<< Picture after I get it
 powdered coated. >>

Paul,
discussion of cracked engine mounts on the canard-aviators forum brought out
a recommendation against Powder coating an engine mount because it is likely
to make it impossible to detect cracks visually. The coating tends to stay
intact even though the underlying metal has cracked.
Ed.           pebvjs@aol.com

Yes I have heard that before. I personally don't buy it. But to each his
own. 

Motor mounts are designed to extreme limits. Namely six G in a 
severe pull up or hard landing. Or if the engines suddenly seizes
a high torque load is applied. As such the failure mode is not likely
to be cracking. The failure mode is likely to be bending when the 6 G occurs. 
Most of the time the stress is sleeping by comparison.

The rotary is low vibration so a large diameter tube (as opposed to a long, 
small diameter bolt) resonating in the guitar string mode is unlikely but 
possible I guess. The Mazda torque forcing frequency is zero to 200 cps 
to 6000 RPM. Anybody care to calculate the resonant guitar string mode 
for a 3/4  inch diameter, 0.049 wall steel tube 20 inches long?

Paul Lamar
 
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