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Replacing Italian crankset

Old 10-10-17, 12:06 PM
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joedab
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Replacing Italian crankset

I recently posted preliminary efforts to repair damaged shell threads of an italian frame, and in trying to make headway, I realized the need to test ride the bike along with soliciting the help of a frame builder. To this end, I need to replace the crank which recently broke and probably also the bottom bracket. The existing bottom bracket, being a modest 70x107mm is not wide enough to accommodate a spare non-italian crank which also bottoms out on the spindle. In my perusal of available cranksets, those for sale do not seem to specify the taper standard as ISO or JIS, and a search on ebay for 'italian crankset' returns scant results. Given I haven't had to replace an italian crank before, this has me convinced I must be missing a critical spec to ensure compatibility with a given bottom bracket. Although, since I have an old non-italian crankset sufficient for testing, perhaps I simply need to find an italian-threaded bottom bracket with a wider spindle and JIS taper, though not sure if such a part exists because the listings again do specify little about the taper.

Last edited by joedab; 10-10-17 at 12:21 PM.
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Old 10-10-17, 12:14 PM
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dsbrantjr
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Identify a crankset you wish to use and then purchase the appropriate Italian-threaded bottom bracket to suit.
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Old 10-10-17, 12:16 PM
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fietsbob
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Italy used a 36mm tap.
steel frame? Damaged threads?
Sacrifices the paint, but once the old thread is spotlessly clean its possible to lay down a later of brass,

then have it re thread by a frame builder who owns The Italian Taps

Even the Japanese Companies make Italian Thread BB, and Campagnolo certainy does..






/...
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Old 10-10-17, 01:43 PM
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Italian BB's use an ISO taper... japanese standard taper is different... you must use an ISO tapered spindle for that old italian crank set.

italian frame BB's have 36mm x 24TPI threads... japanese BB's use a 1.37" x 24 TPI thread... and the French used a 35 x 1mm thread.... italian BB's will thread into a japanese frame just a thread or three, then begin binding/galling things... the japanese BB's will indeed thread into an italian frame, but will remain loose, and sometimes loose enough to cause "stripped" threads when final torqued.... the french BB's will start to thread into either of the other two types, then get tougher and tougher to turn, damaging threads along the way....

i know.... it sucks! i own two thread gauge sets... one is metric... the other is inch... i use them when any doubt is present, like a european frame.... SOME euro makers have now switched to JIS BB's... and "special orders" abound......... the french threaded frames/BB's are now getting quite rare....

and there are several other, now mostly obsolete, standards... plus a few "adapter" spindles are still floating around, mostly italian width with JIS taper....... sigh...

here.... info time... https://en.wikipedia.org/wiki/Bottom_bracket

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Old 10-10-17, 03:08 PM
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3alarmer
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Square Taper Bottom Bracket Interchangeability

ISO/J.I.S. Interchangeability

If you install an ISO crank on a J.I.S. spindle, it will sit about 4.5 mm farther out than it would on an ISO spindle of the same length.

Conversely, if you install a J.I.S. crank on an ISO spindle, it will wind up about 4.5 mm farther in than it would on a J.I.S spindle of the same length.

Theoretically, ISO cranks should only be used on ISO spindles, and J.I.S. cranks only on J.I.S. spindles.

In practice, you can very often get away with mixing these sizes, as long as you select a spindle length that gives the desired chainline.
....there are a few exceptions, like Avocet and Ofmega of a certain age, and some of the Campy stuff is confusing.
But in general you can figure out most combinations and swaps using the above link.
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Old 10-10-17, 04:48 PM
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also don't forget that for certain years campy (and ofmega) need an asymmetrical spindle.
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Old 10-10-17, 06:52 PM
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Originally Posted by joedab View Post
I recently posted preliminary efforts to repair damaged shell threads of an italian frame, and in trying to make headway, I realized the need to test ride the bike along with soliciting the help of a frame builder. To this end, I need to replace the crank which recently broke and probably also the bottom bracket. The existing bottom bracket, being a modest 70x107mm is not wide enough to accommodate a spare non-italian crank which also bottoms out on the spindle.
Ok. Trying to follow the story. You have a frame with an Italian thread bottom bracket shell, but the threads got stripped. In addition, the original crank has failed and will need to be replaced. You have found a frame builder, presumably to fix the Italian threads in the bottom bracket shell. You have another crank, but it does not work with the bottom bracket from the original, broken crank.

Am I right so far?

If so, assuming the frame builder has restored functional Italian threads in your frame's bottom bracket shell, what you need to do is set aside the bottom bracket that came with the original crank and find a different Italian thread bottom bracket that will work with the candidate replacement crank. Without knowing the make and model of your replacement candidate crank, it will be difficult to suggest any suitable bottom brackets to work with that crank.

So, what crank are you trying to use?
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