Robbie,
I purchased my NAS bolts from Race-Parts.com
I believe several racing web sites carry these bolts.
Bill
N67WX
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Yes but….updrilling….
Thanks guys! Still on the fence as to what to do, other than keep an eye on it.
Enlarging holes has been fraught in my experience. Are there reamers or other tools designed for this big a jump?
I agree with that assessment!! There certainly are reamers - but the smart move would be to progressively upsize the hole in steps. And be absolutely certain the reamer was 90 degrees to the hole.
I’ve done this a couple of times and it was not fun.
I’m sure others can jump in here with advice.
I think the only tricky part would be the little guide tube that gets the bolt through the cluster. I’d do that hole first, upsize the gear leg on the drill press, and then transfer the hole through the gear leg to the back of the mount.
Some ambitious person could make a guide that slides on the outside of the tube but has a piloted section to get the drill bit pointed in the right direction. A lathe and a little round piece of steel would be required.
I’d probably use something like this on that little tube:
https://www.yardstore.com/cobalt-double-margin-jobber-5-16-x-1-4-pilot-usa
For the axles, I’d upsize the first hole on the drill press and again drill through the Ti gear leg to drill the second hole.
The other thing, depending upon how tight of a fit you want, would be to measure the bolts you intend to use and get an undersize reamer.
It was my intention to stay out of this but I was intrigued by some information from my AI assistant in regards to the need for precise tolerances if upgrading the bolts from AN to NAS. Sonex doesn’t mention this in their SB so I wonder how critical this is but here’s some info as received:
“Replacing AN bolts with NAS bolts can be viable in some cases, but the fit and load path depend on proper hole size and alignment. If the holes aren’t opened (reamed or drilled) to the correct undersize for the chosen bolt class, you can lose the intended clearance or interference fit, which can undermine clamping force and structural integrity.”
I have a Corvair engine mount on an A model so the SB doesn’t apply in my case, but admittedly, I’d like to be proactive if I’m convinced there is a need to so. At this point I’m kinda with Robbie on this as to just continue to inspect these at condition.
FWIW …
Dale
3.0 Corvair/Taildragger
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Not an AI answer, but on critical holes I like to shoot for like 0.001-0.002” of clearance. This makes for a pretty snug fit. AN and NAS bolts have different tolerances. What I’ve done in the past is to measure the bolts I’m going to use and order up the appropriate undersize reamer for the final pass. I don’t really see the hole size affecting clamping force. It’s all about shear loads.
Lots of references for the bolt specs, but here are a couple I found.
AN bolts
http://www.zenithair.com/kit-data/ra/an.html
NAS bolts
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Bryan, the A model SB is there all right, albeit a little further on down the list. See SB SNX-SB-006 date 06.28.11. On a general note- the reason I would not use NAS bolts is that according to my understanding they require interference fits. When updrilling or reaming to 5/16in with mount and legs installed in the airframe, I think it would be extremely difficult to obtain any sort of interference, at least with my limited capabilities. Better to use commercial 12.9 grade, which do not require interference. And, as a matter of course and as already mentioned by others, get the threaded part of the bolt well away from any stress points.
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I’ve worked in aerospace my whole career and I’ve never heard of this. Sure you can do an interference fit but you can do that with any bolt. The key thing about the NAS bolt is that it’s stronger.
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This is the exact point I was attempting to make in my earlier post. From what I read, unless the interference fit for the NAS bolt is quite accurate then the advantage actually can become a disadvantage.
As for the 12.9 grade … they also may be considered problematic in that they are a harder bolt but also more brittle. For now I’m staying with the AN bolts as I’ve had over thirteen years of success on pavement and grass with a gross weight of 1250 lbs.
YMMV,
Dale
3.0 Corvair/Taildragger
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Let me add a few comments and pictures - now that I have completed this upgrade. My final drill bit size was 19/64”. This allowed me to use a 5/16” pilot reamer (available from Yardstore) with a 19/64” pilot. It was difficult to updrill from 1/4” to 19/64”. Titanium wants a significant pressure and a very slow drill speed. Fortunately I had some younger Sonex pilots willing to help - it just wore me out. The reamer worked fantastic and yielded a hole that required a slight tapping in of the NAS bolt - I was very happy with the final fit.
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Looks great Bill! I just found your builder’s log the other day.