Sam, I just took my PDWA apart from my 1972 TR6 and the piston looks
torpedo
shaped on both ends as you described. The markings on my PDWA are: 4324/641
and 4L21. Mine measured:
groove inside diameter = 0.194"
groove width = 0.084"
bore diameter = 0.312" (so effective groove depth = 0.059")
I've read that o-rings should have a 10% diameter squeeze to seal,
so we need an o-ring with a minimum cross-section of 0.059" x 1.1 =
0.0649".
A "0" series o-ring has a x-section of 0.070" +or- 0.003" (0.067"-0.073"),
so a "0" series o-ring should provide an adequate seal.
Possible "0" series o-ring sizes are:
-008 uniform dash size: id = 0.176" +or- 0.005"
-009 uniform dash size: id = 0.208" +or- 0.005"
The -008 size is slightly smaller than the shaft and would be stretched out
slightly resulting in a snug fit on the shaft. While this will reduce the
x-section diameter slightly, the change should be very small and not cause
it to be less than the minimum required for a good seal.
The -009 size is slightly larger than the shaft and would be a loose fit.
This will require the o-ring to be compressed more when inserted into the
bore. The additional compression may be a problem when assembling the PDWA.
As the piston is inserted and the o-ring passes under the switch hole in
the PWDA body, the o-ring will want to squirt out the hole. If care is not
taken a small chunk of the o-ring will be cut from the o-ring.
I don't know which is the correct one to use. But I've decided to use the
-008 size (in Ethylene Propylene of course).
Can anyone tell me if I've made the correct choice.
Wayne Whippo (Digest mode)
Boulder, CO
72 TR6 CC81472UO
>TRDOCTOR@aol.com wrote:
>
>Listers;
>I got around to taking the PDWA apart in my '6 today with O-rings in hand.
>There is only one problem; they are the wrong size. The ones recommended
>were:
>ID- .375, OD - .250, Width - .070
>These are way too big. The markings on the PDWA are:
>4324/641, and, 51K27.
>Near as I can tell, the size I need is:
>ID - .196, OD - .312, Width - .096
>Also, my piston is very different from the one pictured in the VTR web
page.
>There are no circlips on it and it is a kind of torpedo shape on both
ends.
>When I pulled it apart the O-rings in it were kind of sticky (possibily
from
>the silicone?) but otherwise looked ok. There was no fluid where the
switch
>was located. I will go to the local seal supplier tomorrow and see if I
can
>find the right O-rings for my application.
>Any comments?
>
>Samuel R. Clark
>Green Country Triumphs/Jaguar Enthusiast's Club of Oklahoma
>VTR South Central Regional Coordinator
>TS45355L O
>CC82030U O
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