The Stovebolt Site Forums The Shop Area The Electrical Bay Generator with 21/32 pully nut?

I'm rebuilding a 12 V generator and want to replace a buggered up pulley nut. When I mic'd the O.D. of the threaded shaft it comes up .660..21/32 in my book. McMaster Carr doesn't show one. Was this a special? 17mm?

Thanks,

Keith

Keith,

The enclosed quote was taken from an much earlier post by Denny Graham. Maybe it will shed some light on your problem.

"Again like Ken mentioned about the thread it is a special thread, actually it is a NS (National Special) 5/8”-20 thread. McMaster pn. Is 26005A148 and it will run ya $66.89. This wouldn’t be a waste if you were gonna work on a lot of these because the thread is the same from 1929 all the way up to 1954 (as far as my references go)."

Stuart

Before I replaced my generator with a 6v alternator I had to deal with a bad pulley nut. I found that a metric screwed right on and tightened up nicely. I don't recall the size. I ran it for a few months before swapping to the alternator.

I looked up 26005A148. That's the die to cut a 5/8-20 thread. I see..his suggestion was to convert to 5/8-20

17MM does equate .669 ..I measured .660
worth a try..

Thanks gents

Keith

Actually I believe it should be an 11/16-20 thread. A McMaster Carr no. 26005A155 @ $70.56 page 2520 is for a die that is national special (NS) thread. If that was a quote from me Stu, I’m not sure where I got that information. I did buy an 7/161-24 NS die for chasing the threads on the inverted flare line stuff.
Tiny, not sure what you had either, any fine thread metric nut close to that diameter would be a 1mm or 1.5mm pitch. There is a 1.25mm, which is the same pitch as our 20tpi but as far as I know that is not used in the diameters that would fit the generator shaft. The nominal shaft size is .6875” and the only metric threads that are at all even close are M16x1.00, M16x1.5 or M17x1.00, M17x1.5. The M16 or M17 fine threads are not produced in a 1.25mm pitch.
I don’t recall the thread Keith, was that Ken’s suggestion to switch to a 5/8-20 thread? I doubt if I would have suggested that unless the original thread was so bunged up that it couldn’t have been saved. I think I would have opted to get the correct die and chase the original threads.
I should mention that your measurement is an actual measurement and the if you check the shaft size you will find that it is .6875". The tops of the thread are often chopped off so the pulley will slip on with out messing up the thread so the nominal is 11/16" but your actuall will be less.

Denny Graham
Sandwich, IL

Denny Graham,

I remembered your pulley nut exercise...hope I didn't talk out of class.

https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Board=2&Number=367667&Searchpage=1&Main=50883&Words=%26quot%3Bpulley+nut%26quot%3B&topic=0&Search=true#Post367667

Stuart

Just gettin' home from helping out my buddy with his '50, 3100. Not at all Stu, you can quote anything I said, doesn't mean it was right in the first place. I'm still not sure why I would have said that unless the generator that I had on the bench had been turned down and re-threaded to 5/8"-20. I've got one out in the garage that I went out and measured after reading Keith's post this morning. And that one has the dimentions that I posted.
A lot of water's passed under the bridge and I don't really remember the conversation with Ken. Heck, I mean that was a whole year ago.
Denny Graham
Sandwich, IL

The generator shaft measures .670 by memory...the tops of the threads are .660. The nut I have has a few good threads..I've thought about chasing it with the generator shaft itself...but I'm hesitant. !7mm sound like I might luck out but they are hard to find. Places like McMAster Carr have 16 and 18 but no 17..although I find references on the internet to a 17mm. I'll wait a while and try fo find someone with a generated basket case that I can buy.

Makes me ask the question:WHY? What was the engineers problem with using a standard 5/8 thread?

Thanks,

Keith

Well count me out of the picture here, you obviously are running into problems that I’ve never faced. I don't know what you have there. I don't have a 12v generator here to compare to, only a few 6v ones and those measurements I posted earlier were what I found on the 6v generators that I have on the bench.

If you are measuring the shaft at .670" then indeed you’re measuring a 17mm diameter (.6693”). However, like I said earlier, M17x1.00 or M17x1.5 are the only thread combinations that are used as far as I know and M17 nuts would be special nuts from any supplier and not a common size. If you have access to a thread gauge (most full tap & die kits) it might help to know the pitch that you have on that armature. I just can't imagine GM using metric specs back in the day.

Don't try using a bad or good nut to chase the threads on the armature or your going to have both of them bunged up. If you read the old post I mentioned a thread file for an external thread, they're relatively inexpensive and I wouldn't be without a set.

I’m sure that Ken Warner at Classic Generator could send straighten you out on this matter and send you the proper nut for the generator that you’re working on. He has always been very helpful whenever I had a question or needed parts and is a regular contributor to the forum discussions. http://www.classicgenerator.com/
Denny Graham
Sandwich, IL

Dang I hate getting older. My rememberer doesn't work as well as it once did. Thinking more about my generator I believe what I actually did was buy a die to recut the threads so I could use a readily available nut. I don't recall the size die & it's raining right now so I'm not going to venture out to check. I believe I was thinking it may have been a metric since I couldn't find a standard nut to fit.

I'll contact them Denny-good lead..They show before and after pictures of generators...one from a 57 chevy..and it has a brand new nut on it. So they must have them..

Thanks,

Keith

That was a great lead Denny. Ken is going to send me a nut for a couple of bucks. Didn't say what it's called other than it was special.

I'm a happy boy.

Thanks again,

Keith

most delco generators and alternators use a .668x20 thread. nut is 15/16 outer diameter available from most auto electric rebuilders. hope this helps out