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I am mounting my firewall on my QB5 and I am struggling with several things. One, the top bushing for the engine mount is 5/16 instead of 3/8th.Can I ream that out? Also when I line up the firewall the flanges at the bottom are above the airframe tubing. Should I grind those down?
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I start with the top center bolt hole and reamed it out. Then top left/right and moved my way down making sure it was level and straight. I had to grind/cut the flanges at the bottom. The flanges were getting close to the top rivet.
Travis
Travis M
Kentucky
Bearhawk 5 Quickbuilt Kit Plane #5041
Received December 2022 -
Ok, new issue! I reamed out the 5/16 bushing (which should not have been there in the first place) to 3/8 using gradually larger bits and ending with a 3/8 reamer but the hole elongated. how bad is it and does it need to be fixed?You do not have permission to view this gallery.
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From AC 43.13-1b, 7-39:
"In the event of oversized or elongated holes in structural members, reaming or drilling the hole to accept the next larger bolt size may be permissible. Care should be taken to ensure items, such as edge distance, clearance, and structural integrity are maintained. Consult the manufacturer’s structural
repair manual, the manufacturer’s engineering department, or the FAA before drilling or reaming
any bolt hole in a critical structural member."
A call to Bob would be in order. It's pretty far off.
As an idea, you could weld an extension (maybe 1/2in?) of the proper size material onto the backside, as long as the front is ok.
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I have an early 5 kit here in the shop to assist the third owner. All 4 corners were undersized and had to be reamed. The upper center bushing is 5/16” and the mount is 3/8. As you can see in the picture the alignment is way off. I will have to cut one side tube off, shorten the bushing and align it to the hole. Then re weld the tube back in place. The plans are numbered 5012 and the fuse number M57.Comment
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