Mark Steitle wrote:
Paul,
Sorry to bring this up again, but I could use a little help. I recently
ordered TES o-rings from Creavey and they arrived yesterday. The inner and
outer oil o-rings fit perfect, but the outer coolant o-ring is too big by
about a 1/4". Here's a quote from a recent message on this topic which is
where I got my measurements.
<snip>
> 2. outer coolant oring -
>
> diameter = 11.340
> slot depth = 0.062
> slot width = 0.110
> section size = 0.093
This is critical! The proper section size is .093. Not 3/32
as a 3/32 O-ring is bigger in section size than .093.
<snip>
Please explain what is meant by "diameter". The measurement of 11.340" is
what I gave Creavey, but they took it as ID. Now it looks like it is
actually the o-ring centerline to centerline measurement. Is this
right? I didn't know enough to correct it at the time. Hopefully they can
put them in their o-ring shrinker and make them smaller. Would it be
better to provide them with the circumference measurement instead? If so,
what is the correct circumference? In recent postings I've seen 35.13,
35.31, and 35.62.
Thanks,
Mark S.
Sorry about that Mark. I think that is OD and not ID.
Is the engine apart? If so check the dimensions by measuring
the grooves. My slotted end housing is up at the hangar.
11.340 diameter center line is 35.62. 1/4 inch less on
the circumference would give a centerline diameter of 11.260.
11.340 minus the .1 slot width would be the ID or about
about 11.240 inner diameter. The circumference for that
would be 35.31.
You could cut a small chunk out of the outer ring and place the cut
on the cool side or the top of the engine with a little red RTV
silicone rubber and you will be fine. Or mail the outer back
to Creavey and asks them to make a set 3/8 inch smaller in circumference.
Also perhaps they can tell you what kind of glue they use to join the ends.
It is best if the O-ring is slightly undersize as you can pre stretch
it on a plywood board.
35.13 is probably the right circumference number.
Creavey should know by now what the proper sizes are.
Also mic the section of the outer ring and make sure it is
.093 and not any larger.
I may be forced into stocking these O-rings if we continue to be confused
about the proper sizes. I did not really want to go into business again
but it looks like that is what is happening with the intake manifold parts.
BTW Jeff Chrysler if you are reading this Mazda will sell 18,000 rotary
engine powered
RX8's next year in the US.
Paul Lamar
Here is how to double check my work. We will do a little reverse engineering.
The O-ring grooves are two half circles connected by straight sections
to form sort of an oval.
Measure across from side to side on the end housing to the inner edge
of the O-ring groves This then is the inner diameter of the half circle.
We will call this dimension SSL. For the inner O-ring this diameter is 7.5"
Outer diameter is is 9.75". These form two circles of 23.562 circumference
and 30.63 circumference. C = D X Pi (3.1416)
Measure the distance up and down to the inner edge of the O-ring grooves.
For the inner O-ring groove this dimension is 9.75 (confusingly).
Outer o-ring groove is right on 12 inches.
We will call this dimension VL for vertical length. VL-SSL gives us
the length of the straight sections. We have two straight sections
9.75- 7.5 or 2.25 inches in length for the inner o-ring slot
and 12 - 9.75 or 2.25 for the outer O-ring slot straight sections.
There fore the inner circumference is 23.562 + 2.25 + 2.25 or 28.062".
Close to the number we got below. Divide by 3.1416 to get the
equivalent diameter.
For the outer o-ring slot the circumference is 30.63 + 2.25 + 2.25 or 35.13.
Also close to the number we got below.
Now to be real precise you must repeat these measurements for
the outer O-ring slot grooves.
Or we could merely take these numbers below as the center line
numbers or OD numbers. In any event you want to err on the small side
as you are going to cut pieces of plywood the exact size
of the inside wall of both slots and slip the o-rings over
this plywood form for for a few days so they will take a set.
Other wise you will play hell getting the o-rings to lie flat
in the grooves when you assemble the engine.
Paul,
Thanks for the prompt reply. I'll take some measurements tonight and
call Creavey in the morning to determine the best course of action.
Would you be comfortable flying with your family in an engine with
spliced o-rings? Not sure that I would. Hopefully, Creavey can fix these.
Mark S.
Yes. It would not bother me. The nasty hot chemicals are generated around
the combustion chamber and near the exhaust so the inert teflon jacket
is not all that important on the cool side of the engine.
The stock O rings are made with red RTV with a teflon coating
on only one side....the combustion side. They use cheaper
neoprene O-rings in the outer grooves. When you are making 100,000 engines
with eight water O-rings per engine every dime counts. That's 800,000
O rings or $80,000 dollars profit.
Lynn has been doing essentially the same thing with his home grown
teflon hook up wire O-rings apparently for several years.
Paul Lamar
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