Ed Anderson wrote:

Hi Paul,

    I took your suggestion and made some measurements for the inner coolant
"O" ring.
The "circle" part of the curve has a radius of 3.95", as best as I could get
from the old geometry trick of find the center of a circle using arcs of a
compass (drawing type).  The linear portion was 2..425".
So circumference C = Pi*D = 3.1416*3.95" =24.82" plus each side of linear
portion (2.425 x2 =4.85") and adding the two values I get 29.67" . Taking
that as the circumference of a circular "O" ring gave a diameter of 9.444",
I rounded to 9.50" which with the grove depth being 0.071" (on my used
housings) I selected 1/8" thickness (also matches my recollection of the
thickness of the Hayes rings).

This all led to AS568A-272 part number 9319K289 from McMaster at $11.54
(quite a bit cheaper than Hayes $25 - assuming of course its the correct "O"
ring).

I plan ordering one just to see if it fits.

Thanks again

Ed Anderson

Ed,

A trick I use when reverse engineering (like you are doing) is to consider that
the guy originally designing it probably had a relatively free hand at selecting
dimensions so is likely to have selected even measurements where it didn't
make any difference.   For instance - you measured the first radius as 3.95".
I'd bet that the drawing dimension is in millimeters, and 3.95 converts to
100.33
mm, so if you have much doubt about the accuracy of your measurement,
it might actually be 100 mm.  The other dimension works out to 61.595 mm,
pretty good chance that it is actually 61.5 or 61.6 mm.   Also consider that
some dimensions are driven by other dimensions and just work out to some
oddball number which has no significance.   No big deal, but some times it
helps a little

Also, I think that certain items (o-rings included?) have been stadardized on
mixed units because the US measurements were the first on the scene and
have not been replaced.  I think this is the case with o-rings having inch
based cross sections as std (.0625 (1/16th), .125 (1/8th), etc) but probably
mm for length (circumference) in metric countries.  FWIW.

Bill
Long EZ builder & pilot
mechanical engineer

 
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