Alternator Rotor Shaft Thread

[Donald H.]

I need a die to clean up the threads on a typical C2 alternator, the Delco 10dn. Through research I have determined that the shaft thread is imperial decimal 0.668 inch - 20 thread per inch.

I have searched and not been able to find this size die. I've tried 11/16 (0.6875) and 17MM (0.6693), but neither of these are correct.

I've found a number of references to the 0.668-20 including a generator/alternator part supplier that said the shaft was 0.668-20.

Anyone know of a source for somewhat odd size taps and dies?

Thanks,
Don

[David H.]

Re: Alternator Rotor Shaft Thread

I need a die to clean up the threads on a typical C2 alternator, the Delco 10dn. Through research I have determined that the shaft thread is imperial decimal 0.668 inch - 20 thread per inch.

I have searched and not been able to find this size die. I've tried 11/16 (0.6875) and 17MM (0.6693), but neither of these are correct.

I've found a number of references to the 0.668-20 including a generator/alternator part supplier that said the shaft was 0.668-20.

Anyone know of a source for somewhat odd size taps and dies?

Thanks,
Don

Don

When you say you've "tried" an 11/16 (0.6875) die, exactly what was the problem?

You indicated a need to clean up those threads. Is the problem those damaged threads are preventing die from starting?

Seems like a difference of 5 ten-thousandths should not be a deal breaker.

I've checked Murray Split Die Repair System, but can't find where they have an 11/16 20tpi split die for sale.

Dave

[Joe L.]

Re: Alternator Rotor Shaft Thread

I need a die to clean up the threads on a typical C2 alternator, the Delco 10dn. Through research I have determined that the shaft thread is imperial decimal 0.668 inch - 20 thread per inch.

I have searched and not been able to find this size die. I've tried 11/16 (0.6875) and 17MM (0.6693), but neither of these are correct.

I've found a number of references to the 0.668-20 including a generator/alternator part supplier that said the shaft was 0.668-20.

Anyone know of a source for somewhat odd size taps and dies?

Thanks,
Don

Don------


The thread size for all 1962-82 alternators is 5/8-20. It's an uncommon thread size but it is available. Try eBay,


SEE UPDATE BELOW

[Peter H.]

Re: Alternator Rotor Shaft Thread

Hello Donald. Have You Thought Of Using A Thread File. I Have Used Them To Clean Up A Damaged Thread. Usual Area Is At The Tip Of The Bolt/Shaft. Hope This Helps. Peter 🇨🇦

[Scott P.]

Re: Alternator Rotor Shaft Thread

Don, a 11/16 - 20 die is what I used to fix the alternator threads.
A company called Wholesale Tool is my source. Their part # 9163-0245 and is about $11. It is a 1.5" OD round die.
WTTool.com
If you would like Ill just send you mine and you can return it when done.
Scott Fogaley@sbcglobal.net

[Donald H.]

Re: Alternator Rotor Shaft Thread

I'm pretty confident that the thread size is .0668-20. I've found multiple sources that indicate this as the size.

From an online generator/alternator parts supplier listing for pulley nuts: 842700 - Alternator Pulley Nut, 5 Pack, for Delco and Ford Alternators, .668-20, uses 15/16 socket, 5/16 thick, For 17mm shaft


I have an 11/16"-20 die which I can make work. But I will likely also have to tap the nut to get a good fit.

I used the die to cut new threads in another old rotor shaft (17mm) and while I could get the correct alternator nut to screw on, it was difficult. If I'm unable to fine the 0.668-20 die I'll go with the 11/16"-20.

Don

[Joe L.]

Re: Alternator Rotor Shaft Thread

I'm pretty confident that the thread size is .0668-20. I've found multiple sources that indicate this as the size.

From an online generator/alternator parts supplier listing for pulley nuts: 842700 - Alternator Pulley Nut, 5 Pack, for Delco and Ford Alternators, .668-20, uses 15/16 socket, 5/16 thick, For 17mm shaft


I have an 11/16"-20 die which I can make work. But I will likely also have to tap the nut to get a good fit.

I use the die to cut new threads in another old rotor shaft (17mm) and while I could get the correct alternator nut to screw on, it was difficult. If I'm unable to fine the 0.668-20 die I'll go with the 11/16"-20.

Don

Don------

An update:

GM says that the alternator shaft thread size is 5/8-20 for all 1953-96 generators and alternators. I have found this thread size in numerous GM-sourced references. However, in this case GM is INCORRECT. I have a 5/8-20 re-tapping die and it is clearly too small to engage the alternator shaft threads.

I'm not so sure that an 11/16-20 die, which is uncommon but also available, is the correct one, either. I figure this must be a "special" thread. Why such a thread was used escapes me, though.

As far as where one could obtain the correct size die, I have no idea. If you want to take it that far, you might be able to contact a commercial alternator rebuilder and ask them if they know where to obtain such a die.

DSCN4177.jpg

[Tom L.]

Re: Alternator Rotor Shaft Thread

I went through this a few years ago when I boogered up the threads on my newly rebuilt alternator by Ken Bruno. I wasn't happy. Finding a die seemed impossible. I was able to find a thread file and with a little effort it cleaned up just fine.

[Donald H.]

Re: Alternator Rotor Shaft Thread

I did clean up the threads with an 11/16-20 die. The standard nut, which is 0.668-20, will start but will not go on without quite a bit of force. So rather than force it with a wrench, I ordered a 11/16-20 tap to re-cut the threads on the nut. This should work, I hope.

Don

[Scott P.]

Re: Alternator Rotor Shaft Thread

Guys, Post #5 tells you what, where, how much. Scott

[Donald H.]

Re: Alternator Rotor Shaft Thread

Just to close out this thread --

I did rethread the rotor shaft with the 11/16-20 die; however, the stock 0.668-20 nut would not go on by hand. I didn't what to force it with a wrench and possible destroy the threads on the rotor shaft or the nut. I ordered a 11/16-20 tap and proceeded to rethread the nut. The nut now goes on the shaft effortlessly and the threads all look good.

Thanks,

Don