lenos

OK this is pretty esoteric (isn't that part of the beauty?)

I have a 1939 Bianchi Saetta that originally was equipped with a Bianchi stamped Siamt hub and Vittoria Margherita changer. It was "updated" in about 1950 to a Sturmey archer 3 speed hub. Other than that, the brakes and rims, most of the rest of the bike is original.

I have been looking for the correct rear hub for about 3 years and finally found one albeit it is missing the original axle and wingnuts. I know the wingnuts are like unicorn horns, but I figured an axle shouldn't be too difficult. So far I'm stumped.

It appears to me that the both the front and rear axle diameters are the same relatively small size, about 8 mm, but the actual ball bearings in the rear hubs are of a larger diameter.

Does anyone out there have knowledge of these pre-war axle sizes?

Thanks,

iab

I have several sets, FB and Siamt. I'll measure them tonight.

iab

Both FB and Siamt are 8.0mm up front and 9.5mm in the back.

And lucky for you, there is a donor rear hub on ebay right now.

Vintage Very RARE Siamtrear Hub Steel Eroica Bici Epoca 20 40s Wheel Revolution | eBay

lenos

Thanks so much. I have a couple or period rear FB hubs and the recently purchased Siamt that all have the 9.5 mm. The problem is that the dropout slots are about the same or just slightly less than the axle diameters (a little uneven). I suppose that the drops could have been tweaked over the years, and could benefit from some careful filing.
The other thing that got me wondering is that the original front wing nut has a step that fits inside the front drop, and if the rear were similarly configured such an arrangement would not work with the existing rear axle diameter and dropout slot size. The most reasonable assumption is that the rear is not configured the same.

Thanks again.

Kafermann

Sorry to dredge this old thread (pun intended), but I'm working on my 1936 Bianchi Saetta Olmo and have found that the threads on the original rear wingnuts are too worn to hold the axle firmly in the dropouts. Helicoil inserts might save the day, but I need to know the exact thread specs.
Is this a true (non standard) 9,5 mm thread or a 3/8" (9,525 mm) non-metric thread.
In either case, what pitch/ TPI does it have?
I'll also need to purchase a die to chase the axle's threads, and I'm aware that some metric and BSI bicycle threads are infuratingly similar...but different. Think 9,5 mm/ 1 mm pitch versus 3/8" (9,525 mm)/ 25.4 TPI. Arrrgh!
I've rummaged through the web with a pretty fine comb, but no joy.
So, does anyone have any reliable thread data for this pre-WW2 relic?
Cheers.

iab

Italians mix metric and English. While front/rear diameters are 8.0/9.5mm, the threads are 26 tpi.

Kafermann

Oh, the joys of non- standardisation!
Seems like I'll have to ferret out the die/ inserts in some [very] old LBS. But then again, it's the thrill of the chase...
Cheers.

iab

Good luck. Those taps and dies are hens teeth. Might be best to get a chasing file.

Kafermann

Seems I've got my work (but not my threads &#128513 cut out for me. I appreciate the feedback.
Cheers.

juvela

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general background tip on working with these vintage high quality three-piece hubs:

many enthusiasts understandably wish to convert them from solid axle to hollow axle

this is often not feasible as barrels can be too narrow of inside diameter to accommodate a hollow axle

for example, FB produced a house brand hub of their own marque called CIDNEO which was only offered in a solid axle format

its barrel is too small to accept a hollow axle

mentioned only on background in case it may help someone someday...


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iab

I'd like to see pictures of your bike please.

Kafermann

This is a by-the-book restoration, so that kind of sacrilege never crossed my mind. Very good advice, however. It may save somebody a lot of grief down the line.

Kafermann

I was checking thread tables, and 3/8" 26 TPI is officialy a Cycle Engineer's Standard Thread (60 Deg). As close to the 9,5 mm thread as damn it is to swearing, given it's a 60 degree profile (and not 55 Deg). Will investigate further.

iab

I have a lot of prewar Italian hubs. I'll try to take some measurements. We have a comparator at work, but I'm rarely in the office these days. I'm supposed to go next week.