# Engine mount holes



## mysons69 (Mar 3, 2012)

Has anyone drilled and tapped any engine block motor mount bosses? If so, what is the proper depth? I'm assuming one inch based on the others being one inch, but I really don't want to go too far, so confirmation from anyone would be great, if possible.
What we have is the '77-79 481988 XX block, and there are three 7/16-14 holes drilled in the block. Of course, none of those three are the two we need to properly mount the engine in a '69 GTO, therefore the need to drill & tap the other two. Doing so will make it like the 455s (or is it all 70-76 blocks?) in regards to the motor mount holes. 2 & 5 in the link below are the bosses we need to drill and tap.
http://www.butlerperformance.com/Articles/Engine_Block_Ident_Ames.jpeg
Thanks.


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## mysons69 (Mar 3, 2012)

Just an FYI in case anyone needs to know.

I drilled and tapped the four bosses in question, each to a depth of 1", just like the others that were already tapped. No problems whatsoever with the 1" depth. The proper drill size for tapping to match the other holes was 23/64, then tap away.


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