A quick reply.

I'm the author of this article. Sorry for you, it's french. But very informative, argued, very detailed and didactic as possible with many sources. It took me a long time. It's worth taking the time to read. There are technical files of the mounting. I mentioned all the useful features and success criteria. When speaking about technical aspects, it's important to be as complete as possible. If not, risk of misunderstanding.

Here is an example of mounting (presented as #1 and #2 ) with translation for the readers of Bikeforums.net. This is the "technical file" (summary) with accurate measurements.

What you could (aslo) read in french in our article:

Fiche technique du montage #1 (Résumé)

In green, success. In red, to be improved.

Frame Brompton Mark 4, year 2009, with original steel rear frame (main frame # 285337)
Rear hub: Brompton Wide Range BWR, 2 sprockets, unmodified.
Type of axle of the bottom bracket: Octalink V1
Bottom bracket: Shimano BB 7700. Dimension: BSA 68 mm, lenght of the axel: 109,5 mm. Category "semi ajustable" [définition gived in french in this article]
Crankset: Shimano FC 7700
Position of the chainring: outside
Spot facing ("lamage") 1,5 mm à 2,0 mm detph on the spider
With reduction of the original chainring bolts flush to the surface of the spider)
Spacer on the BB (thickness): 1,5 mm drive side (on the right of the bike)
Space between the spider and the rear frame when folded: 1,5 mm
Chain line: [46,3 +- 0.5] mm, almost perfect. [définition of perfect chain line described in french in this article).
Q-Factor: [146,5 + - 0.5] mm
Symmetry of the Q-Factor (delta): + 5 mm (excessive value if used with clipless pedals). [définition and calcul of the symmetry mentionned also]

Conclusion of the mounting #1: mount successfully, except the delta Q-Factor.
Must add an additional ring on the BB to reduce the delta (if ring 2 mm, new delta 1 mm), therefore in the spot facing of the spider will not be useful, but + 2 mm line chain, or the solution of the washer on the axle of the right pedal (thickness of the washer on the pedal axle to 'cancel' the value of delta,= 0), or use the two schemes to avoid changing too much the chain line and to reduce too the screwed f the right pedal (as a solution, a ring of 1 mm thicker on the BB and a washer of 2 mm to achieve a new delta of +1 mm ).

What you could aslo read in french in our article:

Fiche technique du montage #2 (Résumé)

Main frame Mark 4, year 2007 , with original titanium rear frame (# main frame: ?)
Rear hub: Brompton 2-speeds hub (year 2008), 2 sprockets, unmodified.
Type of axle of the bottom bracket: Octalink V1
Bottom bracket: Shimano BB 7700. Dimension: BSA 68 mm, lenght of the axel: 109,5 mm. Category "semi ajustable" [définition gived in french in this article]
Crankset: Shimano FC 6500 Ultegra
Position of the chainring: outside
Spot facing ("lamage") NO
With reduction of the original chainring bolts (but short bolts, you can find it for some BGP, sold for fixie)
Spacer on the BB (thickness): 2,5 mm drive side (on the right of the bike)
Space between the spider and the rear frame when folded: ~1 mm (all's goo)
Chain line:: [47,7 +- 0.5] mm , almost perfect".
Q-Factor: [146,8 + - 0.5] mm
Symmetry of the Q-Factor (delta):73,9 mm (left crank to center of the tube)- 72,9 mm (right crank to center of the tube) = + 1 mm (symmetry almost perfect)

Conclusion of the mounting #2: mount successfully, including the delta Q-Factor.
Note that the delta of Q-Factor is 1 mm instead of + 5 mm. A case identical, what can explain this difference? The space between the spider and the rear frame is both 1 mm. The same range cranksets using the same axis system (FC 6500 and FC 7700) according to the logic should not play. The main frame is the cause of this difference? This is possible because no other parts can have an impact on this measure.

Do you have measure the symmetry of the Q-Factor on your Brompton?

The mounting with a new BB-7000 and almost new and complete FC 7700 costed for me 75 euros!
The mounting with a new BB-7700 and a new and complete FC-6500 costed 85 euros.

You have to search in the big old new stock or in second hand market for the crankset.
We have already made 5 mounting with a crankset and BB in Octalink V1 (we explain that bearing internal frame is better to adjust the chain line on a Brompton and even taht there is also a category entirely ajustable as certain old Campa Record BB, but hard to find now).

Picture of the FC-7700: http://farm8.staticflickr.com/7014/6...9caa8e05_o.jpg
As the Campa Record old serie, according to our taste and our knowledge, we think the best better aesthetics for the B (classical and refined).
Note that the BB-7700 is an exceptional quality and is the master piece of our mounting. But you have to mount it perfectly (follow the instructions) if not premature aging.
To save ~30 euros, you can chose a 105 or ultegra Octalink V1 BB, it's just a sealed cartridge in this case, but better than the original BB mounted till now by Brompton.


Olivier from Belgium
Abeillaud [Bromptonforum.net]
http://www.bromptonforum.net/u809