Broken Crankshaft Count?
- Thread starter EDP
- Start date
First off, thanks Mark for sharing that info, I always suspected it was harmonics that were playing a factor into this and this adds to my theory.
Second, you guys can't point at one crank that broke and say "that proves X" it was one crank, and you have no clue that could have been the one that had a defect and was going to break no mater what. So before I believe and link does or does not exist I need to see a trend with multiple cases unless there is hard evidence that the item in question caused the issue.
If my theory is correct, something has to be done to take the part out of its natural frequency range that is causing the harmonic event. In something as complex as an engine, the parts interact with each other in a very very complex way. Damping it externally (ie motor mounts) isn't going to fix it unless it changes the natural frequency of the block and that is feeding it (but I don't think that is what is causing it, I think something internally). Something as simple as an alt fire cam might work, lower compression might be working, there is a good chance something is going on with the combustion at those RPMs that is exciting it that you would never see just by balancing the rotating assembly.
I'm just spitballing here with ideas but really until someone puts some measuring equipment on an engine on a dyno and tries different things until we find something that really changes the range of these events we are just guessing. And who knows, maybe it is a combination of a harmonic event with a load on the front of the crank, maybe (probably) hooking a torque converter up will change it as well.
Second, you guys can't point at one crank that broke and say "that proves X" it was one crank, and you have no clue that could have been the one that had a defect and was going to break no mater what. So before I believe and link does or does not exist I need to see a trend with multiple cases unless there is hard evidence that the item in question caused the issue.
If my theory is correct, something has to be done to take the part out of its natural frequency range that is causing the harmonic event. In something as complex as an engine, the parts interact with each other in a very very complex way. Damping it externally (ie motor mounts) isn't going to fix it unless it changes the natural frequency of the block and that is feeding it (but I don't think that is what is causing it, I think something internally). Something as simple as an alt fire cam might work, lower compression might be working, there is a good chance something is going on with the combustion at those RPMs that is exciting it that you would never see just by balancing the rotating assembly.
I'm just spitballing here with ideas but really until someone puts some measuring equipment on an engine on a dyno and tries different things until we find something that really changes the range of these events we are just guessing. And who knows, maybe it is a combination of a harmonic event with a load on the front of the crank, maybe (probably) hooking a torque converter up will change it as well.
Anybody ever think the Duramax tick knock might be associated with this? I know it is the result of an oil film condition at the crank? Just throwing it out there for the guys who understand harmonics to ponder bc I sure don't...
I agree, it is a combination of things that is causing the end outcome of the failures. Every piece of metal has a frequency that will cause it to vibrate to the point of self destruction and it appears we are causing this to happen. Changing small pieces of the puzzle seems to affect it but a clear cut answer is not proven yet. I think the motor mount info was taken the wrong way here. I didn't mean that it had anything to do with any of the issues or a help in the fix. I meant that with them installed the vibration from the motor was a lot more noticeable than on the stock mounts. I would like to do a scientific harmonics test in a truck with a back to back cam change from stock to an AF stock cam to see the difference in harmonics and or where/what changes with it. Like I said, time will tell but so far so good.
I wonder how many cranks have broke in trucks with filled blocks? Would that dampen the harmonic vibration or make it worse?
quite a few people have filled blocks and broken cranks...mostly pullers I know of, but the crank I would think needs to be looked at as a separate harmonic event from the block, since they are not directly touching one another...ideally 
quite a few people have filled blocks and broken cranks...mostly pullers I know of, but the crank I would think needs to be looked at as a separate harmonic event from the block, since they are not directly touching one another...ideally
Agreed, unless it is some how affecting it but how do we determine that without a back to back comparison.
I need to find smaller versions of the vibration monitors that we have in our Solar turbines
We also trend bearing temps which would be amazing to have in a Comp engine
http://www.ge-mcs.com/en/bently-nev...nd-velocity/330500-piezo-velocity-sensor.html
Mounting would be near impossible for something like this, but maybe there are smaller products out there.
Maybe too small: www.youtube.com/watch?v=Tx5vvMxMna
These guys have some cool RTDs: http://www.thermometricscorp.com/bearing-sensor.html
We also trend bearing temps which would be amazing to have in a Comp engine
http://www.ge-mcs.com/en/bently-nev...nd-velocity/330500-piezo-velocity-sensor.html
Mounting would be near impossible for something like this, but maybe there are smaller products out there.
Maybe too small: www.youtube.com/watch?v=Tx5vvMxMna
These guys have some cool RTDs: http://www.thermometricscorp.com/bearing-sensor.html
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I've done the vibration sensing. Doesn't tell the source per se. Only that the engine is shaking in time with the crank rotation. (duh) Sensing on the block is decoupled from the crank enough that you are not getting a good correlation between the crank event and the block movement.
So, only when the crank vibration is in harmony with the block's harmonic do you see the block shake violently. The Crank itself could be vibrating at several points, or through the whole spectrum and you would only see the block shake when they align.
So, only when the crank vibration is in harmony with the block's harmonic do you see the block shake violently. The Crank itself could be vibrating at several points, or through the whole spectrum and you would only see the block shake when they align.
which is why unfortunately the only real way to attempt this would be imho is to have an engine on a dyno and do some runs, and start changing things until you notice a big change in vibrations. And even then harmonics is just a theory it could be combined with something else like the cam gear loading.
Harmonics isn't a theory. They are there. You can feel and hear them in some cases and they have been measured.
Question is how are they being generated and what are the best ways to reduce them? Cam loading for instance does not explain breaks in the middle of the crank. However does the cam loading induce additional harmonics through the gear train into the crank?
Too many unknowns I agree, but it seems the steps being taken so far seem to indicate an improvement.
Like someone else said about the 6.5's that used to break cranks didn't change much in design but the use of better dampner's reduced the failures.
Question is how are they being generated and what are the best ways to reduce them? Cam loading for instance does not explain breaks in the middle of the crank. However does the cam loading induce additional harmonics through the gear train into the crank?
Too many unknowns I agree, but it seems the steps being taken so far seem to indicate an improvement.
Like someone else said about the 6.5's that used to break cranks didn't change much in design but the use of better dampner's reduced the failures.
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http://www.agcoauto.com/content/news/p2_articleid/273
This is a fairly simplified description of how harmonics work and why the balancer is important. I think the cranks break because the harmonics are exceeding the amount the balancer is designed to dampen. That and the added weight and stress on the front with not enough bearing support area causes the #1 failures. The failures in the middle and closer to the rear I believe are caused by the harmonics and torsional stress alone. At cruising rpm in my truck, I could really feel it.
This is a fairly simplified description of how harmonics work and why the balancer is important. I think the cranks break because the harmonics are exceeding the amount the balancer is designed to dampen. That and the added weight and stress on the front with not enough bearing support area causes the #1 failures. The failures in the middle and closer to the rear I believe are caused by the harmonics and torsional stress alone. At cruising rpm in my truck, I could really feel it.
Sound is nothing more than vibration. Considering the Duramax "tick" is audible it would seem that it's a vibration/harmonic of sorts. Whether the source contributes to crank failures would be hard to prove, but interesting none the less.
My initial thought is no as it seems to only be heard at idle (unless other sounds are drowning it out).
As the vote/pole is now, it's one and done. Is there a way to modify the voting to allow those unfortunate few who have broke more than one crankshaft to add that to the results?