<VV> Ok ... here it goes-

[Tony Underwood]

At 08:22 PM 8/23/2007, ScottyGrover at aol.com wrote:
>
>In a message dated 8/23/2007 7:44:51 P.M. Pacific Daylight Time,
>BobHelt at aol.com writes:
>
>A great  question, Cash. Bob Benzinger said that Chevrolet had to use the
>flexible flywheel because a solid caused a "freight train noise". This was
>true
>for the 140/144 cid engines BUT was it also true for the 164  cid engines?
>Chev
>never checked apparently. So maybe, just maybe, a solid  will work OK for the
>164  engine. Please let us know how it works  out.
>Regards,
>Bob Helt
>
>
>
>Years ago, I had a solid flywheel on my '66.  It was noisier than the
>riveted flywheel but it wore the clutch surface badly and I had to 
>remove it and
>put in a bolted flywheel.
>


Some years ago, I borrowed a stack of Corvair related magazines from 
a local club member.   Most dated back to the '70s, some even 
earlier.   There was a huge quantity of tech info in many of these 
publications that included engineering study as well as practical 
application results.   After I returned the magazines (following the 
guy ragging on me because someone else wanted to borrow them) I later 
returned to ask to "reborrow" them again and he said they were still 
"out".   Recently I chased the guy down and again asked about that 
stack of magazines and he said that they disappeared during a move 
several years ago, possibly thrown out by his wife who thought they 
were "just a box full of old magazines nobody was ever gonna look at 
again".    I was crestfallen...


In one magazine, there was an article I remember well in which this 
flywheel issue (among others) was discussed.   The author said that 
flywheels of the time when 'Vairs were being engineered, and even 
flywheels "today" (1970s), tended to be not as finely balanced as 
they should be, for use in a Corvair engine which has a "very short 
and light crankshaft" with small main and rod journals which allows 
flexing if a one-piece flywheel with anything less than perfect 
balance is used.   Radial vibration can be easily eliminated by 
drilling material from the"heavy side" of a solid flywheel so as to 
statically balance it to a fine degree.   However, this isn't enough 
when that flywheel gets bolted onto a Corvair crankshaft with its 
small journals, short length, and light weight crankcase which will 
allow dynamic imbalance to cause vibration to run rampant.

It's the same principle of balancing a tire by adding weights to one 
side of the wheel.  A bubble balancer shows the tire to be dead on, 
but put it on a spin balancer and it wobbles.  The bubble balance 
method shows static balance but spinning the tire demonstrates that 
other forces are at work.

The problems with solid flywheels is dynamic balance.  Add the clutch 
to this equation, combining it with the same static balance issues 
and things get complicated real quick.

The three piece flywheel with the outer cast portion and a steel 
"inertia ring" sandwiching a flex plate between them allows the 
rotating mass to wobble slightly to find its dynamic balance point 
without trying to bend the crankshaft in the process.  A good static 
balance of the stock flywheel gets pretty close, and the slight 
wobble via the steel flexplate takes care of the dynamic balance 
issues, thus the engine will spin relatively smoothly, even if the 
clutch itself isn't well balanced.   That flex plate solves several 
problems.

All in all, the factory flywheel is a remarkable piece of engineering.

It's not easy to dynamically balance a flywheel, although today's 
technology is up to the task, for a price.   There's not a real issue 
when a solid flywheel is mounted onto a crankshaft that's 2 feet long 
(or more) and weighs over 60 lbs and has mains that are 3 inches in 
diameter, parked in an iron crankcase weighing hundreds of pounds and 
surrounded by a very rigid bellhousing connected to a transmission 
with some serious mass as well.  Such a load of castings with a 
vibrating flywheel between them will dampen a lot of the buzz without 
a problem.   But a flywheel on a 'Vair crank that weighs only a 
little more than 20 lbs in an aluminum crankcase that weighs less 
than the crankshaft, with said flywheel running inside a bellhousing 
that is anything but rigid is gonna roar if the flywheel isn't 
*Perfect*, far as both static and dynamic balance goes.   And of 
course the clutch is a pot-luck toss-up.

A solid flywheel that vibrates and buzzes and roars also sounds 
(intentional pun) like a really good way to eventually crack a crankshaft.


I WISH those magazines were still around...  the flywheel situation 
explanation in that one particular magazine was the best one I'd 
heard, then or now.



tony..