<VV> Harmonic Balancer / Solid Pulley on 140

[Ken Pepke]

The original question had to do with the advisability of the use of the solid pulley / inertia wheel / rear flywheel on a 110hp engine.  My response was to discourage that practice without getting overly involved in the engineering.  It is true that the better name, and more accurate reflection of its function, is torsional dampener.  Harmonic balancer is the more recognizable name.  Regardless of the name, the function remains the same.  And yes, like any and every rotating part, it should be balanced about its own center.  Although it does not apply to the Corvair engine, the exception is when the harmonic balancer does contribute to the balance of an engine.  In these cases it is most advisable to include them in the engine balance process.  For a Corvair they __are__ balanced by the manufacturer to a standard that is well suited to normal use so they are readily interchangeable as is.  Racers may wish to enhance this balance job.

It is also true that the firing of the pistons generates a torsional force that 'twists' the crankshaft within itself upon each firing of every cylinder after which the crankshaft, as it has not twisted far enough to reach the point of deformation,'unwinds' to its original shape.  Obviously this process happens many times in a minute for as many minutes as the engine is running.  Known by some of the 'old timers' as ringing, this process can approach, can equal, and can exceed the crankshaft's natural frequency as the engine speed / load varies.  This happens many times during an engine's lifetime.  Left unmanaged, this 'ringing' eventually may and sometimes does lead to catastrophic crankshaft failure leaving the driver on the side of the road and very disappointed.

But, let there be no mistake about it ... the condition referred to 'natural frequency' is HARMONIC!  

Ken P
Wyandotte, MI
Worry looks around; Sorry looks back, Faith looks up.

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> From: BobHelt at aol.com
> Date: June 12, 2011 11:45:33 PM EDT
> To: rsampson at kc.rr.com, hennerfeind_joe at yahoo.com, virtualvairs at corvair.org, kenpepke at juno.com, HallGrenn at aol.com, corvairduval at cox.net
> Subject: Re: <VV> Harmonic Balancer / Solid Pulley on 140
> 
>  
>  
> In a message dated 6/12/2011 9:00:33 A.M. US Mountain Standard Time, rsampson at kc.rr.com writes:
> I'd only use on an engine that's been balanced with the rest of the engine components
>  
> From what I have been reading here it would appear that nobody understands the function of an Harmonic Balancer. Probably that is because there are NO HARMONICS involved here and also that there is NO BALANCING going on with the harmonic balancer.
>  
> This device that mounts on the back end of the crankshaft and replaces the pulley really is a TORSIONAL DAMPER. It reacts to the twisting of the crankshaft caused by the piston impulses and dampens them. And when these impulses occur at the crankshaft's natural frequency they build up into a force that fractures the crankshaft. After many of these occurances the fractures grow to cracks and then breakage. By dampening these impulses the crankshaft is preserved.
>  
> Regards,
> Bob Helt




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