Can Threads be Saved??? Early Center Arm - Castle Nut Replacement (1 Viewer)

[Jimb074]

Early center arm assembly that appears to have lost a battle with a BFH. Was a little rusty when I picked it up and definitely seems worse after some cleanup.

Anybody have any tips or tricks that may be able to salvage these threads?
Anybody have a replacement castle nut and spacer they are willing to part with? SOR has it listed for $40 before shipping, can't stomach that idea yet. How about details regarding thread pitch and nut sizing?

 

[Malleus]

Drill the pin hole out and use one of these split dies: (of course, you need the correct size, natch)

That'll get the threads straight again. You don't need the first two for holding anything anyway. Or you shouldn't; good rule of thumb is to leave at least two threads exposed so that you can visually inspect the torque.

 

[CruisinGA]

if ^ that doesn't work, you don't really need threads where the cotter pin holes are so just gently taper bolt (removing threads where it is mangled so you can thread nut on.

 

[Jimb074]

Drill the pin hole out and use one of these split dies: (of course, you need the correct size, natch)
View attachment 3267049
That'll get the threads straight again. You don't need the first two for holding anything anyway. Or you shouldn't; good rule of thumb is to leave at least two threads exposed so that you can visually inspect the torque.

Thanks Malleus. Haven't seen or used one of these before. I think your ideas could be the way to go. As you said, need to figure out correct die to source. Any chance you know the correct thread pitch and/or nut size for this top portion of the center arm shaft?

 

[Malleus]

Not off the top of my head. Let me go outside and measure it.

 

[Malleus]

I didn't take the nut off, and there are only two threads exposed on mine, so take this for what it's worth: I measured M14 x 1.25 - Also, mine's a 1977 so that may not be the same (and mine's not drilled for a pin). Maybe @Living in the Past or @6545SWB or @Downey or @73FJ40 knows.

This is not a standard metric pitch (JIS standard is 1.5)

I'd defer to someone who knows for sure. If no one chimes in before this afternoon, I'll pull the nut off and measure it properly for you.

 

[Jimb074]

Thanks Malleus.
Please don’t take anything apart. 77 should be the later setup.
I will continue to review old posts to see if I can track down info. and parts.

 

[B y r o n]

Unlike a standard die, instead of orienting the "start side" down like for cutting new threads, you want to assemble the die below the damaged area with the "start side" up. With the die mated to the good threads you would back it off the stud which would either reform or cut threads that will line up with undamaged portion of the center shaft. The biggest problem I can see is actually finding a die with the correct threads. The cost is also pretty high for a one time use tool. You may actually be better off buying new/replacement parts.

 

[1MAC]

Buy a thread restorer file. It has different spaced teeth on each side, so it restores Thread Pitches 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 2.5, 3.0mm.
You'll end up using it a bunch if this is an example of the PO's work.
Metric thread file

 

[Malleus]

FWIW, metric threads, unlike SAE threads, are measured across the OD of the male thread; round up to the nearest even number. The measured diameter will be slightly less than the nominal thread size, due to manufacturing clearance, wear, etc. You can use a steel scale; it'll be close enough.
A thread pitch gauge is invaluable:

It doesn't have to be this one; they all work the same. You may be able to pick one up at the hardware store.

 

[middlecalf]

FWIW, metric threads, unlike SAE threads, are measured across the OD of the male thread; round up to the nearest even number.

Didn’t know this, thanks for posting. Now I just need to remember it .

 

[peesalot]

Use a dremmel to remove the threads around the top, dress the first one that will contact nut with a file so it starts properly, easy.

 

[ducktapeguy]

I would try and straighten it out as much as possible but using a punch or dowel pin through the cotter pin holes. Then use a thread repair tool to fix the threads.

Amazon product ASIN B0B64LY9MH
I've used one like this on various other projects and it works well. Then a thread file to do the final touch up.

A die will just cut new threads, that will work, but I'd try a less destructive method first.

 

[Jimb074]

Thanks to all who have contributed here, I do now have some new tools on order. Here are some progress pics. With some help from Malleus and some dial calipers, calculated that outer thread diameter @ 16mm. Thread pitch was either 1.25mm or 1.5mm. Some internet research help me to identify that 1.25 is almost impossible to source tools for and had limited parts supply. This combined with me already having a 16x1.5 die narrowed next steps to going for it. I was hesitant to use any power tools on the "thread grinding" ideas from above, so just did some hand filing to knock the high spots with the smashed threads area. There was enough of the "good" threads available to help guide the die correctly. Once I can get the correct nut, will use this as a guide to level out the top of the pin a little. Still playing squirrel and looking for that nut (and spacer) but have a few options in progress and will update again with final resolution.

So.... pre-'69 center arm top threads are M16x1.5

 

[DirtDauberGarage]

That looks great! Good job!!

 

[Nothinghead]

Did you ever find your nut?