This is, to me, a really good question. BMC engines - A series and
B-series - use balancers, while ford race engines do not (no idea about
street engines).
My understanding - feeble as it is with regard to this question - is that
the critical vibration frequencies vary with respect to stroke, so that the
long stroke BMC engines have a critical frequency right in the power band -
around 6,000 rpm??? and the shorter stroke Ford engines push that up to
about 6800 rpm in the case of the FFord. If so, that's one reason why
FFords aren't rev'd higher than 6800 rpm. Twin cams, BDA's etc, often are
setup to rev higher than this, since once past the critical frequency say
7,000 to 9,000 rpm, life should get better.
Other factors are crank stability - Fords have very good crankcases and
five stout main bearing caps, while BMC's are often three main bearings
(not later B-series). Vibration also tends to travel in the crank - Ford
based engines often have clutch and flywheel problems as a result of
vibration that BMC engines tend not to have. I've seen a number of FFord
engines with the flywheel bolts sheared off - even when using top quality
bolts correctly torqued. The BDA's use 12 flywheel bolts for this
reason. I've heard of clutch splines being damaged as a result of
vibration. There is some conversation in the FFord list about flywheel
weight having input to this, with a lower rotating mass relieving the problem.
I'd appreciate input from those who know more about this than I do...These
are my theories, not facts! :)
Brian
At 08:20 AM 02/14/2000 -0500, Joseph_Chimbolo@hyperion.com wrote:
>Here's a question someone may answer. I am restoring a FF. Why does a
>FF run
>without a harmonic balancer on the crank? I always heard that on V8's if it
>malfunctions the crank snout will snap off. So can I take off an MGB to save
>some weight?
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