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Message
Hi Guys,
Just to set the record straight, under normal
operations (N.A. engines), and sensible revs (under 8,500), there is
little or no cogent reason to do this mod.
However, in full house race engines with BIG
revs (10,000 + RPM), in high boost engines (1 Bar + boost), or where
"Giggle Gas" is used as in Ken's case, it's not a bad idea. The main
cause of the problem is crank flex under high load conditions, which
allows the rotors to cock in the housing, and also wedge the oil film on
the rotor journal. So it's not a bad idea, and in fact I do
both recommend it and practice it myself in these apps.
Obviously, a centre bearing 2 piece crank will
eliminate the crank flexure. I have found over the years that 15 thou is
more than adequate, but 20 thou is quite OK.. Doesn't seem to affect
compression at all. I normally taper it away to nothing down to the
outer oil control ring groove on both sides, ap personal preference.
Easily done in a lathe, and I prefer to grind rather than
machine (a tool post grinder in the lathe is the go if yu have access to
one) to avoid interrupted cutting around the corner seal holes. That
way, you get a really nice finish without any chatter marks. Make
sure the grooves are de-burred if you do it.
There is an additional advantage. If you
happen to lose oil pressure, (even with a 2 piece centre bearing crank),
the rotor has a natural tendency to cock on the stationary gear due to
lack of the oil film on the crank journals. If you have clearanced the
rotor tips, then there is less likelihood that the corner & side seals
will be swaged into their grooves. In reality, loss of oil pressure
is usually catastrophic anyway, and the rotor usually needs to be replaced
as the raised lands (the rotor gear and the land on the opposite side sit proud
of the actual rotor faces) usually cop a hiding and end up cleaning up below
spec.
My couple of Brass Razoos for
today,
Cheers,
Leon
----- Original Message -----
Sent: Sunday, April 17, 2005 12:01
PM
Subject: [FlyRotary] Re: New rotors, New
housings
That's off each side, Rob at
Pineapple racing takes 20 thousandths off each side but I figured the 15
should do it.
Ken
Hi
Ken,
Why is it
that you do this? I've never heard Leon, Lynn, or Bruce
mention this being necessary.
Cheers,
Rusty
(waiting for contractor season, so I can start shooting
them)
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