Now that I've acquired some countersinking skills I can get to the REAL problem:
I'm replacing the battery tray in my -8 to accommodate an Odyssey 925 battery. The footprint of the Odyssey battery is not the same as the Gill that was there - it's narrower side to side. So I bought a new battery tray from Van's and riveted in new angle for the new footprint. So far so good.
The tray is fastened to two flanges aft of the baggage compartment 3 holes on each flange (numbered 1-6 in this picture):
The plans call out for AN509-10R9 (10-32) screws going into K1000-3 nutplates on the underside of the flanges. You can see the rivets for the nutplates in the picture.
the builder chose to use 8-32 screws going into K1000-8 nutplates.
I CANNOT fathom why the builder would do such a thing. This tray is right near the elevator pushrods/bellcranks/autopilot. Should the tray rip from it's moorings the controls could get fatally fouled.
Much swearing and cursing.
Ok but now what to do?
I compared a K1000-8 to a K1000-3 and the rivet holes are the same size and the same distance apart. I believe they are interchangable so long as I drill a larger clearance hole for the 10R9's in the flange.
But being a newbie, I don't see how they can be flush riveted in place.
An alternative would be to remove the nutplates, drill the larger clearance holes for the 10R9's, and use stop nuts/cotter pin nuts/ safety wired nuts instead of nutplates. If I did that, and left the rivet holes empty does that somehow compromise the strength of the flange? I'm assuming that the reduced spacing between the larger clearance holes and the rivet holes is not detrimental.
I supposed I could mount a doubler along the underside of the flange fastened by the 3, 10R9's
That's all I can come up with - any thoughts would be appreciated.
(why the !@#$% would the builder do that???)