Big nut generator nut

johnshenry · Posted: Sun Jul 29, 2007 6:23 pm Post subject: Big nut generator nut

Found my gen pulley loose at a show last weekend, decided to tighten it up today before going out on an errand. Even with the impact wrench it still wouldn't get tight. I figured it needed more shims on the outside to allow the nut to put pressure on the outer half before bottoming out.

Taking it off, I realized that the outer half was "wobbly" as the striaght sided cutout was worn..... back half too.... and the hub was kind of munged up. I know this a common wear issue and when it exists, the pulley will never stay tight.

So I rifled my parts stash and came up with what looked like a very good 25hp pulley set and an NOS (tall) hub.

With an extra shim on the outside, I got it tight. But then I started wondering about the nut and went back to the gen parts box.

I have several thicker gen nuts, like the one on my gen, where the inner snout protrudes out past the back of the outer nut surface by about 1mm. Then I have some nuts that are much thinner. I know the fan nut is also very similar.

But can someone describe the "big" 25hp nuts unique characteristics? I assume the thinner nuts are fan nuts, and after the big gen pulley nut went away, they went to the smaller (27mm I think) gen nut with smaller hub and redesigned pulley. Is the big nut just thicker than the other 36mm nut? Are there only the 2 kinds of 36mm gen (and fan) nuts?
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virtanen · Posted: Mon Jul 30, 2007 12:10 am Post subject:

All my pulley nuts have thickness of 14 mm and the center thread area is 16 mm. And I haven't had any tightening problems with them.

drscope · Posted: Mon Jul 30, 2007 8:08 pm Post subject:

I can't believe you used the impact on this.
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johnshenry · Posted: Tue Jul 31, 2007 7:36 pm Post subject:

bill may · Posted: Tue Jul 31, 2007 8:46 pm Post subject:

small slots make for big nuts. big slots have small nuts,and you can "take it to the bank"
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EverettB · Posted: Wed Sep 05, 2007 11:11 am Post subject:

Is this a 36mm generator pulley nut?

Image may have been reduced in size. Click image to view fullscreen.

It is 17mm tall.
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johnshenry · Posted: Wed Sep 05, 2007 11:20 am Post subject:

johnshenry · Posted: Sat Sep 15, 2007 7:26 pm Post subject:

Here is an original Big nut and gen pulley hub Ev. See how the barrel extends down into the hub when installed. It also extends out beyond the bottom plane of the nut also.

Its 14mm thick as measured on the side also....
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EverettB · Posted: Mon Sep 17, 2007 8:59 am Post subject:

Thank you
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Dave Haviland · Posted: Mon Sep 17, 2007 3:27 pm Post subject:

This weekend on a small zwitter shakedown cruise, the damned Big nut shook off, along with all the other parts. Luckily we were idling at a stop light. Drove it up onto the sidewalk to get out of the way and proceeded to fix the problem. Quite a crowd gathered to put in their two cents. While digging through my tool bag I realized that I didn't have my big socket. One of the by-standers thought I should use the vise-grips that were in my pile of tools. Then it came to me. The big wrench in my Hazet toolbox would work. And that it did. I may have paid a shitload for that box but it paid off. in tightening the nut, I couldn't get it tight. I think I may have lost a shim or two. We limped home and now have a 36 horse pulley in place which seems to work better. and all of those 25 horse pieces got buggered up so i guess I can throw them out. so much for correctness. but we have put 125 miles on it!

Dave

allsidius · Posted: Thu Jan 05, 2012 7:49 am Post subject:

I have a big nut generator lying around, what is the last year they were used?
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EverettB · Posted: Thu Jan 05, 2012 9:44 am Post subject:

Mid-1955
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lzamora · Posted: Sun Oct 06, 2013 10:40 am Post subject:

What is the difference between the generator pulley nut and the fan nut? Both seem identical

RareAir · Posted: Sun Oct 06, 2013 2:15 pm Post subject:

lzamora · Posted: Sun Oct 06, 2013 2:18 pm Post subject:

I pulled my fan nut from generator, measured it and it measures 14 mm just like the picture posted on this same thread with the red background.

johnshenry · Posted: Sun Oct 06, 2013 5:26 pm Post subject:

I have since learned that the common reason why the gen pulley nuts come loose is a worn opening of the outer pulley half. I think there are some pics in the "Spy Cam" thread of me fixing one with the MIG and grinding. If the pulley disc has any "play" on the hub, no matter how tight you get the nut, the disc will shift and walk the nut loose.
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Suboval · Samba Member Joined: September 15, 2003 Posts: 794

Bottoming of the generator nut to the generator shaft, due to missing or incorrect thickness shims between the nut and outside pulley, will also cause the outside pulley to be loose and crack.
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RareAir · Posted: Mon Oct 07, 2013 4:36 pm Post subject:

Chrisisw · Posted: Sat Dec 23, 2017 5:17 pm Post subject:

BulliBill · Posted: Wed Mar 27, 2019 8:58 pm Post subject: Re: Big nut generator nut

For a 25 hp pulley on a 1952 generator with the correct 36 mm generator pulley nut (see John Henry photo above), how many (and what thickness each) shims are there? All 1.5 mm thick, or a mixture of thick and thin? Thanks!

Bill
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