- The Response - What do you mean when you say
"will not perform to its potential?" Is there something
that's not working correctly? Attach a degree wheel to
the crank and check the port timing - it will help you
sort out your options - and it just might give you a
better idea of why it doesn't seem to perform well. What
rods are being used in that motor that are 4 mm longer
than standard? The RD 400 rods are a pretty standard
replacement for the Banshee rods - especially when making
a 370 cc long rod engine. The RD rods are 5 mm longer
than the Banshee pieces. Boring the cylinder out to 66
mm, using Blaster pistons allows for an almost perfect
set up - actually removing a small amount of material
from the bottom of the cylinder is what's needed. Re cut
the Blaster piston tops to make them work well.
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- Decking the motor - by itself - does nothing to the
port timing - that is - removing material from the top of
the barrel. Removing material from the bottom of the
barrel will lower the ports. It's pretty unusual for a
barrel to be decked that much - and even more unusual on
a Banshee which is a zero deck motor. Especially when you
consider it is using longer than stock rods. Without
appropriate piston pin offset to compensate it would rise
above the bore at TDC - removing additional material from
the top of the barrel would worsen this condition. If
this motor has long rods and a spacer plate to compensate
for the additional length, the port timing would be the
same as it started. There would be no timing changes do
to the increased rod length - as long as the spacer plate
+ additional gasket = the added length of the rod. I
don't get why the barrels were decked at all.
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- The edge of the piston can come above the cylinder
liner at TDC in a 2 stroke engine as long as the head has
an additional relief cut for this. If the top ring
doesn't cross the edge of the cylinder it will work ok.
Sometimes fixes are made this way. Is there a chance that
there is a piece of information missing here?
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- Rick
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- I agree with Rick, sounds like
somebody used this motor as a science experiment or
something. Thought it would be neat to throw a bunch of
stuff at it and see what it would do. Should probably get
some new barrels and start over. The long rod Banshee
isn't a bad set up. Like Rick said, use the RD 400
(However Hot Rods might be coming out with an application
specific long rod for the Banshee). In fact I talked to
Tony at Tony Doukas Racing (the guy the built my crank)
and he is trying to get Kurt to build long rods for these
things. Anyway, I think that your friend needs to get new
jugs, stick with the long rods and blaster pistons, this
is not a bad set up in itself, but the cutting of the
deck and adding a spacer to compensate sounds pretty
"mickey mouse" to me. Later.
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- Eric
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- The barrels have been ported
twice by two different people. The first time the BOTTOM
of the barrels were decked 3 mm. This lowered the port
timing. My question is would it be better to add a 3 mm
spacer plate in addition to the new long rod plate(we are
now using +5 mm rods with a standard piston) or to just
raise the port heights an additional 3 mm to compensate
for the decking? We are trying to get the motor to run
right with the new port specs.
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- Get a Blaster piston to go with
the long rod. This will allow you to take advantage of
the long rod. Don't put spacers in, what is the point of
decking the barrel, then putting a spacer in to put it
back where it was. The only way to get the full potential
out of this motor, since it was probably set up to run a
long rod with a blaster piston, is to get a set of
Blaster pistons. This will move the wrist pin up far
enough on the piston to alleviate the need for a spacer
plate. You don't want a spacer plate, you want a set of
Blaster pistons. I would guess that you could add a 3 mm
spacer to make up for the barrel decking, this will
probably help a ton. Good luck. Later
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- Eric
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- Alright, two different people have worked on this
motor. The first was an idiot, the second was pretty
decent. We cannot use blaster pistons because we cannot
go that big at some of the tracks(legally). So that is
why we use the spacer plate and the stock pistons. We
found out after all this work was done(port, rods etc.)
that the first guy had decked the barrels. So this was
throwing off the port timing, evident by the performance.
We cant just get new jugs, to much into these, we just
want these to work.
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- Here's what I would need to figure this out better -
a degree wheel reading - the port timing. With the lower
barrels and the long rods with the Banshee pistons, I'd
guess the pistons are hitting TDC at about the handlebars
<g>.
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- Give me something to work with here - otherwise get a
few base plate spacers of different thicknesses and start
testing.
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- Rick
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