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     Marv,

     

     You will "squash that insulation big time" using the approach in the

     manual.  I didn't like the idea and I wanted a perfectly flat SS

     firewall when finished.  The way I accomplished this was to make

     spacers which were inserted in the Fiberfrax every place a bolt passed

     through.  For the six engine mount bolts I stacked up AN970 washers to

     equal the thickness of the Fiberfrax and riveted them together.  For

     all other bolts mounting hardware to the firewall, I machined

     stand-offs from aluminum rod.  The three layers of Fiberfrax were

     glued together and cut to size.  Then I transferred the mounting hole

     patterns and used aluminum tubing to stamp out holes in the Fiberfrax

     to accept all of the stand-offs.  You have to know where all of your

     mounting bolts are going to be located, so I waited to very near the

     end to install my SS and Fiberfrax.  In the mean time I had all of my

     firewall forward items installed on spacers to position them as if the

     Fiberfrax were installed. I didn't glue in the Fiberfrax or the SS.  

     They are merely clamped in place by every bolt passing through them

     and could be removed and modified, if needed.

     In general, it is poor practice to have soft, compliant materials

     being compressed by critical fasteners.  In the firewall case, we also

     have a sheet of plywood being compressed. So, no matter what you do

     with the Fiberfrax, you do not have an ideal joint.  Torque on the

     engine mount bolts should be checked regularly because these compliant

     materials can creep and cause loss of clamp load.  

     You will want to stack at least 2 AN970 washers under the nut

     otherwise the nut will want to pull through when torqued.  AN washers

     are not particularly strong and a single AN970 washer cannot

     sufficiently distribute the load when compressing a plywood core.  

     

     Chris Zavatson

     N91CZ

     

     -----

     Marv,

     You can post the above.  I didn't know how what would happen to the

     attachment.

     Chris

Attachment Converted: "d:\eudora\attach\chris.bmp"



[Thanks for the detailed explanation and the photos... looks great.  I'll

upload the pics to the LML homepage Attachments area later tonight.  <M>]