BIG SNIP

I'll have to look that up. The very first batch I got was from All

O-rings.

Bad place as they were trying to obscure source and part numbers.
I think I did get some from McMaster Carr but not sure
if yours was among them. The last batch I got directly from Creavey
and I think those went into your engine.

The outer slot has an area of .13 by .070 or .0091 square inches.
so the radius squared would be .0028966.... working backwards.
The square root of that is .0538.

So the largest section diameter to fill the outer slot would be

double

that or 0.107640. That lends credence to Bill's theory as a 3/32
section diameter ring is not .096 section diameter but is about
0.11 section diameter or about 14 thou larger (.014).

And then you have the O-ring tolerance on top of that. Some might be

0.005

under and some might be 0.005 over. Also any crude in the slot will

not

help matters. Make sure the slots are spotlessly clean.

Perhaps Mazda themselves ran into Bill's contention back around 88

and

that is why some housings cracked in this area. Perhaps they reduced
the section dimensions on the stock O-rings slightly.

This is why we call them experimental airplanes.

Bill, do you happen to know what the coefficient of thermal expansion
is for red silicone?

The bottm line is measure your water O-rings and make sure they are
less than .093 +/- .005 section diameter. Particularly the outer
one.

Paul Lamar

Would I be correct in assuming this could be an infant mortality
problem. In other words, if it didn't show up soon after engine
assembly, one might be ok?  My engine was running it's hottest
the first few flights after overhaul because of plugged rads.

Perry Mick

I would say that was a correct assumption. At least I hope so.
Our original theory on why some of the 88-89 O-ring lands cracked
was because of quality control... casting core shift. This may
still be a factor.

I know it is cold up there now Perry but what are you now seeing in the
way of oil temps and coolant temps?

Paul Lamar

I think you're right Perry.  It would fail on the first full temperature

thermal

cycle or soon thereafter, by cracking the first time then failing to

seal soon

thereafter (immediately?). Could be that some of the castings are

weaker,

but really, you can develop nearly unlimited stress if fully trapped and

heated

enough.

Bill Freeman

Tom Kimsey sent this picture of the broken casting and it looks like
it had plenty of meat around it.

Paul Lamar

Group,

<Maybe I should call Hayes Rotary and ask them for sources and part numbers
as they put it TES o-rings on their rebuilds.

Ken Gillanders

 
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