After publishing my post about Ralph’s flaws (see https://aussieonabrompton.wordpress.com/2013/06/01/ralphs-flaws/), another Alfine 11 owner has mentioned a bodge that I’d forgotten about – the wobbly seating of the chain tensioner. His fix was to modify the plastic chain tensioner but my solution was different, but first some background of the Alfine hub (& another flaw?).
Ralph was fitted with “acorn” rear axle nuts (a chrome-steel closed nut with a domed top) but I’m not keen on their “garish” look. Also, I wasn’t happy with the fact that the right hand nut sticks out & comes in contact with the front wheel spokes when Ralph is folded. The answer seemed easy; just replace it with a standard axle nut? That’s when I discovered that unlike the 10mm rear axle size for Bromptons (& probably most other hubs?), the Alfine 11 hub axle is 9.5mm. It proved rather difficult finding a nut to fit the axle & also matching the spanner size of 15mm. About this time I noticed the wobbly chain tensioner & also found that the inner axle nut (that clamps the hub to the rear frame) was equipped with a “clamping shoulder” (like a nut and washer combined). Wow! What were they thinking, to fit a shouldered nut in that position & prevent the chain tensioner from butting against the rear frame? (ie the nut shoulder was too large to go through the hole in the chain tensioner & hence the chain tensioner wobbled around on the shoulder)
I did manage to locate a 9.5mm axle nut but it had a “captured washer” as part of the nut & was unsuitable. So, out with the Dremel & I ground the top off one of the acorn nuts, to be able to use that as the inner axle nut. The shouldered nut then got used as the outer axle nut that holds the chain tensioner in place. Now the chain tensioner fits correctly & the front wheel spokes aren’t striking the rear axle nut when Ralph is folded. All ok? Well, the various axle washers are another bodge & I’ll replace them when/if I find something appropriate.
Well done if you’ve been able to keep up with all the above, & you’d probably be saying, “…but doesn’t that still leave one acorn nut on the left side of the hub?” Yes, I’d like to replace that too but it means I’d also have to grind that nut down – & also grind down the axle to shorten it to match the nut length! Sorry, I think I just might go ride the bike & leave the acorn nut in place.
Sigh… I’ve really come to appreciate the thoroughness of the original Brompton engineering & can only smile when I hear someone say, “How hard could it be, to…”
Aussie on a Brompton 
I secretly admire all of you enterprising types who fiddle with customizing your Bromptons, but do always come back to the appreciation you mention in your last lines. My B has gone more 1,000 miles since his arrival last October, and still runs exactly as he did when first picked up. That’s nearly unique in the long list of (generally quite good quality) purchases I’ve made over my lifetime so far.
Ta Brommie – & may all your customizing be successful
I’m really impressed by the detail of your investigations – I recently fitted an Alfine 11 conversion kit from a UK supplier to my brompton, and am encountering a few similar issues (like the acorn nut rubbing on the spokes, and a fair amount of resistance to backpedalling – still investigating that one) – also I have had to move the hub changing arm to be pointing a bit more upwards to avoid the rubber bellows rubbing on the chain. Out of interest, what made you orient the hub changing arm to point towards the back of the bike?
Ta for the comment Jon. I acquired Ralph locally & the original owner bought it from Fudges store in the UK. Kinetics & TillerCycles are 2 other places that build Brompton Alfine 11-speeds (I think Fudges may have stopped?) & from various bike pics I’ve seen, the orientation of the hub changing arm varies. I haven’t changed how Fudges installed the arm & think it’s not worth me trying (it seems ok & I’d prefer to get a decent look at all variations before considering it).