Aussie on a Brompton

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…”

What!? A Brompton with faults? Well, Ralph is a rather special Brompton, having been fitted with a Shimano Alfine 11-speed rear hub but unfortunately, it wasn’t Brompton who engineered this installation.

The concept of the multi-speed hub, fitted into a widened rear frame & using a single trigger shifter for gear changing, is great – but in practice, some engineering aspects of the fitment leave me wondering, “what were they thinking?”.

First, the mating of the Alfine hub to a Sun rim used “3-cross” spoke lacing, which had the spokes leaving the nipples at a slight angle thereby creating stress in the spokes. When I purchased Ralph there were 2 broken spokes & I immediately arranged for the wheel to be rebuilt with “2-cross” spoke lacing. I have read that Shimano recommend 3-cross lacing for Alfine hubs but I imagine Shimano were assuming a full-size wheel rim & not the small Brompton wheels? What was the wheel-builder thinking?

Something unfortunate for Ralph (principally me?) was the use of the Sun double-walled rim, with an almost flat internal profile (ie minimal “well” in the rim shape), making the fitting of new tyres a great struggle. For the present I have refrained from researching any possible alternatives; something for the future?

My next, “what were they thinking?” Is reserved for the cobbling of the chain tensioner. While the usual Brompton single-speed or 3-speed bike chain tensioner doesn’t suit the widened rear frame, the use of the Brompton derailleur (from 2 or 6-speed bikes) was an ideal/clever choice. What hasn’t been ideal is the method of relocating the jockey wheels by fitting “bike parts bin” spacers that bear up against the ends of the thin-wall tubes of the plastic derailleur arms. For Ralph the inevitable has happened & the derailleur arms have now distorted, with the jockey wheels at slight (different) angles to the chain.

Another flaw for Ralph has been an occasional dropping of the chain from the rear cog when unfolding the bike. My assumption/expectation is that the distorted derailleur & misaligned sprocket wheels are creating resistances in the chain run during unfolding & not allowing the derailleur to maintain chain tension. Owing to an imperfect chain-line deriving from the Alfine build (did I mention that Brompton didn’t engineer the Alfine build?), a loss of chain tension allows gravity to kick in & for the chain to be dragged off the rear cog when the chain moves during the unfold operation. I feel I’ve become quite adept at sensing the feel/noise of the chain dislodging & effecting a good clean remount?

Well, that’s the summary from my 6 months with Ralph; nothing that currently stops me from whizzing around on my favourite Brompton – but Ralph deserves better & a new derailleur is on order, before I turn to correctly engineering the jockey wheel mounts.