Balanced rotating assembly vs fluidampr

From everything I've seen and heard itll feel alot smoother idling and through rpm range. Sleeper status
 
I’m a mechanical engineer who balances motors — among other things — so perhaps I can shed some light on the subject.

First of all, it’s not a harmonic balancer; that is a misnomer. There is no such thing as a harmonic balancer; it is impossible to balance harmonic vibrations. Itis proper name is a harmonic damper; not dampener, not dampner, damper. Say it with me, DAMPER. Its purpose is to damp out or squelch torsional vibration. (A dampener is a wet cloth). :hehe:

That said, some harmonic dampers have an external weight attached to them; its function is to counter secondary impulses. (This type is called a combination harmonic damper/external balancer.) However, no straight 6 motors are externally balanced. This is because a 120° firing inline 6 naturally cancels both the primary & secondary impulses. All that is required is that the throws of the crank be equal in weight. In other words, one balances the crank at a 0% balance factor; no bobweight required.

To answer the OP question: Balancing a motor is ALWAYS a good idea. The motor will run smoother, make more power, & last longer. However, Cummins motors are balanced from the factory — quite well I might add — & unlike a V-8, which balances the crank based upon the rotating & reciprocating masses, once an inline 6 crank is balanced, it will never go out of balance unless weight is added or removed from the crank. All that is required is to ascertain the piston weights are all equal, as are the rotating & reciprocating ends of the rods.

Nervertheless, an inline 6 does have a lot of torsional vibration. That is why all straight 6 motors come with a damper from the factory. But the stock damper (which is nothing more than rubber of a particular density sandwiched between two steel rings) works by turning the vibration into heat; thus destroying itself in the process. Also, rubber dampers work within a narrow range of frequencies, so the factory picks the vibration with the largest amplitude, uses a rubber density that will absorb that, leaving the rest of the frequencies undamped. A Fluidampr uses a metal ring running in viscous silicone to squelch ALL frequencies, thus making them much more efficient.

So, to recap: balance your motor & run a Fluidampr; you’ll be glad you did.
 
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this is NOT the sort of thread that leads itself to sensibility. First post fail.


LOL j/k Good post.
 
I agree, great post.

I admit, I used the term balancer. I did so because many times over it is easier to talk to a person in their terms. They may not be correct, but the person follows your train of thought. I in no way meant that a damper can act as a dynamic force to balance an engine, simply stating in some engines it's part of a balanced assembly.

Cut7, I've read about instances of rapid engine rpm change and fluidampr's having problems. I don't imagine this is a problem with the <6000 rpm our engines see, but what are your thoughts?
 
So its not used to try and balance the torsional forces of each of the 6 different cylinders to then even out each one to make the vibrational shock of each one less noticed. No no way it should be called a balancer or damper maybe just space ship
 
TheBigNasty said:
Cut7, I've read about instances of rapid engine rpm change and fluidampr's having problems. I don't imagine this is a problem with the <6000 rpm our engines see, but what are your thoughts?
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It's not so much the rpm the engine turns, but the change in rpm; i.e., how fast the motor accelerates. Certainly not a factor with our 56 Kg (124 lbs.) cranks.
 
turninheadz94 said:
So its not used to try and balance the torsional forces of each of the 6 different cylinders to then even out each one to make the vibrational shock of each one less noticed. No no way it should be called a balancer or damper maybe just space ship
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Not sure if this is a serious inquiry, or you’re just being sarcastic. But in the case of the former, I respond: No, it doesn't balance, it absorbs the torsional springing (winding & unwinding) of the crank. In the case of the latter, please refrain from replying to all my future posts. I'm just trying to be helpful, & I'm sure someone here finds my posts useful.
 
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cut7 said:
It's not so much the rpm the engine turns, but the change in rpm; i.e., how fast the motor accelerates. Certainly not a factor with our 56 Kg (124 lbs.) cranks.
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I was thinking more along the lines of rapid deceleration. These transmissions are getting stronger and stronger, and the shifting can be made quite harsh.

Also, would you not agree that an equal weight and dimension item spinning at 10,000 rpm would have more inertia than one spinning at 3,000 rpm?
 
TheBigNasty said:
I was thinking more along the lines of rapid deceleration. These transmissions are getting stronger and stronger, and the shifting can be made quite harsh.

Also, would you not agree that an equal weight and dimension item spinning at 10,000 rpm would have more inertia than one spinning at 3,000 rpm?
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I do agree most emphatically. And it's not a linear increase, but rather, an exponential one. That being said, even if the shift is very firm, the Δrpm on a truck is only ~1250 max.
 
cut7 said:
I’m a mechanical engineer who balances motors — among other things — so perhaps I can shed some light on the subject.

First of all, it’s not a harmonic balancer; that is a misnomer. There is no such thing as a harmonic balancer; it is impossible to balance harmonic vibrations. Itis proper name is a harmonic damper; not dampener, not dampner, damper. Say it with me, DAMPER. Its purpose is to damp out or squelch torsional vibration. (A dampener is a wet cloth). :hehe:

That said, some harmonic dampers have an external weight attached to them; its function is to counter secondary impulses. (This type is called a combination harmonic damper/external balancer.) However, no straight 6 motors are externally balanced. This is because a 120° firing inline 6 naturally cancels both the primary & secondary impulses. All that is required is that the throws of the crank be equal in weight. In other words, one balances the crank at a 0% balance factor; no bobweight required.

To answer the OP question: Balancing a motor is ALWAYS a good idea. The motor will run smoother, make more power, & last longer. However, Cummins motors are balanced from the factory — quite well I might add — & unlike a V-8, which balances the crank based upon the rotating & reciprocating masses, once an inline 6 crank is balanced, it will never go out of balance unless weight is added or removed from the crank. All that is required is to ascertain the piston weights are all equal, as are the rotating & reciprocating ends of the rods.
Nervertheless, an inline 6 does have a lot of torsional vibration. That is why all straight 6 motors come with a damper from the factory. But the stock damper (which is nothing more than rubber of a particular density sandwiched between two steel rings) works by turning the vibration into heat; thus destroying itself in the process. Also, rubber dampers work within a narrow range of frequencies, so the factory picks the vibration with the largest amplitude, uses a rubber density that will absorb that, leaving the rest of the frequencies undamped. A Fluidampr uses a metal ring running in viscous silicone to squelch ALL frequencies, thus making them much more efficient.

So, to recap: balance your motor & run a Fluidampr; you’ll be glad you did.
Click to expand...

So if I have a balanced cummins crank, I upgrade rods and pistons (heavier), balance the rods and pistons, my crank does not need to re-balanced?
 
cut7 said:
I’m a mechanical engineer who balances motors — among other things — so perhaps I can shed some light on the subject.

First of all, it’s not a harmonic balancer; that is a misnomer. There is no such thing as a harmonic balancer; it is impossible to balance harmonic vibrations. Itis proper name is a harmonic damper; not dampener, not dampner, damper. Say it with me, DAMPER. Its purpose is to damp out or squelch torsional vibration. (A dampener is a wet cloth). :hehe:

That said, some harmonic dampers have an external weight attached to them; its function is to counter secondary impulses. (This type is called a combination harmonic damper/external balancer.) However, no straight 6 motors are externally balanced. This is because a 120° firing inline 6 naturally cancels both the primary & secondary impulses. All that is required is that the throws of the crank be equal in weight. In other words, one balances the crank at a 0% balance factor; no bobweight required.

To answer the OP question: Balancing a motor is ALWAYS a good idea. The motor will run smoother, make more power, & last longer. However, Cummins motors are balanced from the factory — quite well I might add — & unlike a V-8, which balances the crank based upon the rotating & reciprocating masses, once an inline 6 crank is balanced, it will never go out of balance unless weight is added or removed from the crank. All that is required is to ascertain the piston weights are all equal, as are the rotating & reciprocating ends of the rods.

Nervertheless, an inline 6 does have a lot of torsional vibration. That is why all straight 6 motors come with a damper from the factory. But the stock damper (which is nothing more than rubber of a particular density sandwiched between two steel rings) works by turning the vibration into heat; thus destroying itself in the process. Also, rubber dampers work within a narrow range of frequencies, so the factory picks the vibration with the largest amplitude, uses a rubber density that will absorb that, leaving the rest of the frequencies undamped. A Fluidampr uses a metal ring running in viscous silicone to squelch ALL frequencies, thus making them much more efficient.

So, to recap: balance your motor & run a Fluidampr; you’ll be glad you did.
Click to expand...

Good info right there... I too am a Mechanical Engineer, i thoroughly enjoyed reading this...
 
DPC said:
So if I have a balanced cummins crank, I upgrade rods and pistons (heavier), balance the rods and pistons, my crank does not need to re-balanced?
Click to expand...

As long as all the piston weights are equal, you'll be fine. Also, if you're going to install different rods, the rotating & reciprocating ends must all be equal. This only applies to an I-6 or a 60° V-12, not V-8s or I-4s.
 
This is terrific info..

I am freaked out that there's explosions in my engine thou.
 
DPC said:
So if I have a balanced cummins crank, I upgrade rods and pistons (heavier), balance the rods and pistons, my crank does not need to re-balanced?
Click to expand...

Going to go out on a limb and say when you add that weight to it that it wouldn't be a bad idea to have it rebalanced
 
Mine was balanced with complete rotating assembly. Including fluidmpr,pistons, rings, wrist pin with clips, rods, bearings crank. fwiw

from phone
 
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