F134 Crankshaft Pulley Nut Size & Thread?

The PO substituted the wrong replacement nut to retain the pulley on the crankshaft and he dummied up the thread. He screwed it on about 3 threads with an impact gun, but it doesn't tighten the pulley. I thought I had a bad harmonic balancer until I took off the nut and found the thread damage.

A correct, new nut will not go on even one full turn. I want to chase the crankshaft threads with a thread die but don't have a thread gage or any die that size and must buy or borrow one.

Does anyone know what diameter size and thread count is on the pulley end of the crankshaft so I can buy/borrow the right size and right thread count die? Does anyone know a way to approach re-threading this so the re-threading properly hits/aligns with the undamaged existing good thread (deeper on the shaft)? I don't know if simply chasing the damaged thread with the right die will properly run me right into the good thread or not... I'd like to not make this worse.

The only size reference I could find on the internet was "standard thread" and 1-3/8 or 1-7/16 nut. Obviously the PO thought he had the right "standard thread" until it froze on the shaft so I can't do much with that. I will of course measure the thread OD and try to get a thread per inch measurement, but I don't have many good threads on the shaft, and the nut thread is recessed, so I'm hoping for some independent confirmation here.

The cj5 is a 1969, but the engine marks have all been filed off so I have no other engine ID.

Thanks.

 

I don't know offhand the thread pitch (threads per inch), but once someone informs you, a possible fix is to get a thread file. If only the first few threads are boogered, a thread file for of the correct pitch can repair them. A thread file might have as many as 8 different pitches on the various sides/ends, and they can be had for less than $20. Just make sure the one you get has the exact pitch you need.
Carefully start on the good threads further in, and work the the file around the shaft chasing the threads, working out to the damaged ones. Keep working around the shaft until they resemble an even thread pitch.
A die can then be used to further clean them up, but getting a die started on bad threads is all but impossible, so a thread file is necessary. You might not even need a die, and one of that size may be an invetment ($$).
If you can get the new nut on, at least the undamaged ones are where the nut torques up.
-Donny

 

Can anyone think of any good reason to file off an engine ID #? It occurred to me that rebuilding it might negate oversize/ undersize coding and make the the markings obsolete and "wrong"... or might help hide that the engine was stolen.

 

Thanks, Donny. I didn't know they made such an animal as a multi pitch thread file! I'll look for one tonight.

 

Might it make sense to completely grind off the "bad" end of the crankshaft to eliminate the bad threads... if I can leave enough good threads to fully engage the known good nut?

Thanks.

 

Don't know the thread pitch either, but the thread file is the right thing to use. Besides the f head in my 3B, I have one sittiing in the shop. I will try to check the tpi tomorrow

 

Do you really mean "filed?" If the block was decked by a machine shop to flatten it during a rebuild, the engine numbers may have been milled off.

 

checked my other f head this eve. 16 tpi 15/16 dia. remember the nut will only go 1 way. shoulder or shank on nut goes toward the engine, with flat side out.

 

Thanks, all. We found a multipitch file my brother forgot he had and a thread gage he thought he lost, and a yep, we got 16tpi too from the new nut and the good part of the shaft.

The shaft thread OD measured 0.990"... which feels more like 1" than 15/16" (0.9375 OD)... right? A friend thinks he can come up with a 1"-16 die for Wednesday.

I worked the multipitch file (16 facing thread) for not quite half an hour and the threads certainly visually improved, but the new nut will still not go on more than one full turn plus a little. 'Will try again Wednesday.

Thanks for all the input.

 

probably is 1 in. I measured the inside of the nut

 

Just a suggestion, I learned at work, when you get the new nut started tap on the sides with a small hammer, it helps straighten the burred threads, and reshape them. We did that a lot on anchor bolts when setting columns, they would scrape the threads going down on the base plate. Good Luck

 

I'll try that!