Retro-fitting a braze-on front mech to a folder

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horizon
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Retro-fitting a braze-on front mech to a folder

Postby horizon » 28 Feb 2020, 10:11pm

This is a bit of day-dreaming really but if anyone has any comments then please feel free.

I might want to get a Tern Link 16 (20" wheel) with a front double but they no longer import them and I cannot find one second-hand. My Tern Node 16 (24" wheel) does have the braze-on and Tern Link D8s are commonly available new and second-hand. How easy/hard would it be to retro-fit a front mech (I'm assuming you need to braze on the fitting)? The frame is alu.

More on this here:
viewtopic.php?f=18&t=107914
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher

Mike Sales
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Re: Retro-fitting a braze-on front mech to a folder

Postby Mike Sales » 28 Feb 2020, 10:20pm

horizon wrote:This is a bit of day-dreaming really but if anyone has any comments then please feel free.

I might want to get a Tern Link 16 (20" wheel) with a front double but they no longer import them and I cannot find one second-hand. My Tern Node 16 (24" wheel) does have the braze-on and Tern Link D8s are commonly available new and second-hand. How easy/hard would it be to retro-fit a front mech (I'm assuming you need to braze on the fitting)? The frame is alu.

More on this here:
viewtopic.php?f=18&t=107914


There are clamp on fittings for front mechs, designed for conventional frames in a variety of sizes. You may find it possible to fit one.

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horizon
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Re: Retro-fitting a braze-on front mech to a folder

Postby horizon » 28 Feb 2020, 10:30pm

Thanks Mike. While you were posting I found this:

https://www.ebay.com/itm/Lightweight-Al ... 0012.m1985

which might solve the problem.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher

Brucey
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Re: Retro-fitting a braze-on front mech to a folder

Postby Brucey » 28 Feb 2020, 10:38pm

The Tern Node -like many folders- has a slightly odd frame geometry which means BB is not on the seat tube centreline. This means that a standard band-on FD (even supposing the band can be made long enough) won't fit very well because the angle is wrong and the FD cage won't sit against the chainrings in the right way. It'll be worse than if the FD is meant for a completely different size of chainring.

To overcome that one method is to take a standard band-on/braze-on adaptor, and remachine it (and/or the FD itself) so that a braze-on type FD sits at a better angle.

For some bikes you don't need to make your own adaptor; third parties make them as a stock item.

Image

the above are comparable parts meant for a Dahon model. The same manufacturer may do the same kind of thing for your favoured Tern. It is even possible that the seat tube size/offset is the same between different models/manufacturers, in which case you are on easy street.

hth

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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horizon
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Re: Retro-fitting a braze-on front mech to a folder

Postby horizon » 28 Feb 2020, 11:00pm

Thanks for that Brucey. It wouldn't surprise me if the Dahon and the Tern are the same as I regularly swap over the seat post from my Tern to a Dahon Vitesse. I would be happy to explore the whole shebang with the Dahon and then swap it all over to a Tern Link if one comes up (or even keep the Dahon).

I found the clamp that you show - the problem now is just getting one from some far-flung Asian country! It looks like it comes in at around £29 which would be OK.

https://www.ebay.co.uk/itm/271963986245

Update: well I've ordered it so we shall see!
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher

rualexander
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Re: Retro-fitting a braze-on front mech to a folder

Postby rualexander » 29 Feb 2020, 12:29am

horizon wrote:Thanks Mike. While you were posting I found this:

https://www.ebay.com/itm/Lightweight-Al ... 0012.m1985

which might solve the problem.


I put one of these on my Brompton last year, now have a triple chainring set up working fine.

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horizon
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Re: Retro-fitting a braze-on front mech to a folder

Postby horizon » 6 Apr 2020, 10:23am

horizon wrote:
I found the clamp that you show - the problem now is just getting one from some far-flung Asian country! It looks like it comes in at around £29 which would be OK.

https://www.ebay.co.uk/itm/271963986245

Update: well I've ordered it so we shall see!


Well it's arrived! Given the circumstances and the fact that it was posted from Hong Kong I think that's quite amazing. It is as described and looks like it will do the job - now just to find the time to do it.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher

rotavator
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Re: Retro-fitting a braze-on front mech to a folder

Postby rotavator » 6 Apr 2020, 7:16pm

rualexander wrote:
horizon wrote:Thanks Mike. While you were posting I found this:

https://www.ebay.com/itm/Lightweight-Al ... 0012.m1985

which might solve the problem.


I put one of these on my Brompton last year, now have a triple chainring set up working fine.

That sounds interesting and I might try this myself so can you give some more information e.g. what size chainrings, what chain tensioner or RD used please?

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Re: Retro-fitting a braze-on front mech to a folder

Postby rualexander » 10 May 2020, 8:06pm

rotavator wrote:
rualexander wrote:
horizon wrote:Thanks Mike. While you were posting I found this:

https://www.ebay.com/itm/Lightweight-Al ... 0012.m1985

which might solve the problem.


I put one of these on my Brompton last year, now have a triple chainring set up working fine.

That sounds interesting and I might try this myself so can you give some more information e.g. what size chainrings, what chain tensioner or RD used please?


42-34-26 chainrings.
Standard Brompton tensioner.
Shimano Claris front derailleur https://www.sjscycles.co.uk/derailleurs ... r-brazeon/

I have subsequently also upgraded to a triple rear sprocket on the BWR rear hub using https://www.sjscycles.co.uk/sprockets/m ... 12-14-17t/

So my gear inches range is now 16"-88".

drossall
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Re: Retro-fitting a braze-on front mech to a folder

Postby drossall » 10 May 2020, 11:45pm

This thread is useless without pictures...

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Patrickpioneer
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Re: Retro-fitting a braze-on front mech to a folder

Postby Patrickpioneer » 12 May 2020, 4:02pm

drossall wrote:This thread is useless without pictures...


have a look at this
viewtopic.php?f=5&t=117916&hilit=brompton+front+mech

2_i
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Re: Retro-fitting a braze-on front mech to a folder

Postby 2_i » 12 May 2020, 4:15pm

Brucey wrote:the above are comparable parts meant for a Dahon model. The same manufacturer may do the same kind of thing for your favoured Tern. It is even possible that the seat tube size/offset is the same between different models/manufacturers, in which case you are on easy street.


The particular pictured adapter is actually mediocre, because the thinned extended alu finger, holding the derailleur, bends over time. Other adapters, with shorter and thicker fingers, and usually cheaper, work well better.

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horizon
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Re: Retro-fitting a braze-on front mech to a folder

Postby horizon » 12 May 2020, 5:29pm

2_i wrote:
Brucey wrote:the above are comparable parts meant for a Dahon model. The same manufacturer may do the same kind of thing for your favoured Tern. It is even possible that the seat tube size/offset is the same between different models/manufacturers, in which case you are on easy street.


The particular pictured adapter is actually mediocre, because the thinned extended alu finger, holding the derailleur, bends over time. Other adapters, with shorter and thicker fingers, and usually cheaper, work well better.


This is the only one I found. I think there is also an issue with the "offsetness" of the tubing which Brucey might have alluded to above and which might require a long finger.

The one I bought wasn't cheap (but looks OK) but if you can point to any others I would be interested.
When the pestilence strikes from the East, go far and breathe the cold air deeply. Ignore the sage, stay not indoors. Ho Ri Zon 12th Century Chinese philosopher

2_i
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Joined: 25 Feb 2020, 3:12am

Re: Retro-fitting a braze-on front mech to a folder

Postby 2_i » 12 May 2020, 6:23pm

horizon wrote:This is the only one I found. I think there is also an issue with the "offsetness" of the tubing which Brucey might have alluded to above and which might require a long finger.

The one I bought wasn't cheap (but looks OK) but if you can point to any others I would be interested.


The angle is indeed an issue and adapters marketed for different brands can yield a slightly angle and range of placement that compensates for the angle. For fine adjustments you need this asymmetric washer:

https://www.amazon.co.uk/Sram-FDRS0002-Adjustment-Derailleur-11-7615-011-000/dp/B003RLK1WQ

The sturdier adapters with nominally the same functionality as the one you got include these:

https://www.aliexpress.com/item/10000022927644.html

https://www.ebay.co.uk/itm/Foldable-Bike-Front-Derailleur-Adapter-Clamp-Aluminum-Alloy-Conversion-UK/233567605023

However, you need to use a flat washer with these on the bolt side, rather than a rounded one that comes with the derailleur.