rear hub mystery parts

hello Forum. hope you are all good.

I have a mystery regarding rear hub parts. perhaps some kind person may be able to enlighten me on this.

regarding rear wheel assembly.

I have 2 cush drive hubs, visually identical. call them A and B
dismantled both hubs with the intention of test fitting one hub without rim.

Findings::
group 20 Rear Wheel item 31 (NM18234) the spacer behind the left hand threaded nut

Hub A spacer length .812" . bore parrallel .677"( this is whats on the bike and fits)
Hub B spacer length .894" . bore has 2 diameters .673" and .576"(this is the hub only for test fitting purposes)

the .576" dia bore of spacer B is on the timing side of the bike. this cannot be assembled the wrong way around. Therefore a top hat bush NM13270 cannot be used with hub B spacer NM18234.
All parts appear original
there appears to be 2 different length spacers for cush drive hubs. driving me nuts

is this issue related to those threads where it was advised that recourse to a stout block of wood as an aid to spreading the swingarm was recommended. if the long spacer was used then the assembly is 82 thou too long for my swingarm.
all help very much appreciated
very best wishes to all
Bradley

I suspect you just need to spread the swing arm a little. I had to do that so I could get #4 in.

Hello Snorton 74
thanks for your reply
thats what I dont want to do, spread things out using force.

the main point is that there seems to be 2 versions of item 31. one is 82 thou longer than the other. the bores are also different. 2 completly different spacers . cant use top hat bush NM13270 with the long spacer either.

as I said the short spacer fits and came off the bike and is no problem. I dont think I would like to open my swingarm 80 thou by using force.iI would bet that the factory design never required the swing arm to be forcefully spread to fit rear wheel.

i would simply like to know why there are 2 versions of NM18234 item 31. there nust be an explanation.
thanks again
Bradley

You don't say what year and model of Commando this is for ?

I have disassembled lots of cush drive hubs and earlier ones to, I have never come across (B) and see no reason why it would have 2 different internal diameters, I would replace it with another (A)

On my 1974 Norton Mark IIA the spacer that you are discussing has a length of .811 inches. There is a lip on the inboard end of the spacer that acts as a belt seal guide. Mine is step bored with a larger hole on the outboard end. I suppose that my spacer with the step bore is an improvement over the earlier ones.

When looking at the early 1968-70 Norton parts book, it appears as though that spacer has the same part number continuing throughout all of the years 1968-1974.

I woke up last night and realized I made a mistake on my last post! The spacer that I described does not have a stepped bore at all. I don't know what I was thinking! However, when thinking about the spacer that you described for Hub B it was probably a custom fabricated spacer made so that the speedometer drive could be eliminated.

PeterJoe said:

However, when thinking about the spacer that you described for Hub B it was probably a custom fabricated spacer made so that the speedometer drive could be eliminated.

Click to expand...

madass140 said:

I have disassembled lots of cush drive hubs and earlier ones to, I have never come across (B) and see no reason why it would have 2 different internal diameters, I would replace it with another (A)

Click to expand...

Hello Forum. thanks very much for all posts.

the hub with the nystery spacer was purchased as a spare hub . I have no idea of the history or year of production of this hub.

if people have dismantled lots of these, there should be evidence of 2 types. there is not.

Therefore I think PeterJoe suggestion makes good sense.

A final query, if I may:: does the specific model matter that much. are bolt up and cush interchangable with each other and across the 750/850 swingarms.

Thanks again all
Bradley

"A final query, if I may:: does the specific model matter that much. are bolt up and cush interchangable with each other and across the 750/850 swingarms."
If you are referring to the spacer only, I'm fairly certain its the same item many years , boltup included. I dont know what the part numbers say, if they are different it could be an updated part number not necessarily a new part.

Interesting. At the expense of sounding stupid, what about us who have powder coated the swing arm and brake cover plate and have about 1/4" of extra coating that was never there before? I knew that my long spacer was tight, but it always seemed tight, I never thought about it spreading the arms after I powder coated until it was brought to my attention by the single piece axle. But I never had to lever anything in place. Is this spreading of the swing arm something to worry about or something that's just not absolutely correct?

Dave
69S

Might consider trimming the strange #31 spacer so parts seat well and maybe also the speedo drive spacer as its very tough to spread swing arm much at all and should not be a banging wearing hassle just to change tires.

It's never been hard to get things together, even the way it is now with the powder coat. Just a hand operation.

Yeah, I trim that spacer and then the next guy that finds it says " what is this part?" Just like Bradley. I could just remove the powder coat from the necessary parts and repaint with regular paint. I find the dremel with a little wheel removes the powder easy but it leaves a lump at the transition, but so what.

Dave
69S