>> The Teflon I get varies in thickness from batch to batch, even though
>> it
>> is
>> all 3/8" nominally. I specify the clearances and provide the Teflon to
>> the
>> machinist, so the spacer thickness varies from batch to batch. I think
>> the
>> Teflon in the throttle you have is 0.400" and there is no clearance >>
built
>> into the spacer, so Teflon 0.390" would be good, if you can find some.
>> I
>> think the side clearance is not critical as long as there is enough
for >> a
>> pure throttle. A carb might be different.
>>
>> Incidentally, coarse 3M scotch brite works great for deburring Teflon
>> after
>> machining. It doesn't tend to gouge like a deburing tool.
>>
>> Good luck. I think you will have a difficult time with sealing.
>>
>> Incidentally, my machinist friend needs a carb for his truck. He is >>
also
>> thinking of doing what you propose, only with a single hole. I'll let
>> you
>> know what he finds out and vise versa.
>>
>> Doc Custer
>> Retired Software Engineer and sometime Audiologist
>>
>> Good advice. Thanks Doc.
>> Well if worse comes to worse and I don't have room for a race track
>> shaped groove and Teflon O-ring around the slot I could go to a 1/2 >>
inch
>> thick slide. I was thinking of a flat or wave spring, like the apex >>
seals,
>
>> under
>> the Teflon slide.
>>
>> BTW the O-ring groove is not shown yet in these 3D's.
>>
>> Why don't you guys fly cut the Teflon to all the same thickness?
>>
>> Paul Lamar ...No rotor no motor.
>
snips...
>
> The kind of spring I was thinking of is shaped like a recurved bow as
in
> archery. Put two or three in the bottom and they will force the Teflon
> up to
> help seal the sliding joint.
>
> I hope the O-ring works. And you have a lot of success. How are you >
going to
> deal with the left over fuel in the system after the engine shuts down?
> Maybe a positive shut off valve right at the slide throttle?
>
> I know my machinist is interested in the problem. As I mentioned >
previously,
> he plans on making one for his truck instead of buying a new carb.
Would > you
> like to be put in touch with him?
>
> Doc Custer
> Retired Software Engineer and sometime Audiologist
snips..
This addresses the sealing and expansion rate of Teflon issues.
Maybe this is what Doc had in mind. Larry suggested we machine the springs
in the spacer all in one operation using 7075 T6. A high strength aluminum
alloy. I used to build race car wings out of it and it is like razor
blades.
I will contract Larry to make a new spacer and Teflon slide for the
all mechanical low pressure fuel injection.
BTW It recently became crystal clear to me the difference in a venturi
and intake manifold pressure. The venturi does a much better job of
measuring
the mass airflow. Not as good as a mass airflow sensor however. I digress.
Consequently the new Teflon slide will be 1/2 inch thick instead of
3/8th and the large holes will have a slight venturi shape.
We are building a new 7075 T6 spacer anyway. The rest of the slide
throttle
parts will be the same as what Doc is producing.
Paul Lamar ...No rotor no motor.
Paul,
If Teflon is difficult to machine and sheets vary in thickness, why not use
an aluminum slide with Teflon buttons.
George (down under)
Because it would not seal.
Paul Lamar ...No rotor no motor.
I don't know if temperature affects teflon, but i have learnt not to drill
fixing holes in long wear strips late on one day and try to rematch up the
holes in the mating part the next day, only to find a miss aligment. I can
not remember if it was nylon or teflon we were working with. At first we
though we made some kind of mistake but we used the hole centers in the
mating parts to witness through onto the wear strips. So we gused that
temperature diffrance may be the cause and after leaving the wear strips to
heat soke in the office for an hour or two out thay came and on they went
all fitting spot on. There was a large thermal expandtion with only a 10 to
15 deg C difference between office and factory.
Maybe something to look at if it is causing problems.
Jim
Melbourne Australia
Yes Doc pointed that out. We are designing around it.
Paul Lamar ...No rotor no motor.
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