Hi
I have a 1941 Norton 16h with the speedo drive on the n/s front hub,
can anyone tell me what size the thread is where the drive screws into the hub, it’s a fine thread and is a touch over 18mm
any help here greatly appreciated
Smiths fittings tend...
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Conversion?
18mm = ~45/64 or .703"
19mm= .748"
11/16" = .6875"
12/16" =3/4" or .750"
I would doubt that there was anything made in metric dimensions on a 16H
I am going to guess that it is 3/4"x 26
Can anyone confirm this?
Mike
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Non-Preferred Sizes
I believe that the thread is 0.718" x 26tpi - (23/32" )
There are lots of odd sizes on these instruments and drives, probably due to their French (pre-ISO metric) origins.
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I agree with Richard, 23/32"…
I agree with Richard, 23/32"; 0.718" x 26tpi Whitworth form.
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23/32"??? Why
Does anyone have any idea as to why Norton would have chosen such an oddball thread?
Was it common to something else at the time?
Mike
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Maybe not to blame Norton
I've always thought the speedo gearbox was a proprietary item bought from Smiths. As the chronometric was initially a Jaeger design and metric, it's possible that Smiths made a small thread change to the nearest imperial measures they could figure out. Does not matter if you make 100,000 or more parts if a thread is a bit odd. Nowadays car manufacturers seems to purposely fit odd screws just to force owners to buy genuine spare parts.
Just guessing.
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Norton idiosyncrasies.
" I would doubt that there was anything made in metric dimensions on a 16H "
Hi Mike and all,
Norton were always trying to save a few bob, especially in the Depression, and from 1931 all Norton singles and most of the twins were fitted with metric wheel bearings. The SOHC racing engines used a metric timing side main bearing and imperial drive side main bearings. And also all the bore and stroke measurements are calculated in metric.
The thread pitch of metric 1mm is very close to 26 cei with just 0.016" per inch difference in length, which might be easily confused. Then there are a variety of different imperial threads on the rest of the bike, so check thoroughly, then check again !
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.....to be British Standard Brass, I believe: