Re: harmonic balancers, helpful?

Posted by Bob Carabbio on December 19, 1997 at 10:20:05

In Reply to: Re: harmonic balancers, helpful?
posted by Mike Flanagan on December 18, 1997 at 09:34:59

I'm going to see if I can find a large but amenable front balancer at a swap meet and stick it on just for comparison.The problem is that the small-block Chevy units weren't built very well to begin with, and tend to be EXPENSIVE - like $50-$75 at local swap meets since units that haven't delaminated their rubber are fairly rare.Without knowing the effect (if any) I'm not about to spring that kind of dough for a chunk of iron just to experiment with.
My business is related to the measurement of forces in Metalforming machine structures.one problem with that is that you tend to view metal structures as VERY dynamic objects consisting of masses connected by springs.In the "A" the crank is long and pretty spindly.The amount of torsional twist probably pretty considerable when #1 fires, and negligable when #4 goes. A Damper on the front of the shaft would absorb some of the torsional acceleration of #1 and #2 which would lessen the twisting effect on the crank, then give it back later in the stroke for a somewhat smoothing effect on the engine operation. At the very least it should make life easier on the crank.
Mike's point is well-taken, though.Since the flywheel is as big as a house (with an attached garage), it pretty much tries to make the shaft rotate at a constant angular velocity.However the bigger the flywheel, the more the firing impulses attempt to rotate the entire engine block which couples vibration right to the frame.My Father's Jordan Playboy had two flywheels - one at each end of the motor.
It's also true that you CAN'T perfectly balance a vertical 4-cylinder motor without additional equipment (like the silent shafts that everybody uses today) since there's a fairly strong vertical vibration that occurs at 2X crankshaft speed which is related to piston acceleration.The counter-rotating "Silent Shafts" are driven at 2X crank speed to take that out.
Certain autos have also used inertial absorbtion dampers to smooth them out - the Pinto is a good example with the big laminated chunk of iron that hung out behind the tranny.I'd like to pursue that also, but I'm not sure how to calculate the required mass/spring rate.At "A" frequencies, though it wouldn't be small.Be a wild conversation piece at a club meeting, though.
Bob Carabbio

Follow Ups:
thanks for the help ed Rohmer December 23, 1997 at 14:37:50(0)

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