Allen Nugent wrote:
>
> At 22:07 6/05/98 -0400, you wrote:
>
> >Inline 6's seem to last longer than V8's or V6's.... An old timer mechanic
> once
> >explained to me that it's because the crank is being loaded from one
> direction >only, as opposed to a "V" where it's being loaded side to side as
> well... Sounded >good to me.
>
> I've only read one book on engine design (which included software for
> modelling your own designs), and according to it, that's rubbish.
In the simplest terms, you're absolutely right, Allen. BTW, what's the
modelling software you mention? Widely available?
> People
> without training in mechanical engineering, or a lot of practical
> experience, always tend to think in static, rather than dynamic terms. In
> fact, the V8 is the smallest engine configuration that is capable of being
> perfectly balanced, both statically _and_ dynamically. Therefore, the
> bearing forces should be less than in a 6. Just another example of why you
> can't always depend on intuition.
Bearing forces are another nebulous area, but can generally be thought
of as a balance between sufficient bearing area without making the crank
longer between supports. From one standpoint, the V8 has a quite short
crankshaft for the number of cylinders, and therefore will have less
beam deflection and presumably less weight--although, the 45 deg. V8
crank does require considerable counterweighting. Weight is part of the
reason why the Cosworth V8s had single-plane crankshafts (which induces
another problem, that of low-speed vibration from rocking couples, which
isn't a real problem at very high rpm, but would be quite noticeable in
a passenger car).
> As to why 6's last longer - do they really? If so, I don't know why.
This is probably one of those Fords are better, Chevies are better, sort
of debates. There have been some truly atrocious V8s and exceptional
inline-6s, but that hardly proves a point, as you suggest. What likely
matters more is the attention given to the individual design. Regardless
of type, the block with the greatest stiffness and main bearing support,
the crank with the least torsional and beam deflection, the engine with
the best materials and the best vibration control is going to prove
itself over time.
Cheers.
--
My other Triumph runs, but....
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