Happens from time to time, when you can't get the hole for the cotter pin lined up and you really want the nut tight. I'm working on the differential case and don't want to back off the nut to make the hole match ... particularly for this application.
So, maybe I buy three new differential case bolts because the old ones might be stretched. Or I file just enough from the bottom of the castle nut to go to the next slot. Or I get a steel washer and file it to the point where the hole lines up.
The conventional wisdom ?
I think I would shorten the nut. Sometimes I run a drill through to "line up" the hole, but that has a tendency to break the drill bit. Or use a lock washer and forget the cotter pin. But then, if you use a lock washer the hole may line up.
File the nut. Figure the difference from the thread pitch. Farthest you can be from lining up the hole with the castle is a quarter turn . . . a washer is miles off.
Do you want all the strength you can get? New bolts are cheap. Not every nut will be cut the same. Not every bolt will be drilled the same. A selected nut/bolt might line up better. Removing material from a nut weakens it, perhaps just a little, if you remove very little, but it does weaken it. In aircraft work there are thick and thin washers for just this purpose.
Was actually going to bring the thickness of a washer down with wet and dry emery paper so I wouldn't have to file the nut. Would also get new bolts and nuts from Langs if that does the trick.
Marc, I'm probably wrong. I usually am, but a 3/8"-24 bolt puts the threads a wee bit over .040" apart. I still maintain if holes don't line up with the castle, the most you can be off of aligning is a quarter turn. That means taking off .010" at the most. Any road, last I looked, the only flying Model T belonged to the inventor of "flubber" aka Fred MacMurray in "The Absent Minded Professor " c. 1957.
Rich: Your are not wrong. The loss by filing the nut in this case probably couldn't reduce the expected strength by more than a couple of percent, as long it is filed parallel to the original face, and as long the last guy to work on it didn't file it, too.
Well, gosh !! Anyone anal-retentive enough to file the nut to align the castle would certainly file it square !! The rest of us bozos either leave it a little slack, or over-tighten it !! LOL
I keep a selection of round shims on hand for these events. I get mine at McMaster-Carr since they're in my area for handy will-calls.
I've run into this situation a lot. What I do is use a different nut. Not all nuts have the threads starting in the same place.
Rich, I love your caveat 'I could be wrong'. I use it too, especially when talking T's, as we constantly learn new things which render previous information out of date.
You are wrong again, this time with your maths. You only need to turn the nut 1/6th of a turn to line up the castellations, unless you are using square nuts.
Sorry. I couldn't help myself.
Allan from down under.
My solution is simple and guaranteed reliable.
I buy new grade 8 bolts and nuts. Then use a torque wrench and Lok-Tite. Never a failure!!!
Brian, Thanks for the McMaster info
Allan, thanks for pointing out the error in my calculation. However, if the hole is blocked, and you give the nut a sixth of a turn, it will be blocked in the same way. So, the solution is that the most one needs to turn the nut to align castle with hole is one-twelfth of a turn, which works out to a wee bit less than .0035" to file off of a nut. Hardly worth it, eh ?