Big crank journals = big con rods
The big con rods are *heavy* (750g!!).
Since the small crank Spit con rod bearing was already
the 'weakest link', this just makes things worse.
(about 50% of the max bearing loading comes from the
mass of the rods and pistons being whipped around at
max RPM, while the the gas loads from combustion are
greatest at max torque)
For well designed automotive journal bearings,
increasing the diameter does not increase the load
capacity (because the rubbing velocity increases in
proportion). It does however increase the friction
losses, require more oil flow from the lubrication
system, and increase the weight of the associated
components.
To increase the load capacity, you have to make the
bearing wider, and/or improve the materials and
manufacturing process.
Here's an article about an improved bearing material
from Honda that allows greater load capacity:
http://g-speed.com/pbh/ae-honda-tech.html#bearing
Carter Shore
--- Mike Chambers <mikech@sprynet.com> wrote:
> Please explain why the big crank 1300 has no
> redeeming features. I've heard
> this a few times but I've never heard a reasonable
> reason why.
> MikeC
>
> > only use a big crank 1300 if all
> > else fails as they have no redeeming features.
> > John Kipping
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