Brompton chain striking frame..

[wafter]

Seems this is happening regularly; the area of damage shown is the underside of the upper tubular section of the rear frame (what would be the seatstay on a normal bike) at its end where it meets the dropout:

This is closest to the 13T sprocket and I have my suspicions that maybe the deeper (single-speed-style) teeth on this sprocket are flinging the chain out excessively during shifting..

I've contacted Brompton and their response was to blame chain elongation (it's nowhere near its wear limit) and suggest I put something on the frame to protect it. Surely this isn't right - has anyone else experienced this? It's clearly happening regularly as I've touched it up once and there's never any corrosion...

 

[rafiki]

How many links in the chain? Have you checked that number against the Brompton chain length chart? Perhaps there are too many links.

 

[neilrichardson55]

i would say chain length, i found some plastic wrap in similar color and did that to protect parts. seems to work ok

 

[wafter]

Cheers both!

How many links in the chain? Have you checked that number against the Brompton chain length chart? Perhaps there are too many links.

It's the original chain so I assume 100 links..

i would say chain length, i found some plastic wrap in similar color and did that to protect parts. seems to work ok

Ta - although as above it should be correct. There doesn't appear to be any excessive slop.. I have protection tape and have made brass bits for various other areas of the frame, although don't fancy it's chances in that area due to the shape.

 

[rafiki]

It certainly sounds like the chain is too long. If the chain isn't stretched (I presume you have measured it with a guage?) I'd have another look at the chart and double check the number of links against your chainring and sprocket teeth numbers.. Can't do any harm.
Chain length chart

 

[neilrichardson55]

Cheers both!

It's the original chain so I assume 100 links..


Ta - although as above it should be correct. There doesn't appear to be any excessive slop.. I have protection tape and have made brass bits for various other areas of the frame, although don't fancy it's chances in that area due to the shape.

Looks like the nut is getting damage to, seems like a alignment issue, ill have alook at min tonight to see if im suffring the same

 

[wafter]

It certainly sounds like the chain is too long. If the chain isn't stretched (I presume you have measured it with a guage?) I'd have another look at the chart and double check the number of links against your chainring and sprocket teeth numbers.. Can't do any harm.
Chain length chart

As you suggest it's certainly worth checking to rule it out. It's been measured with both a Shimano 0.5% go / no go gauge as well as a steel tape; as per this post in my concise owner's thread

That said we can tell from the images in that post - both chains measured with the quicklink removed at 49.5 inches nominal, so 50 inches with the link included - which I believe is correct for the 50T chainwheel with 2/6sp rear end.

Looks like the nut is getting damage to, seems like a alignment issue, ill have alook at min tonight to see if im suffring the same

Thanks - will be interested to hear if yours is the same!

I think that might just be a bit of wax on the nut, but the chain has been abrading the inside of the dropout too:

... although that seemed somewhat transient (perhaps the result of incorrect selector adjustment in the past) and last time I checked the touched-up area looked good. Conversely a few weeks after touching up the tubular section it was absolutely bare again as pictured..


I forced the issue with Brompton and they came back essentially with "nah bruv, they all do that"; which is disappointing.. at least I took the opportunity to make them (politely) aware of how shoot I think their frame protection is from the factory. Looks like yet another area where it's left up to the owner to resolve things that should have been sorted during design / manufacture

 

[a.twiddler]

Obviously the paint's too thick! If it was thinner (if that's possible) it wouldn't make contact. Yet another thing to add to the list of things that Brompton owners have to suck up ('cos it's all about the fold, innit).

 

[ColinJ]

Yet another thing to add to the list of things that Brompton owners have to suck up ('cos it's all about the fold, innit).

Clearly, it IS all about the fold... I mean, who in their right mind would want to ride a Brompton if it didn't fold, or folded really badly!

Coincidentally, I caught a rush-hour train back from Leeds last week and a woman got on with her Brompton. She sat across the carriage from me. That's the first time that I have seen a folded Brompton close up and I was impressed by that fold!

 

[neilrichardson55]

Mine has marks not as bad but we
Do compromise on a few things being replaced a lot lolol

 

[wafter]

Mine has marks not as bad but we
Do compromise on a few things being replaced a lot lolol

Thanks - appreciate you confirming. Everything appears within its wear limit so I'm not sure that this is an issue.. I do tend to thrash the bike though, so perhaps shifting at higher wheel speeds / under load causes more chain deflection and damage..?

I guess that's another area that'll need touching up and some form of protection applying; although I suspect this won't be straightforward..

 

[Fastpedaller]

Seems this is happening regularly; the area of damage shown is the underside of the upper tubular section of the rear frame (what would be the seatstay on a normal bike) at its end where it meets the dropout:

View attachment 737800

This is closest to the 13T sprocket and I have my suspicions that maybe the deeper (single-speed-style) teeth on this sprocket are flinging the chain out excessively during shifting..

I've contacted Brompton and their response was to blame chain elongation (it's nowhere near its wear limit) and suggest I put something on the frame to protect it. Surely this isn't right - has anyone else experienced this? It's clearly happening regularly as I've touched it up once and there's never any corrosion...

Chain elongation? That's clearly just 'trying to dismiss you'. If the chain or chainring haven't been changed, then no amount of chain wear (apparent elongation) could cause a problem before the bike wouldn't function. Their answer is as daft as the one I got from Planet X when my tyres (not a Brompton) had cracked after a couple of weeks "It's the heat generated when you pedal" If only

 

[wafter]

Chain elongation? That's clearly just 'trying to dismiss you'. If the chain or chainring haven't been changed, then no amount of chain wear (apparent elongation) could cause a problem before the bike wouldn't function. Their answer is as daft as the one I got from Planet X when my tyres (not a Brompton) had cracked after a couple of weeks "It's the heat generated when you pedal" If only

Yeah, proper cop-out isn't it? To be honest given the amount of remedial / protective work required elsewhere it didn't really surprise me and like many things once they've had your money it seems that (for relatively little things at least) you're on your own..

 

[neilrichardson55]

Thanks - appreciate you confirming. Everything appears within its wear limit so I'm not sure that this is an issue.. I do tend to thrash the bike though, so perhaps shifting at higher wheel speeds / under load causes more chain deflection and damage..?

I guess that's another area that'll need touching up and some form of protection applying; although I suspect this won't be straightforward..

what about liquid rubber think layer might help and would be easy to apply

 

[wafter]

what about liquid rubber think layer might help and would be easy to apply

Cheers - tbh I think the powdercoat that's now missing was pretty tough and if it's being repeatedly slapped by the chain anything is going to get a hard time. An extended brass plate would probably be the best thing, but tbh I'm not sure I can face any more of that malarky!