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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>]