Bill Babcock wrote:
> We're kind of saying the same thing--it's the usual problem of language
> imprecision.
>
> -----Original Message-----
> From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
> Of Randall Young
> Sent: Thursday, May 20, 2004 11:25 AM
> To: fot
> Subject: RE: cranks
>
>
>>Long stroke engines have high torque for an obvious reason--the length
>>of the lever arm (the distance of the rod centerline from the crank
>>centerline).
It's an interesting thread, at least in the sense that one is
dealing with what is pretty much a production crank--there can be
only incremental improvements to the original design, given the
package into which it must fit. After all, despite changes in
materials in aftermarket parts, the four-banger is still a
three-bearing crank, which means there's a goodly unsupported
distance, by design, between bearings. That encourages all sorts of
torsional loading and unloading in an inline-4, and that is the
origin of many vibrations. The inline-6 has the same problem, in
that it is a four-bearing crank, rather than seven-bearing. Lots of
room for it to twist and turn under load.
For those inclined to textbook explanations, I still recommend
Philip Smith's _The Design and Tuning of Competition Engines_ (5th
edition is probably the best of the bunch, if it can be found) for
explanations of the effects of crankshaft torsional wrapping and
unwrapping and how that encourages vibration. Good book. Serious
reading. Not for the timid. Interesting anecdote in the midst of the
subject about the BRM 16-cylinder H-configuration engine, and why
torsional loading was the undoing of that engine.
Cheers.
--
Michael D. Porter
Roswell, NM
Never let anyone drive you crazy when you know it's within walking
distance.
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