Odd size Fork Thread & Diameter; vintage

[Phil Fink]

I have a couple of vintage pre-balloon motobike forks that look like 24 tpi, but a 1" die just barely won't fit/start on those; [it can be turned by hand (no tool holder/handle) on a regular set of 1950's or so forks]. The diameter looks like 1-1/32" or 1-1/16" or maybe 26 mm or 27 mm, in metric. Was this common for that era? Is there an adjustable diameter die that can be adjusted up from 1" for oversize threads? Or is it possible that both forks were stretched over the years, by overtightening the stem at the threads? One had a cap and no threaded cone; the other has neither of those. I don't think that I can take a picture that would show the 1/32" size difference.

 

[RustyGold]

To find out what you have, you need to get the outside diameter measurement with some calipers/micrometers/etc...and then get a thread gauge set to check the tpi. I'm sure harbor freight (ack,spit) has a thread gauge set for $5 or less.

If it is some weird slightly oversized thread with the same pitch (tpi), then most die have a split with a screw that can be tightened down to slightly oversize it. I think your going to find that they are a different pitch, however.

Jason

 

[Phil Fink]

measurement with some calipers/micrometers

I guess its time for that new battery in my digital calipers.

find that they are a different pitch

The threads look like 24 tpi when I put another fork's threads next to them. Well, sometimes I use a 10-24 screw, but although the count (24) is right, the shape (size, depth) is not the same, making a visual comparison seem off when it might even be the same.
I do have another 1920's truss fork (Westfield) that was 1"-26.
Maybe the others are teens or twenties also, could be why the truss forks were such a bargain.

 

[RustyGold]

The threads look like 24 tpi when I put another fork's threads next to them. Well, sometimes I use a 10-24 screw, but although the count (24) is right, the shape (size, depth) is not the same, making a visual comparison seem off when it might even be the same

A 10-24 screw would be an accurate gauge. Regardless of diameter, the threads are exactly the same on all 60° threads of a given tpi...10-24, 1/4"-24, 5"-24. So, if the 10-24 threads don't perfectly sync...not 24tpi.

If metric, a M26 x 1.0mm thread would look very much like a slightly oversized 1"-24 (1.0mm is 25.4tpi). But, if it is old and American...I suspect it is some odd size like the 1"-26 you mentioned.

Jason

 

[Phil Fink]

For a brown-tone Mead Ranger project:

 

[Phil Fink]

For another double bar drop frame project (girls cut-down?):

 

[scrumblero]

BSW (Whitworth)?

 

[Bicycle808]

Measure the OD of the steerer tube, like others said, but take several measurements from different spots along the circumference. I suspect that they may be ovalized, like you'd said...

 

[RustyGold]

BSW (Whitworth)?

Anything is possible, but not probable. Whitworth threads are rounded at the peaks, not flat like UN or metric threads...also 55degree, not really noticeable by the naked eye...but, if you got a thread gauge and the tpi was dead on but the gauge would not sit all the way into the threads (mesh)...could be whitworth.

Having owned a couple english motorcycles in my younger days...I completely detest all things whitworth .

Jason

 

[Bicycle808]

¨Whitworth-less.¨ It´s a shame b/c Brits made a lot of cool machines, but the Whitworth tools and hardware are such a PITA, it kinda ruins the experience for me.

 

[scrumblero]

Anything is possible, but not probable. Whitworth threads are rounded at the peaks, not flat like UN or metric threads...also 55degree, not really noticeable by the naked eye...but, if you got a thread gauge and the tpi was dead on but the gauge would not sit all the way into the threads (mesh)...could be whitworth.

Having owned a couple english motorcycles in my younger days...I completely detest all things whitworth .

Jason

Only thing that made me think of it is my Rudge.. had to re-machine the old headset cause it was BSW and couldn't find another that cost less than the bike.

 

[RustyGold]

Both my BSA and Triumph came with a wide variety of Whitworth, metric, and standard fasteners...forced into whatever hole they 'almost' fit. Nightmare.

Jason

 

[Bicycle808]

Both my BSA and Triumph came with a wide variety of Whitworth, metric, and standard fasteners...forced into whatever hole they 'almost' fit. Nightmare.

Jason

@Bicycle808 does NOT like this.

 

[Phil Fink]

Was this common

I believe it must be M26-1mm, then.
I can get a 1"-24tpi nut or cone to 'start' on some 1"-26tpi forks, and vice-versa. The same should apply to the 1"-24tpi die tool, (and maybe even for 55 BWS versus 60 degrees).

Upon further research, I believe that the forks may have been made in East Germany (M26 headsets), and then threaded in China (M26 die tools).

 

[Bicycle808]

I believe it must be M26-1mm, then.
I can get a 1"-24tpi nut or cone to 'start' on some 1"-26tpi forks, and vice-versa. The same should apply to the 1"-24tpi die tool, (and maybe even for 55 BWS versus 60 degrees).

Upon further research, I believe that the forks may have been made in East Germany (M26 headsets), and then threaded in China (M26 die tools).

Weird. Any idea when the forks were made, and for which bikes? I´d read about the German and Austrian vintage bikes; if I´ve ever seen one myself, i never knew it b/c i kept the stock headset, i guess. (Old Austrian-built lightweight... i thought it was 1¨?) Here´s some interesting stuff, if you sprechen die deutsche.
http://ddr-fahrradwiki.de/Steuersätze
Not sure where the Chinese threading would come in, though...

 

[RustyGold]

Sheldon's site has a table of threaded headset sizes...
https://www.sheldonbrown.com/headsets.html
It shows that the French, East Germans, Austrians, and even Raleigh played around with different thread diameters/pitches.

Jason

 

[Phil Fink]

Weird

Sheldon

French

Raleigh

It's funny that I plan to use the fork on a Mead Ranger project, and that a proud English(?) guy said he had never heard of such American bike.
I have a French headset, (won't fit anything), and then got a Raleigh headset to adapt on a 26tpi Westfield fork. I have to watch my sarcasm, I do have a M26 die tool on-order from China ($10-only source I found), and I have seen an M26 headset for sale from Germany (only source I found) in an ad loosely translated online into English (they don't ship to Germany!?).

So the fork may just be Austrian, or one of various teens and twenties makes lost to history; if the M26 die tool fits, may get a M26 1mm headset.

 

[Bicycle808]

??