Yoke stem thread problem

fiatfan

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So I´ve managed to mix older and later yokes on my build, which seems to work fine. I now have an earlier (Atlas) lower yoke with 26 TPI threads on the stem, and a later top yoke from an early Commando. These fit together, nothing wrong, but have I got it right when assuming (after reading a lot) that there´s only two different threads on the stem of these yokes, 26 on the pre-Commando and 28 TPI on the Commando? I have two top nuts with threads I can see nothing wrong with, both 26 TPI, flawless threads on the stem, and even when tightening the nut full and back it of just a little bit, it´s really loose on the stem. So much that I´m shure it will pull the threads if I tighten down the top yoke to the correct torque. It´s the same with both nuts.
I used a digital vernier and measured the top of the threads in the nut, and the bottom of the threads on the stem, and the difference is 0,33 mm which is something like 0,014".
I´m ordering a new top nut this weekend just as a test, don´t understand this....
 

bsaboss

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Earlier Nortons had a larger diameter steering stem, so perhaps you've got a 26TPI nut from an early yoke.
 
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Earlier Nortons had a larger diameter steering stem, so perhaps you've got a 26TPI nut from an early yoke.
Earlier norton???? any specifics...

13/16x28 series 1/early commando
I have both the tap and die for this set and needed and used them.
or
13/16"x26 featherbed 7-3/8" triple trees
completely unable to source the tap and die in usa. Only seen them in UK...mail order

7" slimline??? wideline???
 

bsaboss

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The earlier Nortons I was referring are pre-featherbed ones. From the RGM parts listing on the steering stem nut for the earlier type "FITS THE STEERING STEM BELOW THE TOP YOKE ON PRE FEATHERBEDS. THE EARLIER STEMS THAT THIS NUT FITS ARE NOMINALLY 11/8" DIAMETER COMPARED TO 1" USED ON THE FEATHERBEDS." The nut looks pretty much the same but would obviously be a very loose fit on a later stem (as described by the OP).
 
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I think the RGM description is off a bit. The 1" featherbed dimension is not the stem but instead the 1" goes into the triple tree (bearing end is 25mm)
I'm not going to take my 52 Model 7 apart to find out the stem thread- sorry
 
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The early Commando nut will have a series of circles on one of the flats of the hex to indicate it is a UNF thread. Because the hex is so thin on this particular part you may only see a part of a circle. This was standard practice to distinguish the UNF threads from the various other threads such as CEI and BSF etc.
 
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