Duramax Diesels Forum Truck of the Week
  #31  
Old 02-11-2015, 01:30 PM
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Its a very interesting subject for sure, would be nice to know exactly why.

And a side thought, if I built my engine there's no way I'd bother buying a new crank if mine checked out ok. Too many guys breaking new ones, even under moderate power!

It is still a fairly common practice for racers to run a "seasoned" bottom end in their cars. Basically run your bottom end for the racecar next year, in the tow vehicle this year. Doesn't explain why people break them on old cranks, but maybe guys with brand new are pushing them too hard right out of the gate.

And IMO I wouldn't do an AF cam with a used crank. Unsure of how changing the firing order would change the stresses halfway through a cranks life?

Sorry for the clutter
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  #32  
Old 02-11-2015, 08:22 PM
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Originally Posted by NC-smokinlmm View Post
Is thre any connection to this and the tick knock? I know that every Duramax dosen't have it and those that do have different variations of what it sounds like. I've never heard any other diesel ever do it, just the Duramax. Anybody ever make a correlation to it and broken cranks?
Mine had this for the first 40 000 miles then it went away for the most part. Once in awhile it would do it after that. Then I broke a crank at 120000 miles.........Is there a connection? Maybe...
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  #33  
Old 05-19-2015, 02:21 AM
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Something I never put out there is that the force on the crank to make the variations that you are seeing in these plots is on the order of 40,000 ftlbs if the whole crank is actually being accelerated/decelerated the shown amount.

I don't think that is the case. Because of twist, not nearly as much of the crank's inertia is coming into play. Probably on the line of 1/4 of the inertia, so say 10,000 ftlbs which translates to about 60,000 lbs on the rod journal.

That seems like a lot, but each piston and rod pushs on the journal with 25,000 to 30,000 lbs cruising down the highway.

Bottom line is the velocity changes are significant and need to be looked into in more detail with better measuring techniques.
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  #34  
Old 06-02-2015, 12:55 PM
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Originally Posted by Fingers View Post

So on a whim, I changed my basis for the plots from crank degrees, to time. This allowed me start to see a frequency relation between the crank speed variations. If I run through the data frames as the engine revs up, you can see the variation amplify and recede and amplify. The waves seem to be certain frequencies. In my engine's case, about 188HZ, but I have data for others that indicate other frequencies for those engines.

I am still not sure where the driving input is coming from, but it is clear to me that when it lines up with the natural harmonic of the crank, it amplifies.

I also notice a fair bit of variation from engine to engine. In my case, the natural frequency changed from one build to the next.
Have you had a chance, John, to test again with a viscous damper and see if it eliminated that frequency or shifted any of the frequencies at all?
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  #35  
Old 06-02-2015, 01:31 PM
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Quote:
Originally Posted by Fingers View Post
Something I never put out there is that the force on the crank to make the variations that you are seeing in these plots is on the order of 40,000 ftlbs if the whole crank is actually being accelerated/decelerated the shown amount.

I don't think that is the case. Because of twist, not nearly as much of the crank's inertia is coming into play. Probably on the line of 1/4 of the inertia, so say 10,000 ftlbs which translates to about 60,000 lbs on the rod journal.

That seems like a lot, but each piston and rod pushs on the journal with 25,000 to 30,000 lbs cruising down the highway.

Bottom line is the velocity changes are significant and need to be looked into in more detail with better measuring techniques.

I believe I mentioned that same thing in the other thread you started a year ago. Several times actually. But got ignored and or deleted.
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  #36  
Old 06-02-2015, 03:06 PM
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Quote:
Originally Posted by juddski88 View Post
Have you had a chance, John, to test again with a viscous damper and see if it eliminated that frequency or shifted any of the frequencies at all?
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  #37  
Old 06-02-2015, 09:13 PM
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Stock and ATI only so far for dampeners. I don't think a dampener has enough mass to smooth this out. Look at the scale of the fluctuations. 10% in some cases. You would need an additional 20# mass to even dent that.

Still looking for the source.
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Danville 68mm VVT Turbo
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Last edited by Fingers; 06-02-2015 at 09:24 PM.
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  #38  
Old 06-02-2015, 09:20 PM
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Quote:
Originally Posted by Dave c View Post
I believe I mentioned that same thing in the other thread you started a year ago. Several times actually. But got ignored and or deleted.
Try to ride that high horse again, and the same thing will happen again.
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'04.5 EC/LB 4x4.
Howard Rods w/ oiler hole.
Oval Chambers and valve reliefs cut in Mahle Cast Pistons. 17.5:1
SoCal Stage 2 heads, 3388 Cam, Billet Flywheel, and harmonic balancer.
Danville 68mm VVT Turbo
100 over injectors.
PPE Dual CP3s
ProFab Castflow headers and uppipes.
100 PSIA MAP Sensor
Kennedy dual lift pump.

Dynoed 690 HP / 1200 TQ
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  #39  
Old 06-03-2015, 06:34 AM
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Quote:
Originally Posted by Fingers View Post
Stock and ATI only so far for dampeners. I don't think a dampener has enough mass to smooth this out. Look at the scale of the fluctuations. 10% in some cases. You would need an additional 20# mass to even dent that.

Still looking for the source.
Would we? Assuming that the Alt. Firing order reduces that 10% change in velocity even by half, and that it is not the entire cause for the cranks to start cracking, but instead a contributor, maybe we add some rotating mass to the damper and also find a way to dampen the wave that could be weakening the material at that journal?

Edit: Also, because the viscous dampener may dampen a wider range of frequencies, the extra-mass theory may not hold true. The ATI dampener is really only tuned to dampen one natural frequency at a given velocity, not multiple.
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Last edited by juddski88; 06-04-2015 at 05:13 AM.
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  #40  
Old 10-31-2015, 06:01 PM
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Anything new on this ?
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  #41  
Old 12-03-2015, 09:30 PM
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Finally got around to making a tone wheel for the front of the crank. It has the same tooth count as the starter gear. It will attach, via a hub, to the middle of the harmonic balancer.

Using a prox sensor, like the one on the crank reluctor, I should be able to compare the front and back crank signals with a scope. Any phase shifting will show up as the signals getting out of phase.

I had done something similar using just the build in crank sensor, but the tooth count difference meant I had to use software to pull anything useful out of the data.

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But.....What do I know.

'04.5 EC/LB 4x4.
Howard Rods w/ oiler hole.
Oval Chambers and valve reliefs cut in Mahle Cast Pistons. 17.5:1
SoCal Stage 2 heads, 3388 Cam, Billet Flywheel, and harmonic balancer.
Danville 68mm VVT Turbo
100 over injectors.
PPE Dual CP3s
ProFab Castflow headers and uppipes.
100 PSIA MAP Sensor
Kennedy dual lift pump.

Dynoed 690 HP / 1200 TQ
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  #42  
Old 12-03-2015, 09:43 PM
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Deadly!!

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  #43  
Old 12-04-2015, 05:29 AM
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Glad to see you still working on this. My crank scares me every time I go WOT
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  #44  
Old 12-04-2015, 08:00 AM
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I'd expect to see some deceleration/acceleration on each firing stroke if your resolution was great enough. That signal makes no sense.
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  #45  
Old 12-04-2015, 08:13 AM
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Nice Jon!!!
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