Re: Balance and manners

[bearbvd@domain.elided (Greg Hermann)]

>In V7 #628, Greg Hermann said:
>
>"This strikes me as unadulterated and totally
>unnecessary B.S.!!! Did they recommend checking the
>sponson rods and grease the muffler bearings regularly
>too?? Or were those not profit center operations for
>their shop??
>For starts--the cams turn at 1/2 engine speed, to
>continue, there isn't a part of the cams far enough
>from their centerline to generate any really
>significant imbalance force!!"
>
>1. This is almost unforgiveably rude. I was not
>brought up to speak thus to my elders, nor to anyone
>else in the course of a polite discussion...which is,
>after all, what the Digest is supposed to be.
>
>2. Getting down to the actual meat of the matter: If
>you're REALLY going to balance an engine, you can't
>dismiss ANY significant rotating or reciprocating
>mass, can you? And "half-speed" at 7500 rpm is still
>3750, which ain't exactly poking along.
>
>Back when I was still a naive neophyte, up in
>Anchorage AK the hot tip was to bundle up every single
>moving part of your engine and send it down to this
>aircraft-engine facility in Seattle for the full
>static-and-dynamic balancing treatment. I know it
>worked, 'cause one guy had a fully-balanced 850 Mini
>that ate Coopers for brunch, at least until the 1275s
>came along...

Will--

You may or may not be my elder--but the demographics of the list are such
that  the probabliity that you are is not very great!--But--anyway---

Scuze me if you thought it was rude of me to convey my opinion and feelings
in that manner. It was an attempt at humor, in an attempt to help others,
who might be tempted to WASTE their money in the pursuit of balanced
camshafts, and convey to any who wished to listen that there might be FAR
more productive ways to spend what money they have available on things
capable of making a race car faster and more reliable! Since you did not
like it that way, let me state it more specifically!!---Here ya go----

I first heard about the "balancing the cams and sprockets" routine, I think
in '71 when racing an Alfa. It struck me (and some  other well qualified
engineers as well) as kind of comical overkill at that time--and after
another 28 years of professional engineering practice, it appears even more
hilarious (at least to me) as a deja vu! The action of the parts in the
valve train is unbalanced to begin with (valves, springs, retainers,
keepers, tappets, etc.) to a FAR greater degree than the cams or sprockets
ever could possibly be, and this has no ill effects in terms of shaking the
engine!

Let us not forget that the force generated by an unbalanced, rotating part
varies with the SQUARE of its rpm, so 3750 cam rpm grows quite a bit less
significant than you imply it might be in terms of any shaking couples
which an unbalanced cam might generate!

Not to mention that any unbalance forces generated also vary with the
SQUARE of the distance of the unbalanced mass from the centerline of the
rotating part!  The cams, and not even their drive sprockets, are simply
not of large enough diameter to generate particularly large unbalance
forces, and the idea that any such forces which do exist could be large
enough to amount to a significant percentage of the loadings on the cam
bearings from the drive chain and the valve inertial forces and valve
spring forces is simply ludicrous!

And excessive bearing loadings and engine vibration are what careful
balancing is all about!!

And my considered professional opinion is that if anyone receives a
suggestion that balancing the camshafts in a race engine would be
productive in terms of engine smoothness or reliability, that the suggestee
should take a hard look at the economic motivations and/or the technical
qualifications of the suggester!!

And, TRUST ME, this is NOT a flame!

Regards, Greg (licensed P.E. in two states (in the USA), & an engineering
degree in machine design, from Cornell Univ.)

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End of alfa-digest V7 #629
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