Miata Mailing List: May 1996, Message #50
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   From: Tom Manson 
Subject: Re: More AutoRotor Experiences?
   Date: Wed, 1 May 1996 20:27:13 -0400

On Wed, 1 May 1996, Greg Bassett wrote:

> We've been back to Corky's for a few new items:  
> (1)  2 brackets developed cracks and were replaced.  The main bracket
> holding the S/C to the block was cracked by over-torquing the bolts.  A
> beefier bracket was put on in its place.  The small bracket that holds the
> air cleaner and mass air sensor assembly on also broke.  this bracket was
> flexing and causing the assembly to bump against the fender top (inside the
> car) during hard braking, and hard right hand turns.  A new bracket was
> developed that solved this problem.

Greg this is somewhat interesting.  Bolt torque is determined by bolt 
size (thread pitch and bolt diameter) and its purpose is to establish a 
fastener pre-load thus prevent back-off.  If the bracket could not 
withstand the torque applied to the bolt, the bolt was improperly 
selected in the design phase.  Use a smaller bolt.  If the threaded hole 
was aleady in place (tapped into the block for instance) and you are 
forced to use that size, then you will have to redesign the bracket to 
withstand the bolt torque.  But don't just arbitrarily add mass to the 
configuration because you can end up creating a worse load due to more 
severe forces during vibration.

I trust that Corky has a mechanical engineering background and will 
recognize these concerns, but if you are doing the 'analysis' and 
'design' (oops, I'm assumed you did not have the ME gbackground) be careful.

Later,
Tom