cotter pin hole/castle nut not lining up

[alpinelakespilot2000]

The castle nut on one of my rear spar bolts is not lining up with the hole in the bolt when the nut is tightened anywhere within the 100-140 in-lb range for AN5 bolts. In fact, the difference b/w 100-140 in-lb is insufficient to move the castle nut even 1/2 of a slot! The plans call for regular washers, but I tried replacing one of the washers with the thin (-L) version, still no luck.

The Standard Aircraft Handbook indicates "Except in highly stressed engine parts, the nut may be overtightened to permit lining up the next slot with the cotter pin hole." (p. 151) However, AC43.13-1b says, "If the hole and nut castellation do not align, change washer or nut and try again. Exceeding the maximum recommended torque is not recommended." (p. 7-7)

Given that this is a kind-of-important rear spar bolt, I'm inclined to heed the more conservative AC43.13. So, what's the best way to address this dilemma?

Thanks.

[terrye]

I would get a bunch of AN5 bolts and castle nuts. The relationship between the start of thread and the hole/slot is not fixes. Surely one of a random lot of bolts or nuts will allow the slot to align with the cotter pin hole when torqued.

[Pat Stewart]

Is it possible to use the next longer length and then use the required washer stack to make it work.

[bhester]

Just keep trying different nuts, you'll finally find one that will match up with the hole. You'll find the same thing with the engine mount nuts.

[alpinelakespilot2000]

Thanks all. Will give some different nuts or bolts a try, but the ones on the rear spar are my last two AN5 castle nuts, so I guess I need one more Spruce order before this plane flies.

Also, a related question: the cotter pin size Van's calls out for these AN5 bolts only fold back to the center of the screw end. Are there any rules for how long the cotter pins need to be. I ask only b/c all my other cotter pins have bent back over the whole screw end and I couldn't find anything in 43.13 about them.

Thanks again though. I was really wanting to do one more Spruce order so that I could pay more shipping. Maybe Spruce will give me free shipping since this will be my (ceremonial only) last order.

[cln1owner]

Is there a mechanic on the field that might have one or two to try? If I was closer I know I have a couple.

[Wayne Gillispie]

Sand one thick washer down by hand until your hole lines up. Had to do this in several places. Apply LPS3, torque and your done. I would not waste my money on a bunch of bolts and nuts that are rare on most aircraft.

[Wayne Gillispie]

My method for cotter pins: one bend must go at least to bolt center but not past opposite side to prevent snagging.

Other bend needs to go down nut flat at least 3/4 of the way, but not touch washer. Buy longer ones and cut down as needed.

[alpinelakespilot2000]

Originally Posted by Wayne Gillispie

Apply LPS3, torque and your done.

Hi Wayne-
Why apply LPS3? I know Van's calls out for that or motor oil on the main spar bolts, some of which need to be torqued from the head on nosedraggers, but the rear spar bolts are not close tolerance and don't need to be torqued from the head. Just wondering if I missed something in the instructions.

I'll take my calipers out to the hanger and see if any of my washers are thinner than the others and/or see if I can sand one down a bit.

Thanks for the suggestions.

[GAHco]

The NAS1149F0516P should help, it is about 1/64th thick.

Link to tech pages

http://www.gen-aircraft-hardware.com...ame_HID=subcat

I hope that helps, either way you can print it for future reference.