Okay..  Call it what you will.  The aluminum gets overloaded because
it expands quite a bit with temperature.  The lack of stretchiness in
the through bolts causes the compressive load in the stackup to get
high enough to cause the aluminum to permanently deform..  Then the
engine leaks when it's cold.  At least, that's what I remember us
talking about before.

Still wondering at what horsepower level that happens..

Matt-

Only in the earlier engines. Mazda changed the rotor housing  material a few
years ago to a low expansion, high silicon content, aluminum alloy. Shrunk rotor
housings are much less common than they used to be.

It is not so much a question of HP as the guys are getting
800 HP or more out of the turbo charged engines and they are using the larger diameter
steel, stiffer, tension bolts in the bargain. It is a factor when you let
the engine severely over heat to well above 600F around lower spark plug hole.
I am guessing. I don't know the exact temperature when this happens

It is important to make a distinction between creep and temporary deflection.
They have real different meanings in mechanical engineering.

Paul Lamar ...No rotor no motor.

A lot of engines have been killed due to improperly
pinned/dowelled/studded kit mods.
And many high power engines run fine without these mods.
IIRC, Lynn Hannover mentioned his12A NA race motors showed signs of
twisting at 270?HP(Max).
If you are concerned, you might add a thicker reinforcement to the oil
pan flange.
One related hint is to bevel the rotor housing chrome edges to help
reduce contact pressure /
twisting related chrome flaking.
Cheers
Cary

Cary,
I often like your suggestions, but any fooling with the chrome surface will
allow blow-by and early failure in this region.
George (down under)

Hey George;
I agree you don't want to remove a lot of chrome due to blow-by.
The chrome edges are already an early 13B failure point - chrome wear
will reduce
compression and flaking "could" contribute to the death of a seal.
The point is to take just enough chrome to reduce load on the chrome -
never heard an
exact number - 0.0005" ?
One of the folks I heard this tip from was LynnH.
Have you seen pics of his race housings - they look like new after years
of hard use...
Cheers
Cary


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