Mr dan ruggirello wrote:

I posted earlier (@ flyrotary) that I was skeptical
that the tension bolt issue was vibration since my gut
feel was the bolt was much stiffer than 110hz (6500
rpm).  Well, I just estimated the 1st mode natural
frequency and low and behold, I calculated a frequency
of 150hz.  Too close for comfort!!!

Specifics:
fixed at one end, pinned at the other
diameter: 10mm
length: 273mm-10mm ~263mm (10mm thread enguagement)
E: 30 msi
I: 1.18E-3 in^4
density: .30 lbs/in^3

Yup, very likely it's vibration/fatigue.  Now my
question is if the RTV or shrink wrap is effective and
reliable......

I will probably calculate a fatigue life on the stock
bolt, use the RTV and replace the bolts every so often
based on fatigue life or go to a higher strength bolt
(given it meets the fatigue life) for added margin of
safety.  (I think I saw a higher strength after market
bolt).  This seems like a case where the bolts were
engineered for an average automobile environment where
continuous/frequent high rpms are not a design
consideration.

I am not that familar with the bolt, anyone know what
the stock bolt material is?  Is the bolt diameter
equal to or less than the minor thread diameter?

Dan

Thanks Dan. Funny you should mention that as Richard and 
I were talking about it on Monday at his place. Some are cut down
and some are full diameter 10 mm (new ones). I have no idea what 
the material is but I am sure it is some sort of high strength 
steel.

BTW Richard is thinking of offering a service to check used
bolts for cracks by measuring the resonant frequency.
New bolts are $17 each from Mazda.

Paul Lamar
 
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