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Re: torsional damper and how they work
...decent article on how torsional vibration dampers work, but it has the typical incorrect terminology. Dampers do not provide "dampening". It's DAMPING!
At least he called the device a "damper", not a "dampner".
A crankshaft can get into trouble if the RPM approaches the natural torsional vibration frequency of the crankshaft. The complex geometry of crankshafts make them very difficult to anlayze, especially back in the pre-computer days.
Broken cranshafts led to experiments on torsional vibration using strobe lights to observe deflection, and then dampers were fabricated and tested until the observed deflections were minimized. Since damping is only required in a range near the natural torsional frequency of the crankshaft, conventional friction type dampers work very well as long as they are properly tuned.
A good understanding of the phenomenon was gained during WW II since it was a particulary vexing problem on aircraft engines due to the propellor being effectively a part of the crankshaft, and like so much other technology that was developed during WW II, it migrated to the auto industry in the early post war years.
The term "harmonic balancer" somehow came into being because the torsional damper mitigates resonant crankshaft torsional vibration, both first mode and sometimes the higher order harmonics, but it's really a misnomer. It's a damping device, not a "balancer".
I always call them what they are - torsional (vibration) dampers.
The engine has a second torsional damper on the back end - the damper in the clutch hub. This effectively decouples the engine harmonics from drivetrain harmonics. The torque converter performs this function with automatic transmissions.
Duke -
Re: torsional damper and how they work
In the instance of the older small blocks that do not use a threaded crank snout what would be the preferred method of damper installation. I have one of the Kent-Moore pushers but without a hole to screw it into there is no way to use it. The balancer on my engine shows evidence of hammering, apparently before the invention of compothane dead blow hammers!
Don yesacavageComment
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Re: torsional damper and how they work
I can't help you on that one, but I'm sure others can.
The only torsional dampers I've removed or installed were the 8" type for SHP cranks that have the treaded center hole, and they are easy.
DukeComment
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Thanks Duke...
I feel better now that someone finally has used the term damper instead of dampener. Same goes with Midyear suspension "trailing arms". That term means nothing to me. The Assembly Instruction Manual refers to them as "torque arms" and everyone tells me...WTF are you talking about? PTComment
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Re: Thanks Duke...
I'm guilty of using "trailing arm". Some GM parts nomenclature is esoteric, but I try to use their termminology. "Torque arm" is also functionally correct because this particular piece of the suspension tranmits wheel drive and brake torque to the chassis. It also transmits linear longitudinal forces to the chassis while the "drive shaft" (half-shaft) and "strut" (strut rod) transmit lateral forces.
The term "damper" is a generic term using in the engineering community (mechanical, electrical, whatever...) to describe a device that provides "damping", not a "dampner that provide "dampning" or a "dampener" that provides "dampening".
I can usually get a read on one's technical background from the terminology they use.
DukeComment
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Re: torsional damper and how they work
In early 1969 I wanted to rebuild my 64 327/300 Corvette because it would produce just a little bit of smoke when I really got on it. Only about 60k on the odometer. Had it balanced and I installed a new mild Crower cam, not solid lifter, and new damper. I had to force the damper on, did some slight damage to it. Ran really great, with 4-speed and 3:08 it would run up some speed in first gear. The damper came off and strapped for time I took it to the local Chev dealership on Coronado and another new one was put on. Still have the indented almost new damper. Have always wondered what the machine shop sold me.Comment
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Re: Thanks Duke...
I don't believe the C2/C3 trailing arms transmit any drive torque to the chassis; the drive torque reaction point back to the chassis is the differential housing, through the diff nose mounting bracket and the diff mounting crossmember. In terms of drive torque, all the trailing arms provide is a bearing for spindle rotation, and they impart a forward force vector to the chassis through the front bushing through-bolt under acceleration.Comment
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Freebody diagram enclosed
It's been a while since I did one of these, but if we isolate the rear suspension in a freebody diagram, there is a thrust force at the tire contact patch, which is resisted by and equal force reaction at the trailing arm pivot, but since these forces are not inline they create a moment.
This moment is resisted by a vertical force reaction at the trailing arm pivot and an opposite force exerted by the spring, so the trailing arm is loaded in both compression (under acceleration) and bending.
The above reactions clearly result in additional squat under acceleration that adds to squat caused by the overall clockwise moment of the drive thrust times its moment arm from the cg. Two trailing arm designs, one above the other, like on C4s and later generations reduce the effective moment arm from the cg, so they squat less under acceleration.
I can't find any reference to "torque arm" in my '63 AIM since the entire assembly including the brakes were shipped to the plant and are referred to as "spindle support arm and brake assembly", but the P&A catalog noun for the individual part is "ARM, torque control".
DukeComment
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Re: Freebody diagram enclosed
Duke -
I agree with the force vectors and the moment they create under acceleration from not being in-line, but (simplistically) all the trailing arm is is a pillow block for a rotating shaft; it doesn't transmit any "torque" reaction through its attachment to the frame.Comment
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