Help with Crank please

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Maculatus
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Help with Crank please

Postby Maculatus » 28 May 2016, 9:01am

I've just bought a slightly used Stronglight Impact Triple crank off EBay which I am hoping to fit to my mid 90's Dawes Galaxy which I am doing up.

I believe I need a 110mm Square Taper BB to get the correct chainline, but I don't know if the crank I have bought is JIS or ISO square taper. Here is a link to a couple pics:

https://www.evernote.com/shard/s14/sh/1 ... a29f532ac8


The crank has XD2R stamped on the inside and that is the only markings.

Any insight would be most appreciated!


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Brucey
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Re: Help with Crank please

Postby Brucey » 28 May 2016, 9:08am

I think that model of crank has been produced with variations, so the best way would be to offer up a JIS axle and see how far it goes into the crank, and what chainline it gives.

cheers
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MikeF
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Re: Help with Crank please

Postby MikeF » 28 May 2016, 9:26am

I would say it's JIS taper, is made by Sugino and it looks like it has dural rings. Compare here http://www.spacycles.co.uk/m2b0s109p0/Parts-and-Accessories/Components-Gears-Chainsets. But then there are more expert users than me on this forum. :wink:
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Vorpal
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Re: Help with Crank please

Postby Vorpal » 28 May 2016, 9:55am

Brucey wrote:I think that model of crank has been produced with variations, so the best way would be to offer up a JIS axle and see how far it goes into the crank, and what chainline it gives.

cheers

But very carefully.... You don't want to damage the threads, in case they aren't a match.
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Brucey
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Re: Help with Crank please

Postby Brucey » 28 May 2016, 11:28am

just to clarify, I did mean on a loose BB, i.e. without installing it in the frame.

You can measure what the chainline will be provided you know how wide the BB shell is on the bike (usually they are 68mm wide). Just measure from the shoulder on the BB to the middle chainring (you can do this with a ruler) and add 34mm (for a standard 68mm BB shell), and that is your chainline measurement.

If you don't want to fully assemble the BB onto the cranks you can push them together by hand and (roughly) the measurement will be about 1-2mm out. [If the cranks are new (or have not been married to an axle of that type before) then it'll be up to about 2mm but if the cranks have been used with an identical axle taper previously then it'll be nearer 1mm.]

BTW the BB that you use for this purpose can be an old unit, a new unit, or a scrap unit from the LBS scrap bin, just so long as it has the same taper design as the one you intend to use it will work OK. The only complication is that not all BB units are symmetrical, so there is some potential for another error there.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Maculatus
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Re: Help with Crank please

Postby Maculatus » 28 May 2016, 11:34am

Many thanks for the detailed response.


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531colin
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Re: Help with Crank please

Postby 531colin » 28 May 2016, 7:04pm

Vorpal wrote:
Brucey wrote:I think that model of crank has been produced with variations, so the best way would be to offer up a JIS axle and see how far it goes into the crank, and what chainline it gives.

cheers

But very carefully.... You don't want to damage the threads, in case they aren't a match.


There are no threads on a BB axle.
JIS square taper BB units come with English or Italian threads to fit the unit to the frame.....a Galaxy will be an English thread.

Vorpal
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Re: Help with Crank please

Postby Vorpal » 28 May 2016, 7:23pm

531colin wrote:
Vorpal wrote:

But very carefully.... You don't want to damage the threads, in case they aren't a match.


There are no threads on a BB axle.
JIS square taper BB units come with English or Italian threads to fit the unit to the frame.....a Galaxy will be an English thread.


:oops:
of course. I was thinking of the BB and not the axle.
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reohn2
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Re: Help with Crank please

Postby reohn2 » 29 May 2016, 1:15am

99% chance of it being JIS.
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Giles Pargiter
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Re: Help with Crank please

Postby Giles Pargiter » 30 May 2016, 1:55am

Both ISO and JIS have an eight degree taper on the axle. The JIS one comes down to a slightly smaller cross section. If you have an ISO crank then fit a small shim like a pedal washer round the inside of the crank but this may not be needed. The other way round it fits together anyway.

Brucey
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Re: Help with Crank please

Postby Brucey » 30 May 2016, 7:10pm

Giles Pargiter wrote:Both ISO and JIS have an eight degree taper on the axle.


most sources say 'two degrees', not eight.

The JIS one comes down to a slightly smaller cross section.


IME, ISO spindles have a smaller size than JIS

If you have an ISO crank then fit a small shim like a pedal washer round the inside of the crank but this may not be needed. The other way round it fits together anyway.


It is a bad idea to use the wrong taper with the other type of crank, unless you really don't have any choice. Usually it is a case of about £10-15 for the correct BB, job done.

A JIS taper into an ISO crank is often a weak assembly that is prone to working loose, not running true etc. If you put an ISO spindle into a JIS crank you might stop the bolt from bottoming by using a washer on the outside but this is no consolation if you have run into the base of the taper on the spindle where you can't see it; the crank won't be secure.

Note also that whilst the taper angle is close enough between different styles of ST spindle, the design of the flats is most certainly not; depending on the type and the manufacturer the flats can have different widths and when fitting a new BB to a used crank it can be very important what type of BB was last used in the cranks; fitting a different type can cause no end of trouble if there is any wear or settling in the cranks already (and there usually is).

In any event it looks like a false economy to me, 'saving few quid' on a BB unit and risking the cranks in the process; best to get the right thing and use that.

cheers
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Giles Pargiter
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Re: Help with Crank please

Postby Giles Pargiter » 30 May 2016, 8:06pm

Of course you are quite right Brucey, don't know what I was thinking of.

Point being they both have the same angle of taper and the same spindle diameter. I have found a number of times that they do very satisfactorily swap round, with the proviso that when using the type which comes to a smaller cross section one sometimes needs a shim aka large holed washer round the inside of the crank so that it tightens properly. I find that the copper washers used to seat the injectors on a number of diesel engines ideal for this.

It is of course best to have the right parts, but if the axle length etc is right then no reason not to use it as is. I don't think it is very likely that a carbon steel spindle will be at all reshaped by even the best aluminium crank tightened on with only 1/2ton or so, must be around that with the 3/8" - 8mm bolts/nuts that are used.

No doubt worth mentioning that last time I was playing with them, SJS cycles could offer quite a selection. Cheap, but I'am still using one of them five years and over 15,000 miles later, looks as if it will keep on keepin on for sometime yet as well.

Also worth noting that Campag cranks use (I think) a 2 1/2 deg. taper - so typical Campag, they only fit Campag.