Originally Posted by John-G
Thinking about it Dale is probably right about 8mm being the size for the hex socket needed and it is in the HF hex set.
I am also remembering 8mm
What works really well is to purchase just an 8mm ball end allen wrench and cut of the short "L" leg and insert it into a socket.
That gives you an approx 4" long skinny extension beyond your socket.
BTW, only the very first cooling shrouds produced required modification to access the upper left bolt. Any produced in ~2009 and later will require no modification.
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Formerly of Van's Aircraft Engineering Prototype Shop
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RV-6A (aka "Junkyard Special ")