of the crank while running in a number of daily driving-type situations. I wonder if it's scarier than most people would expect.

I will put money on it that this is when the most damage is being done! It is when most are also failing and no load/light load from 1600-1800rpms is when I see the god-awful vibrations on the engine dyno with these motors. You can get it to "ring" when it does it! With the AF cams this vibration is drastically reduced. Stock cam makes the whole building shake and AF cam you only hear an audible sound. Combinations on parts alters it some but it is always in the same rpm window not matter what is tried.

 

[dirtydmax]

I will put money on it that this is when the most damage is being done! It is when most are also failing and no load/light load from 1600-1800rpms is when I see the god-awful vibrations on the engine dyno with these motors. You can get it to "ring" when it does it! With the AF cams this vibration is drastically reduced. Stock cam makes the whole building shake and AF cam you only hear an audible sound. Combinations on parts alters it some but it is always in the same rpm window not matter what is tried.

Do different balancers/dual cp3 loads on the front alter the vibrations through the rpm range?It's Interesting where the vibrations are seen.

 

[nwpadmax]

I will put money on it that this is when the most damage is being done! It is when most are also failing and no load/light load from 1600-1800rpms is when I see the god-awful vibrations on the engine dyno with these motors. You can get it to "ring" when it does it! With the AF cams this vibration is drastically reduced. Stock cam makes the whole building shake and AF cam you only hear an audible sound. Combinations on parts alters it some but it is always in the same rpm window not matter what is tried.

Any differences between internal vs external balance on standard cam?

Are both worse than AF?

I appreciate your reply above, Mark....thanks man.

 

[LBZ]

I will put money on it that this is when the most damage is being done! It is when most are also failing and no load/light load from 1600-1800rpms is when I see the god-awful vibrations on the engine dyno with these motors. You can get it to "ring" when it does it! With the AF cams this vibration is drastically reduced. Stock cam makes the whole building shake and AF cam you only hear an audible sound. Combinations on parts alters it some but it is always in the same rpm window not matter what is tried.

Cruising rpm on my truck on the highway with the 35's is right in this rpm range. I know the sound you are talking about and am not surprised that this is where I was running when mine broke. Good to know the AF does help alleviate some of this.

Because of where mine broke, behind the number 4 main, I am confident in the harmonics being the biggest issue.

The ones that break behind number 1 main I believe are from extra loading of the gear train (from dual CP3's, 2nd alternator, higher spring tension for the valves possibly, higher load from modified oil pumps/reliefs, Mitusa pumps, etc), possibly bad dampners, and harmonics all combined. Or even individually plus harmonics alone.

Again, sucks to hear of a couple breakages with the AF cam, but I digress, without starting with new parts, it's tough to point the finger at one thing or the other. If the only parts changed after a breakage were the crank and cam, this would be the ideal scenario for a proper test. And the more done this way, the better the range of info is that can be gathered from future failures-or non failures even.

Need more of them out there with new cranks in DD's to get a better idea if it helps or not IMO.

 

[S Phinney]

The only things I will be changing this time will be new crank, different cam and internal balance. Everything else will be the same. Maybe it was just a fluke. I would feel much better if it were.

 

[Fingers]

So thinking out loud, just a sanity check....

Thicker throws would require either of the following:
1) narrowing the main bearing structures
2) narrowing the rod thickness at the journal

I know neither of these seem attractive.

The FEA comment was borne of a current situation at work. We have an issue that's 1/10 the complexity of this and has a full time PhD and an engineer working on it, and it's taking for friggin ever. I was really optimistic at first but now I'm wondering if they'll ever get it. And I feel like I'd get at it quicker with a pile of strain gauges and a datalogger...

Speaking of which....I would be really curious to see a datalog of the nose motion of the crank while running in a number of daily driving-type situations. I wonder if it's scarier than most people would expect.

Thicker throws would require narrowing the main caps and shaving the block.

Narrowing the rod gets into narrowing the bearing since the bearing has to be offset from the fillet and centered to the thrust from the rod The mid rod thickness could be maintained by only thickening the throw in the problem area at the rod journal.

A good FEA is a wonderful tool, but you have to use it correctly. I'm no Phd, granted, but I've been working this problem on and off for about a year and a half with the software. I almost always come back to just a validation of the original design.

I feel that IF I could get good quality motion data off of a crank, especially one shaking like Mark describes, I could zero in on the source. I just don't have the cash to spend at this time.

 

[Smokum]

Thicker throws would require narrowing the main caps and shaving the block.

Narrowing the rod gets into narrowing the bearing since the bearing has to be offset from the fillet and centered to the thrust from the rod The mid rod thickness could be maintained by only thickening the throw in the problem area at the rod journal.

A good FEA is a wonderful tool, but you have to use it correctly. I'm no Phd, granted, but I've been working this problem on and off for about a year and a half with the software. I almost always come back to just a validation of the original design.

I feel that IF I could get good quality motion data off of a crank, especially one shaking like Mark describes, I could zero in on the source. I just don't have the cash to spend at this time.

I'll ask the stupid question - what kind of cash would it take? And when you say motion data, I assume on a dyno would work (meaning you wouldn't have to be actually going down the road)?

 

[Cknight199]

Are you ****in serious

Will know more over the weekend

I don't know if it's the engine balancing or the AF cam, but my engine runs smooth, even with Merchant motor mounts.

Balancing... When we put Reece's engine back together from just a simple external balance you could literally stick a full glass of water on it and not spill a drop... I was blown away. I have heard with ALT. fire cams they feel even smoother.

My motor ran much smoother with the cam at idle, even my builder said he loved how smooth mine was compared to others with stock cams that he has done.



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[CaptPhil]

That sucks man, hope it isnt broken.

Now im all worried about my crank, haha. Stock cam and all.

I guess having a 5 speed is better in that my cruising rpm is very very rarely under 2k rpm, which should keep me out of the vibration zone.

 

[WVRigrat05]

I wondered about that 6th gear with the rpm range causing an issue, I leave mine in 5th unless I'm over 85 mph With the 35's.