There is almost no perceivable space in the bores at idle setting. I
agree with the suggestion of drilling 3 small holes (one per runner) in
the slide. I had considered doing that to help during idle.

As for the air leak... During idle, the 2" hole in the Teflon slide for
rotor #1 moves very close to the hole in the frame for the cable. This
could provide a path for the air to bleed into the #1 rotor causing it
to run lean. This may account for the higher than normal MAP as well as
a mismatch in air-fuel mixture during idle. It would become less of an
issue as the throttle is opened, exactly as I am experiencing. I
suppose I've got it tuned as well as possible, but with this condition,
I don't see how I will ever get it to run well at low MAP. It shouldn't
be too difficult to install a small seal. It sure wouldn't hurt
anything. I could probably stuff a small piece of shop towel around the
shaft for a down-and-dirty test. If the idle improves I'll know that
I'm on to something.

Mark S.

A seal would be worth a try in that case.
For future use do you have room to make the slide an inch or so longer?

Paul Lamar



Paul,

I guess it is possible (anything is possible), but not really practical.
Ref. *Marks pics 2009-2010 287.JPG *showing how close to the firewall
it is now. The other end is up against the oil cooler. So, what did
you have in mind?

Mark

One inch longer on the fire wall end.

But try the seal first.

Do you have Teflon on both sides of the slide?

That should help seal the top and bottom in case it is leaking
around the edges. Also what is the exact gap at idle?
I can figure out the area.


Paul Lamar

Paul,

I'll try to measure the gap on my next trip to the airport, which will
be next weekend.

Previously, I had sealed around the edges with Hylomar. I also added
more screws around the perimeter. I had it apart last weekend to add
an idle stop (should have done that in the beginning). I didn't have
any Hylomar on hand, so I reassembled without it. That may be
contributing to the current problems.

Do you recall that originally my Teflon slide had way too much
friction, so I added a sheet of .032" Teflon on the downstream side.
Well, this stuff flows over time allowing tolerances to change. I've
ordered a sheet of .032" high temp Garolite (G-7). This should
provide a slick surface for the Teflon to slide plus be more stabe
structurally.

I only plan to make one change at a time so I will know what helps and
what doesn't.

My concern with the "Holley float bowl" idea is that every Holley carb
I've ever owned has leaked fuel sooner or later. With the intake
located directly over the hot exhaust, I would not be comfortable with
that. It would definitely need a catch tray.

Mark


OK NOW I remember. You have a REAL teflon slide.
There were or are two different tolerances for sheet
Teflon. The lower cost of the two had very lax tolerances
on the thickness. Perhaps plus .0032. and minus .015".
A 12 by 24 sheet cost only $90 :)

That would explain the high force.
Since you added the spacer to give more clearance to reduce the
force that would also lead to many air leaks in and around the inside
of the slide throttle. Take that thick Teflon slide out of there
and replace it with 1/4 inch thick aluminum plate and thin .032 Teflon
liners. This also makes a much cheaper slide throttle as all that
Teflon
is expensive. The precision ground blanks stuff is about $250 for a 12
by 24 sheet 1/4 inch thick. 3/8th thick would be $385. Tol is +/-
.005.

As per these pictures. Note the aluminum slide in the slide throttle
kit picture. The tolerance on aluminum sheet is probably closer
to plus or minus .001. Thanks to C. Smith for these pictures.

Don't do the Garolite thing. It is useless as a gasket.

1/32 thiick Teflon is better. The tolerance on the cheap
1/32 stuff is +/- .003 and a 12 by 24 sheet is only $12.

For years Mazda rotaries had 4 barrel carbs mounted directly
over a thermal reactor to reduce unburned Hc. For some strange
reason they did not catch fire. I am not sure if it was too lean or
too rich. My guess is the fuel falling on the red hot reactor would
vaporise instantaneously. It seemed to me that would be an explosive
mixture but it never seemed to happen.

The RX2 had a tray under the carb. Here is a picture.

Paul Lamar

Paul,

The piece of Teflon that I had added was not to take up any gaps, but
was to create a Teflon-to-Teflon sliding surface. And it worked very
well, except that Teflon flows and deforms over time. You could see
Teflon oozing from between the layers of aluminum where the screws are
located. Recently, when I took it apart, there were three "bulges"
where the slider holes are positioned when the throttle is closed. I
recently took an Xacto knife and removed the bulges, which may have
exacerbated the vacuum leak. I don't see how making the slide from
aluminum would resolve either of these two issues.

On a side note, when I first added the Teflon sheet, I also removed
some material along the top of the Teflon slide, but left a small bump
on each end to keep it in place. My thought here was that when
heated, the Teflon slider was expanding enough to cause binding on the
aluminum frame top and bottom. This may have helped more to relieve
binding than the additional sheet of Teflon. Maybe I should try
removing the Teflon sheet completely.

I've also considered making the downstream plate from SS as this would
reduce the COF without the material problems associated with teflon.
Machining is the only issue I can see with the SS side plate, but Bob
Darrah can handle that for me.

Mark

I am not following you Mark. Are you saying the 1/4 inch thick
Teflon slider is bulging into the the 2 inch intake holes?

Can you send me a sketch?

Coefficient of Linear Thermal Expansion for Teflon
(x 10-5 in./in./°F) 7.5

That is ( I think) 0.000075 inches per inch per degree F.

At 100F that is 0.0075 or 7 thou per inch.
At 2 inches wide would be 2.015 or fifteen thou wider.

6061 aluminum is 13 micro inches per inch per degree F

A micro inches is .000001 inch

So it is .000013 inches per inch per degree F.

So at 100 F that 0.0013 per inch. 2 inches is only 0.0026
wider. Not much difference. You must have cut that Teflon
exactly. Did Bob machine it?

I guess that looks possible unless I am making a mistake
here.

Mic your Teflon slide in a few places and see how uniform
it is.



Paul Lamar


Paul,

For clarification, the .032" Teflon is what deformed over a period of a
year or so. There were three bumps where the holes in the teflon
slider rested when at idle or stopped.

Also, the .032" Teflon (which was captured between the frame and the
downstream side plate) squished out at each screw location. This has
caused the downstream aluminum plate to deform. As a result, I don't
feel that Teflon is a good material to use here.

Keep in mind that the slider gets sucked towards the downstream plate,
especially at low MAP settings.

Also, the Teflon slider is .380" +/-.

Mark

The thickness tolerance on 3/8 Teflon is +.038" and minus .019".
That is a bunch. Lots of room for leaks between ports.

My theory is the non uniform thickness of the Teflon slide is
allowing air to leak from port to port. The intake surge or intake
pulse is 120
degrees out of phase for a 3 rotor. All sorts of weird things
can be happening in there. You will see that when you get it
instrumented with the high speed pressure sensors.

I still say dump the Teflon slide and replace it with uniform
thickness aluminum slide.

OK maybe we need the etched (bondable) on one side .032 Teflon and
epoxy it down to the aluminum covers. Better yet you can also buy
that in .015" +/- .002" thickness. Less chance for cold flow.

Either anodize the covers first or get the aluminum etching kit
from a boat supply shop. Here is a jpg of the etching stuff you will
need.

Teflon is the only material that provides the needed low coefficient of
friction.

What is the thickness of the downstream aluminum plate?

You can make a doubler out of .25" thick aluminum
1/2 inch wide bars to spread the clamping loads from the 10-32
screws. That is a common problem in oil pan bolts. McMaster sells
aluminum bar stock in that size (1/4" thick 1/2" wide) for about $8
bucks for 8 feet long.

I will change the slide throttle instructions to include those
improvements. I really appreciate all the long term R&D you are doing on
this Mark. You are a real pioneer.

Paul Lamar


Paul,

I like the idea of bonding the .015" Teflon to the covers. I may give
that a try after sealing off the big leak around the cable.

Another thing that I found that I haven't mentioned is the .032" teflon
had puckered around a portion of the #3 port to where it may have
interfered with the slider closing completely. This was only seen on
one port and may have been caused by a sharp edge. Anyway, as I said
earlier, I remedied this by cutting away some of the teflon.

I had another idea to reduce friction. Could it be built with a little
excess clearance between the slide and the two sides and then use
Teflon o-rings to provide a seal around each port. The o-ring would
have to be racetrack-shaped so as to not catch or snag as I've described
above.

The o-ring groove could be made with a wood router using a guide
block. This would make for minimal surface tension between the slider
and side plates.

Mark

I figured out why you are getting .032 Teflon bulges in the area you
are talking about. I looked in an old book I had on aircraft carbs
called "Aircraft Power Plants" published by Northrop Aeronautical
Institute back in 1948. It has an excellent chapter on carburetters
theory and practice. It reminded me at idle the air velocity is very
high in the area of the slide throttle that is still open during idle.
More importantly the air pressure is also very low. That has sucked
the Teflon away from the metal cover. Therefore bonding it to the metal
is essential.

Here is some scans from that book.

IMHO you don't need the O-rings if the slide is close tolerance.

If the edges of the slide catch one and drag it out of it's
slot it could be disastrous.

Here is Mark's slide throttle p-port 3 rotor engine for the new guys.

Paul Lamar


Can we get an aluminum throttle plate coated in Teflon, just like a
non-stick skillet? Should have very uniform thickness. You can buy a
Teflon coated skillet for less than $10, so it shouldn't be an expensive
process.


Regards,

Matt-


Yes, you can get your finished slider coated with Teflon.  There is also
a less effective method where you can paint on a Teflon solution.

Mark LaPierre
Registerd Linux user No #267004