Turn signal stem thread difference?

[Saber]

Next up turn signal replacements. Lost two original lenses this summer due to broken housing holes. Got the new ones from AN. They only come with one nut on the inboard side

but not a problem - i can use a nut off the old stem. Wrong. The nuts on the old stem wont go on the new stem. 1/4 turn then it stops. However the nut on the new stem goes on the old stem just fine. Whats going on here?

 

[robs ss]

Do you have a set of thread gauges? Must-have for all Norton owners!

 

[L.A.B.]

The inner end thread should be 7/16" - 20 UNF and needs to be fairly consistent because the front stems screw into captive nuts in the headlamp shell so there's no separate inner nut for the front stems. The inner nuts and washers for the rear stems appear to have been overlooked by both the factory and AN. Once again, I use nylocs.

Got the new ones from AN. They only come with one nut on the inboard side

AN's pictures, unfortunately, show the nut '19' and washer '20' in the wrong positions.

The thin nut is the outboard nut, item 19:

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[Saber]

I bought these to mount in the rear. I like that they are shorter stems and will sit closer to the license plate. Why does the old inner nut not fit on the new stem? The new (thin nut) fits the same on new and old stems.

 

[L.A.B.]

Why does the old inner nut not fit on the new stem?

I don't know as I don't think the inner stem/nut thread was anything other than 7/16" UNF. Try another known 7/16" UNF nut.

 

[Mart UK]

Is the nut's thread clean?

 

[daveforty]

quick and dirty check; take the nuts off both stems and then put the stems side by side to see if the threads 'mesh'. Will give you an idea as to whether the threads are the same pitch. Or not.

 

[MichaelB]

Does the washer fit tight against the flange?
If so, insert shaft and washer outboard, nut inboard.
Source another washer if desired for inboard nut.

 

[jan nelder]

and feed it back to AN if wrong part!

 

[nonsense]

The set I bought turned out to have metric threads, if I remember correctly 11-1.25. A close-to-same thread pitch but slightly bigger diameter would explain why the new nut fits the old stem but not vise versa. Wasn’t that concerned since they were the cheapest ones I could find on eBay… I would expect AN to have better quality control!

 

[marshg246]

Next up turn signal replacements. Lost two original lenses this summer due to broken housing holes. Got the new ones from AN. They only come with one nut on the inboard side View attachment 99095but not a problem - i can use a nut off the old stem. Wrong. The nuts on the old stem wont go on the new stem. 1/4 turn then it stops. However the nut on the new stem goes on the old stem just fine. Whats going on here?

Although I prefer two nuts, the stem you have does not require two. The washer is the stop on the outer and the nut goes on the inside.

 

[Stephen Hill]

Saber wrote: " Why does the old inner nut not fit on the new stem? The new (thin nut) fits the same on new and old stems."
Sounds like the first part has been answered: the new stem is metric and the old stem is UNF.
As to the second part, which is why the skinny nut fit both the old and the new. If you have two slightly different pitch threads (similar diameter), the thin nut (or shorter bolt) is always more likely to fit because the error is compounded by the number of threads engaged.

 

[marshg246]

Some Info:

Genuine Lucas (Wassel) has no such problems. However, they are not currently making the "long thread" version. That's good for this application (rear) and unusable for front - the threaded portion not long enough. They have both long and short stem in short thread. Wassel is working the issue but no ETA. AN has both long and short stem with long threads - that's good for the front and may or may not be for the rear (interference).

The Genuine Lucas headlight shells definitely have 7/16" UNF threads. According to the AN web site, the thin nuts are 7/16" UNF.

Most likely the nut that won't screw on is 7/16" UNF cut to a tight tolerance and the stem is 7/16" UNF also cut to a tight tolerance and then chromed. I would either get some 7/16" UNF NyLock nuts to try (should have them anyway) or see if the new lights will screw into the headlight.

I would be shocked to see AN make as big a blunder and using metric threads on something that must screw into 7/16" UNF!

 

[L.A.B.]

Genuine Lucas (Wassel) has no such problems. However, they are not currently making the "long thread" version. That's good for this application (rear) and unusable for front - the threaded portion not long enough. They have both long and short stem in short thread.

The long thread is the front because it has to pass through the outer nut, washer headlamp bracket, spacer and shell captive nut.
The rear can have a short thread if the stem is long (especially for the UK and other countries that have large number plates).
There were something like five or seven variations of original Lucas thread and stem lengths (not all for Norton) not including the early stems/assemblies without the flats at the outer end and with the external lamp housing clamping nut. The pattern items are often somewhere in between and generally come in only two lengths.

 

[ILLF8ED]

My remaining stash of Lucas turn signals. The long stems used to be on the front of mine until I replaced them with short ones. Still using the long stems for the rear units. I’m going to a swapmeet in Turlock this Sunday. Think I will look for more of these.

 

[gortnipper]

When I first looked at the pic, the thread pitch looked a bit different to me. So, I copied the pic and clipped out and moved the new one to align with the other. I did not enlarge them differently. Might be just the pic though, but the pitch looks flatter on the new one.

 

[Saber]

I bought the 'long' stems for the front a few years ago. Original nuts fit fine on them. When ordering the rears I went for the short ones thinking they would match the shorter rear stems that were on the bike. I needed the whole assemblies this time. They are actually too short to fit outside the plate unless a 2nd nut is used.

I coul not get any 7/16 nut from my stash or the well stocked hardware store to go past 1/4 turn on these new stems.

I ended up using 1/2" nylock nuts as spacers for now. Theres enough nylon so they grip the threads a bit. Should be good until i can figure out something else.

 

[gortnipper]

I bought the 'long' stems for the front a few years ago. Original nuts fit fine on them. When ordering the rears I went for the short ones thinking they would match the shorter rear stems that were on the bike. I needed the whole assemblies this time. They are actually too short to fit outside the plate unless a 2nd nut is used.

I coul not get any 7/16 nut from my stash or the well stocked hardware store to go past 1/4 turn on these new stems.

I ended up using 1/2" nylock nuts as spacers for now. Theres enough nylon so they grip the threads a bit. Should be good until i can figure out something else.

7/16 UNF is 20 TPI and uses a 9.2mm drill to tap the hole.

M10 1.0 is ~25.4 TPI and uses a 9.2mm drill to tap the hole.

M10 1.25 is ~20.32 TPI and uses a 8.8mm drill to tap the hole.

You need a thread gauge and/or some metric nuts.

My bet is these are metric.

 

[marshg246]

Why not call or write AN? technical@andover-norton.co.uk

They are very helpful and it will be handled by the tech responsible for them having the product. I usually write but calling isn't overly expensive these days.

 

[Saber]

I will thanks Greg.