An interesting fact - there are two versions of 1300 engine, the Mk III
Spitfire one with small bearings, and the Mk IV one with large bearings
(commonised ones from TR5 and 6). Not only do the large bearing version
engines not produce the same power as the small bearing ones - they also
have a much shorter bearing life. (Uk versions are better because apart from
crank bearing size the engines are identical). The only factor in the
shorter life must be that the speed across the bearing is higher with a
bigger diameter - think what a six cylinder would be like with smaller
bearings.
John Kipping
----- Original Message -----
From: <Gt6steve@aol.com>
To: <FOT@autox.team.net>
Sent: Wednesday, May 05, 2004 2:25 PM
Subject: Bearing theory
> Amici,
> All this bearing talk of late has me exploring the empty caverns of my
mind.
> While pondering the quoted PSI ratings for the King bearings I realize I
> have no idea what my engine requires. It seems there's a factor missing
from the
> equation. I know surface area of the piston but what the hell is a
> reasonable figure for the combustion pressure applied to the bearing.
Surely it's not
> directly proportional to CR. Or is it? Is there a general value
accepted?
> What if my killer head burns better than the stock one? Higher pressures
> applied to the bearing obviously so without knowing your exact Volumetric
> Efficiency and the pressure produced in the chamber how can we guess a
suitable
> bearing? Disregarding all the shiny bits in the filter.
> Then, how does the surface speed of the bearing factor in?? Would a ten
> percent reduction in surface speed (or one or twenty) be more significant
to the
> bearing life?
> Enquiring minds want to know...Steve
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