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Brompton Owners - Chainwheel/RH Crank

Discussion in 'Bicycle Mechanics and Repairs' started by ChrisKH, 30 Oct 2007.

  1. ChrisKH

    ChrisKH Shorts Adjustment Expert

    Location:
    Essex
    I've had problems transferring power quite recently but thought this was a gearing problem; the bike is due for a service and adjustment this week.

    I went to take over a car this morning and I ended up pedaling but going nowhere. The Right Hand Crank has sheared of from the chainwheel (or is now separate from it). I have a number of questions:-

    1) Am I right in presuming the chainwheel and crank are one piece?

    2. How easy is it to replace, or is this a bike shop repair?

    Cheers.
     
  2. Amanda P

    Amanda P The CycleChat user formerly known as Uncle Phil

    I'm not sure, but I think Brompton chainsets are a two-piece construction, with the chainring swaged onto the crank. It sounds like yours has separated at the joint (I'm assuming that as you turn the crank, the chainring stays still, but that both are still attached to the bike - right?).

    It's straightforward to replace the chainset - if you have a crank pulling tool that fits the chainset and you know what you're doing. If you've never done this before, you risk stripping threads and making things worse.

    Also, Brompton chainsets are a little bit special. Larger than most, for a start, to compensate for the small wheels, and, I think, narrower to make a neat fold. To get a direct replacement you'd have to go to a Brompton dealer, and by the time you've done that, you might as well have them do the work as well. Particularly as you say it was due for a service anyway. Your local Brompton dealer may be able to get Brompton to replace the broken bits at a discount or maybe even for nothing if it's a fairly new bike.

    I'm by no means a Brompton expert - these are impressions rather than facts. I own a Brompton but I don't have it to hand to check them. But until a Brompton anorak comes along, perhaps my ramblings will help?
     
  3. Brompton anorak here, everyone calm down.

    Listen to your Uncle Phil he is right on every count.

    Its new chainset time, possibly covered by warranty. Easy to do yourself *if you know how to do it*.

    This is an opportunity to change your gearing if you want to, Brompton chainrings are available in 3 or 4 sizes, I always recommend the smallest alloy one (the smallest chainset available has a steel ring for some bizzare reason) as Brommies are rather over geared in stock form.
     
  4. ChrisKH

    ChrisKH Shorts Adjustment Expert

    Location:
    Essex
    Thanks - just the sort of response I needed. I'll get the shop to do it then. Unlikely to be covered by warranty as this is a fairly old Brompton (L6 2003).

    Useful to know about the gearing issue - I wanted to change mine when I had work done on the back wheel and the back cog was changed but he didn't think it was possible. Maybe my version is too old to upgrade? I'll make enquiries about this because as you say, standard Brommies are over geared.
     
  5. Your bike is not too old to upgrade, the chainsets havent changed a bit since 2003.
     
  6. ChrisKH

    ChrisKH Shorts Adjustment Expert

    Location:
    Essex
    Absolutely correct - I now have a Graeme Obree style chainwheel (50T or
    52T I think the shop said) and it is making such a difference. LBS said it would as I had been running a 40T or 42T. Not even getting in top gear around town but the power increase for a Brompton is significant. Thanks for the advice Uncle Phil and Mickle. Not looking forward to that big hill on the way home though.;):tongue:

    The best thing about it was the cost. I was expecting a £100 bill for a chainwheel replacement and bike service. Final cost? £52.70, which includes the chainwheel (and round my way that's pretty good).