Destroying the dogma: lightweight crankpulleys

[RL7]

I figured the effect of the belts would be negligible, was just wondering. I'm thinking if you go back to the guitar analogy, it would be like putting a piece of paper on the strings rather than a towel. Just out of curiosity- is there ANY modern engine that comes from the factory without some sort of harmonic balancer?

[Hard AttacK]

Fuuuuuuuuuuuuuuuuuuuu

[Trab]

O well i got me a stocker coming YAH

[J. Fast]

Very interesting article. I would have to question wether problems with dampener failures are also stemming from an out of balance counterweight on the other end of the crankshaft, the flywheel. My interpretation of the article is the the harmonic resonance thru the crankshaft can be reduced if you have a properly weighted and balanced flywheel. So what happens if the flywheel is cut and not properly balanced or you install a clutch that slowly strips away flywheel material causing an uneven wear pattern on the flywheel?

The second thing I also noticed is the crankthrow points of defection are also suspect as they have seperate modulus if different friction producing materials are utilized at each pivot point and each adjoining point. When engines get old they shed bearing and ring material aswell and if the material being utilized is not uniform it's possible to also increase the resonance. Page 22 illustrates the stress analysis on the crankthrow pivoting locations. Depending on the frictional coefficients and usable life of the material the harmonics in an engine can also change the deflection rate which affects balance.

If you're flywheel is weighted and balanced properly, your engine is properly balanced and has clamping surfaces with the same modulus, and you're within radial and lateral runout specs I would disagree that a harmonic balancer is necessary. If all moving parts are held to tight to weight and balance specifications and you prevent vibration stackup a solid is probably fine.

30K miles with around 700 ft/lb at the crankshaft on an Unorthodox and no harmonic problemos here.

One other thing I noticed in the article was resonance and harmonic waves on the drivetrain. Kinda had me thinking about problems with exploding drivetrain parts. The lower the harmonic resonance in a tortional rotating assembly, the less damage you cause.


Really cool article Pete,

Jeremy

[i3igpete]

Very interesting article. I would have to question wether problems with dampener failures are also stemming from an out of balance counterweight on the other end of the crankshaft, the flywheel. My interpretation of the article is the the harmonic resonance thru the crankshaft can be reduced if you have a properly weighted and balanced flywheel. So what happens if the flywheel is cut and not properly balanced or you install a clutch that slowly strips away flywheel material causing an uneven wear pattern on the flywheel?

The second thing I also noticed is the crankthrow points of defection are also suspect as they have seperate modulus if different friction producing materials are utilized at each pivot point and each adjoining point. When engines get old they shed bearing and ring material aswell and if the material being utilized is not uniform it's possible to also increase the resonance. Page 22 illustrates the stress analysis on the crankthrow pivoting locations. Depending on the frictional coefficients and usable life of the material the harmonics in an engine can also change the deflection rate which affects balance.

If you're flywheel is weighted and balanced properly, your engine is properly balanced and has clamping surfaces with the same modulus, and you're within radial and lateral runout specs I would disagree that a harmonic balancer is necessary. If all moving parts are held to tight to weight and balance specifications and you prevent vibration stackup a solid is probably fine.

what you have to remember is that once the clutch is engaged any balance issues from the flywheel disappear, since you are also now supported by the transmission bearings. similarly, recall that lateral runout causes euler bending forces and radial runout causes centrifugal forces - not the same as torsional. excessive runout in an engine with a torsional damper will still grenade.

you are correct that as bearings age, they affect friction. in industry this is modelled as absolute damping - think of it as a damping term applied to the journal that is a function of engine speed. however, the mechanics of how the crank damper is tuned does not change. recall that any forces on a frequency domain system are called forcing functions - they don't change the system itself, but rather the right hand side of the ODE*. that means that the tuning of the damper does not change with age of the bearings/friction.


*ordinary differential equation:

[J. Fast]

you are correct that as bearings age, they affect friction. in industry this is modelled as absolute damping - think of it as a damping term applied to the journal that is a function of engine speed. however, the mechanics of how the crank damper is tuned does not change. recall that any forces on a frequency domain system are called forcing functions - they don't change the system itself, but rather the right hand side of the ODE*. that means that the tuning of the damper does not change with age of the bearings/friction.

I understand the tuning of the dampener will not change. However if your engine is designed with low resonant frequencies and the vibration ampitudes are low then there is no reason for dampening it.

Another example the article never really addressed is over-tuning and under-tuning a dampener which has to do with shifting the amplitude vs. frequency curve position in the rpm range (page 40). You can add weight or take it away from the balancer and can shift the peak amplitude vs. frequency position to an area that a vehicle will rarely operate in.

Jeremy

[i3igpete]

actually, what is more common for motorsport applications where no crank damper is used is to stiffen the crankshaft as high as possible. this increases the natural frequency sufficiently high that the max rpm (and thus firing frequency) aren't high enough to excite it. for example, the sports prototype crank i'm working on right now has severely underbalanced counterweights. This reduces the inertia, and thus increases the first natural frequency.

they have sacrificed in-throw balance in order to not need a crank damper. i should mention here that in-throw balance is not the same as the summed balance - summed balance is what you feel and remains the same because it only depends on engine configuration.. in throw balance is the balance between two given journals.

[UTRacerX9]

30K miles with around 700 ft/lb at the crankshaft on an Unorthodox and no harmonic problemos here.

Jeremy

I've got nearly 50k miles on my engine using lightweight flywheels and crank pulleys... no problems. I had an Unorthodox on there for 40k of it, but I got tired of my headlights flickering when at idle sometimes, so I put a 3SX stock sized one on about 10k ago. I've had a UR flywheel for that same time period also.

Honestly, I still can't believe people argue about this, it comes down to personal preference. I prefer having a lighter rotating assembly, and sticking with a td04 based turbo, running a max of 18-19 psi. Far more people have blown up their engines due to overboost conditions than have ever screwed up an engine due to ditching the harmonic balancer.

[92RT-TT]

After the things I've read I dont think I'd ever put a lightweight crank pulley on.

[Vince86]

I've got nearly 50k miles on my engine using lightweight flywheels and crank pulleys... no problems. I had an Unorthodox on there for 40k of it, but I got tired of my headlights flickering when at idle sometimes, so I put a 3SX stock sized one on about 10k ago. I've had a UR flywheel for that same time period also.

Honestly, I still can't believe people argue about this, it comes down to personal preference. I prefer having a lighter rotating assembly, and sticking with a td04 based turbo, running a max of 18-19 psi. Far more people have blown up their engines due to overboost conditions than have ever screwed up an engine due to ditching the harmonic balancer.

Amen.