Harmonic Dampener

[EngineTech1]

Wanted to hear some people's thoughts on what are considered to be the best dampers out there and why. I have my own opinions on this as well as alot of other things of course, just looking for some input.

[bill jones]

-while we at it if anybody has specific results with 4 cylinder engines I'd appreciate some info about the 4 bangers.

[whitevette]

What does a harmonic dampener do? It "damps out" the vibrational whipping of the rotating mass (known as ... in this case... the crank/rods/pistons/rings/etc. ). That's the theory, anyway.

[ChadS]

We predominately use ATI's and find they have performed the best so far for us.


Chad

[Guest]

I think there's big money in convincing us all that there's terrible torsional vibration associated with a running crankshaft. You know, "if you don't put a stop to it, cranks will break, valvetrains will suffer a whole host of problems, bearings will be shot, and horsepower will go down the tubes". Maybe this is true, maybe it's not, or maybe the truth is somewhere inbetween. I do know there are plenty of very high-end racing engines running around with no vibrational dampener at all and I just haven't seen the negative effects that have been claimed.

Take a 410 sprint car motor for example. They make about 850 hp in a harsh endurance racing scenario, they have a relatively long stroke and light weight crank (both factors that should theoretically increase problems with torsional vibration) and what do they run for a crankshaft dampener? Nothing! They don't use one! To make matters worse, they use a gear drive or a timing chain rather than a belt drive. These motors should be suffering the most from torsional vibration, but they don't have crank, bearing, or valvetrain problems even though they don't run a crank dampener. Now, they do drive a mechanical water pump off the front of the crank though. Perhaps that acts somewhat like a dapener, but I don't know.

I'd like to hear real world results fron dyno testing with and without a crankshaft dampener. Does anyone have any?

[John Haskell]

I have witnessed cast iron crankshaft failiar, main bearing issues, main bulkhead failiar in the days of old, prior to any aftermarket dampers. When I met Don Nicolson in the early days of Pro Stock Drag racing, he had the same issues untill he bought a 'Fisher' damper, which had just gotten into the business. I bought one and his damper greatly reduced the problems. The engine had a completely differant sound, greatly reducing the exhaust note and took the throttle quite differantly. It was the single most unusual thing I've noted by changing one part. It really convinced me early on, that block mass & crankshaft material was of the utmost importance. This damper was a crutch, but it talked enough to you about what is going on. ------- It may be the 410's are getting away with nothing up front due to the good parts that we have today. But if the parts are marginal, I question this would be positive w/o out some form of damping device.
One other item of interest is, I have noted the longer the snout, the more the potential problems. I wittnessed twice, snouts with the dampers attached, slung right off the engines. -------- I believe Fisher has dampers for Harleys, so I would think they would have them for 4's as well. They at one time, had springs and friction rings whitch were adjustable in tension @ regulating the force of damping although I'm not positive of what they use today.

[Racer Roy]

If I can add two cents about the sprinter engines...
In addition to not having a damper, they also do not have a flywheel or torque converter on the back end of the crank.
I would think that this would lessen the potential for torsional motion within the crank.

RR

[EngineTech1]

I thought I saw somewhere once where some cranks built specifically for sprint car apps. had some form of damping built into the counterweights. Not sure if this had something to do with the material used for balancing or whatever or if it was a specific design and construction difference but this was the impression I got. I have pretty much only seen ATI's on all the really high end endurance and drag race engines I've been around like the cup and busch engines and some really nice drag engines. I wonder if Darrin could say what type of Damper R&M uses on their pro stock engines as well as their super series engines.

[Guest]

Lunati markets a crank with special counterweights meant to deal with applications with no damper, but they're not even in the ball park of what a competitive 410 sprint motor would have in it. A good 410 has a very light weight billet 3.800 stroke with nothing special related to running in the absence of a dampener.

[Ken_Parkman]

This is a topic I have been researching lately. I have the advantage of working at a place where one of the foremost experts on engine dynamics is - unfortunately it's aircraft turbine engines. But we talked about theory as applied to a piston engine. I can hopefully add some info as to the theory of all this, I'm wondering if there is some experience that backs up the theory.

The problem is every component no matter what it is has natural frequencies built into it, and if there is an exciting force at one of these frequencies this can be disasterous. This industry has taught me tremendous respect for vibration. So as applied to a crankshaft here goes: The crank assembly has a frequency at which it wants to torsionally vibrate. When the engine is operated at a speed where the frequency of the cylinders firing (exciting force) corresponds to the crankshaft assembly natural frequency the crank can go into a torsional vibration, and if the rpm dwells at this point long enough bad things start to happen. My experience has been the first sign of this is timing chain stretch, progressing on to cracked cranks, then to complete failure. My opinion is if (big if) you have excitation of a natural frequency the HCF stress generated can be astronomical. I can back this up a bit with some strain gage work we were doing chasing an engine casing failure. This was on a nickel superalloy case that was cracking in an area that technically had no load. Once we found the exciting frequencey we found vibratory stress that defied belief. This superalloy that was not carrying any load would only last seconds when we ran the engine at the exact right speed.

The natural frequency is a function of crankshaft assembly polar moment of inertia and stiffness, the stiffer the crank the higher the frequency, the heavier the component in the assembly, especially the flywheel, the lower the frequency. Dampers are either amplitude or frequency sensitive (the pendulum style has been used in aircraft piston engines and does work, I have not figured out how yet) I have always liked the amplitude sensitive style like the Fisher as it is independant of the frequency, but due to other reasons I will no longer deal with them. The frequncy sensitive design is theoretically more ideal if tuned correctly, but this is my problem - how do you tune it? I know eqipment exists to do this, but it is way beyond my resources. Do the high end Nascar guys do this tuning with the ATI? And I would think if you changed the flyweel for example this style damper would need to change.

I'm wondering if this is how the sprint car guys can survive with no damper at all. Maybe the light crank and especially the no flywheel pushes the frequency above the point where the engine rpm can reach, therefore there is no exciting force, therefore no need for a damper at all. My dynamics buddy (who knows nothing about piston engines) figures from our conversation that the flywheel is the most important of the assembly from a frequency point of view cause of it's large diameter. Has anyone ever looked into stuff like this?[/i]

[GUEST]

I WAS WONDERING IF RUNNING THE WATER PUMP FROM THE CAM AND OIL PUMP AND STEERING PUMP FROM THE BACK OF THE CAM WOULD DAMPEN THE HARMONICS IN SOME WAY, WOULD THE FLUID IN THESE PUMPS ACT AS A DAMPNER IN SOME WAY ?

[Wolfplace]

man"]This is a topic I have been researching lately. I have the advantage of working at a place where one of the foremost experts on engine dynamics is - unfortunately it's aircraft turbine engines. But we talked about theory as applied to a piston engine. I can hopefully add some info as to the theory of all this, I'm wondering if there is some experience that backs up the theory.

The problem is every component no matter what it is has natural frequencies built into it, and if there is an exciting force at one of these frequencies this can be disasterous. This industry has taught me tremendous respect for vibration. So as applied to a crankshaft here goes: The crank assembly has a frequency at which it wants to torsionally vibrate. When the engine is operated at a speed where the frequency of the cylinders firing (exciting force) corresponds to the crankshaft assembly natural frequency the crank can go into a torsional vibration, and if the rpm dwells at this point long enough bad things start to happen. My experience has been the first sign of this is timing chain stretch, progressing on to cracked cranks, then to complete failure. My opinion is if (big if) you have excitation of a natural frequency the HCF stress generated can be astronomical. I can back this up a bit with some strain gage work we were doing chasing an engine casing failure. This was on a nickel superalloy case that was cracking in an area that technically had no load. Once we found the exciting frequencey we found vibratory stress that defied belief. This superalloy that was not carrying any load would only last seconds when we ran the engine at the exact right speed.

The natural frequency is a function of crankshaft assembly polar moment of inertia and stiffness, the stiffer the crank the higher the frequency, the heavier the component in the assembly, especially the flywheel, the lower the frequency. Dampers are either amplitude or frequency sensitive (the pendulum style has been used in aircraft piston engines and does work, I have not figured out how yet) I have always liked the amplitude sensitive style like the Fisher as it is independant of the frequency, but due to other reasons I will no longer deal with them. The frequncy sensitive design is theoretically more ideal if tuned correctly, but this is my problem - how do you tune it? I know eqipment exists to do this, but it is way beyond my resources. Do the high end Nascar guys do this tuning with the ATI? And I would think if you changed the flyweel for example this style damper would need to change.

I'm wondering if this is how the sprint car guys can survive with no damper at all. Maybe the light crank and especially the no flywheel pushes the frequency above the point where the engine rpm can reach, therefore there is no exciting force, therefore no need for a damper at all. My dynamics buddy (who knows nothing about piston engines) figures from our conversation that the flywheel is the most important of the assembly from a frequency point of view cause of it's large diameter. Has anyone ever looked into stuff like this?[/i]

=
First, let me say I use ATI almost exclusively & have been extremely happy with them.
You asked if the cup guys do any testing. Yes they do & a gentleman named JC Beattie Jr spends a lot of time tuning dampers for different applications & combos & has a pretty in depth understanding of dampers,,
I will ask him if he has the time to stop in with his own opinions & observations on this forum

[putztastics]

Ken, would you say torsional vibration could be called twisting vibration - is it different from vibration aggravated by a running frequency or running harmonics? It really can’t be balanced in the same sense as balancing an engine’s rotating assembly can it?

Vibration aggravated by running frequency or harmonics is called "critical vibration" in the steam turbine/generator industry. The RPM ranges at which this happens are called "critical vibration RPMs" and yes you don't let the machine sit there but run it right through to a safe RPM. I have never heard of running piston engines being tested for critical vibration RPM ranges but do plan to test a restricted circle track engine this way soon. I too would guess there are piston engine failures attributable to running in a critical RPM range without even knowing it was happening. Balancing on a steam turbine/generator is done way different than a piston engine. They are balanced for a specific RPM (usually 3600) and the balance is checked while running at that RPM. They are balanced in between each set of bearings using vibration pickups on each bearing. The vibration and RPM is recorded on a strip chart showing the vibration from 0 RPM to 3600, this is how the critical vibration RPM ranges can be mapped. My plan for the restricted engine is to run a vibration test this same way during a dyno sweep test.

Most V-8 cranks don't even have the center counterweights to allow balancing between all main bearings. A V-8s crankshaft/cylinder block is so strong internal imbalance (between main bearings) is routinely corrected with external balance on the flywheel or vibration damper. I don't think steam turbines are ever externally balanced.

[Ken_Parkman]

That's the way I understand it, it is a twisting vibration, and yep, it really can't be balanced in a standard sense. In this case it's really not related to balance at all. And I would agree with the term critical vibration. But as this is a torsional vibration I'm not even sure you could pick it up with an overall engine vibration. Probably the factories (and maybe ATI?) have chased this all around and could answer. And I am absolutely convinced there have been critical vibration failures (one of my cranks) in piston engines. At this point after seeing some amazing frequency related stuff in turbines I am convinced a big percentage of all failures are caused by this, especially in valvetrains.

On the high speed engines the effort into balancing is amazing. They can't balance at engine operating speed (up to 56,000 rpm) so everything is balanced at every concievable level. Parts are runnout anaylzed and stacked so that the mass centerline is as perfect a line as possible, and major effort is made to ensure the parts are as perfect as possible, minimum balancing actually needed. There is a whole science (black art) to it. The vibration readings the same way, two pickups and a vibration survey throughout the entire operating range. But then they break the readings down into frequency components and show this on a 3-d plot. They can pick up for example a starter vibration this way. My dynamics buddy can literally explode your head with the complication of this stuff.

It's too bad he doesn't know what a piston engine even looks like, but I am going to try to pick his brains a little more. When I did mention external balance he could not believe it existed and started talking about rotating moments. However the speed ranges are a little different so it's not quite the same thing in a piston engine. I'll ask him what he thinks about pumps and things as dampers, but I don't think a pump would be effective.

[Ken_Parkman]

Just found some great related info:
http://www.eng-tips.com/viewthread.cfm? ... 602&page=4