I'm going to get in trouble for this... but I think it's worth it :)

[Deleted member 1258]

Went out for a first ride on the bike, planning on heading to the coast and back for a nice flat 40 miler.....

Got about two miles from home and chain snapped

Wasn't even putting in *that* much power when it happend, though it was up a hill. Is this more common with fixed gear than with freewheel bikes? Is it perhaps a sign that I need to get the chain line better than it currently is perhaps? It's the only chain I've ever broken, it was quite a shock when it went!

View attachment 356816 View attachment 356817

I was planning on ordering some new tyres for the bike anyway so I guess I'll add a new chain to that order.

Unfortunately that drive side crank does also rub against the chain stay under power. Can't decide whether to crimp the chain stay a little or to try and find a new axle... the difficulty there will be that the seller said he couldn't shift the BB fixed cup (a problem I've encountered on a few other bikes).

That looks like a simple chain failure, looking at your pictures your chainline looks OK. I think you need a longer bottom bracket axle though, trouble is a longer axle will mess up your chain line and you'll have to sort that out once the longer axle is fitted.


https://www.sjscycles.co.uk/cottered-traditional-axle/


http://www.starcyclespares.co.uk/no...ed-bottom-bracket-cycle-crank-axle-2730-p.asp

 

[ChrisEyles]

Thanks @dave r that's good to hear. Is chain failure like this more common on a fixed gear bike, since I've never broken a chain in tens of thousands of miles?

I've had a look at the chain line using a straight edge (length of wood) laid along the chain ring and it looks like the sprocket is set about 3mm-5mm out of the plane of the chain ring. I'd have thought this should be close enough to work OK.

If it's only the crank/chainstay interface causing problems, has anyone tried putting a crimp in the tube with a vice? Seems like it should work but I'd be much happier doing this if I knew others had succeeded without compromising the frame strength.

Otherwise I guess I'll have to get a new BB spindle (and hope a new one will be compatible with the fixed cup since I can't remove it), and use some spacers to get the rear sprocket into a good position for the chain line.

 

[Deleted member 1258]

Chain failure is rare, the only time I broke a fixed chain was back in the 1980's, and the chain was badly worn, and the same when I broke a chain on a geared bike, that was a long time ago and the chain was very worn. If the sprocket is a little outboard of the chainring that might make it easier if you decide to change the bottom bracket axle.

 

[Lonestar]

Chain failure is rare, the only time I broke a fixed chain was back in the 1980's, and the chain was badly worn, and the same when I broke a chain on a geared bike, that was a long time ago and the chain was very worn. If the sprocket is a little outboard of the chainring that might make it easier if you decide to change the bottom bracket axle.

Blimey...It hasn't been for me...Even had one go at Canning Town last year.Managed to get back and realised how bad it was.I was actually lucky to get back on that one as it was hanging by a thread.Over the years I've had a few chain incidents and with the pedal crank incident last year nothing seems impossible to me.I'm very careful how I put chains together now,also.

Im riding a 50/17 or 50/15 on two different fixies so that probably doesn't help.

 

[Deleted member 1258]

Blimey...It hasn't been for me...Even had one go at Canning Town last year.Managed to get back and realised how bad it was.I was actually lucky to get back on that one as it was hanging by a thread.Over the years I've had a few chain incidents and with the pedal crank incident last year nothing seems impossible to me.I'm very careful how I put chains together now,also.

Im riding a 50/17 or 50/15 on two different fixies so that probably doesn't help.

Back in those days I would tend to run a chain to destruction, these days I change them regularly, I rarely have a chain on a bike more than twelve months, there are plenty of cheap fixed chains available and they can be treated almost as disposable. I also run a lower gear and spin more, my current fixed has a 44x18 with a 165 crank.

 

[ChrisEyles]

Wow @Lonestar 50/15 is a monster gear!

The cranks on this bike seem fairly long - haven't measured but I guess 170-175.

 

[Alan O]

...has anyone tried putting a crimp in the tube with a vice? Seems like it should work but I'd be much happier doing this if I knew others had succeeded without compromising the frame strength.

I really would never do anything like that - I really would expect it to weaken the frame, and perhaps even crack it.

And to be honest, it's a bodge to get round doing the job properly - you know that a longer axle is the proper solution.

Alan

 

[ChrisEyles]

@Alan O yeah, I know a longer axle is the way forward. I've seen people put a larger crimp in the chain stays to fit bigger chain rings on single speed bikes before and was curious about having a go at this myself... but for the sake of a couple of quid and an hour or so's work I might as well do it properly. I'm hoping to get the BB spindle out to measure it up for a replacement this weekend if I get the chance.

Some people will do anything to get out of working with cottered cranks, eh?

 

[Alan O]

@Alan OSome people will do anything to get out of working with cottered cranks, eh?

That's understandable - but it does give you the chance to use a ****ing big hammer

 

[ChrisEyles]

I've never had much luck with the hammer on the bikes I've worked on. I've only ever got them out using a big-ass bench vice and a socket to press the pins out. They don't half make a bang when they come out sometimes!

These ones should hopefully be OK, since the seller had the cranks off fairly recently to re-grease the BB.

 

[biggs682]

@ChrisEyles ouch re chain i hope you didnt damage yourself ?

Chain line needs to be as good as poss , re swapping crank as long as one cup comes out its doable just

have you tried using a 13 or 14mm bolt on stuck bottom brackets cup i have used it twice with success

still looks good though

 

[ChrisEyles]

I've got a good bruise on my knee where it hit the handlebars, but no harm done fortunately. The chain didn't jam so the rear wheel free-wheeled rather than locking up which was a plus.

I've re-greased the BB on a few bikes without removing the fixed cup, so should be fine swapping a new spindle in to get the chain line spot on and a bit more clearance between the cranks and the frame. Just need to measure it up and hope I can find one the right length.

Never tried the 14mm bolt method, but I'll look this up. I'm assuming/hoping that a new spindle will be perfectly compatible with the current cups, but if I do need to fit new cups then that might come in handy!

 

[mjr]

Thanks @dave r that's good to hear. Is chain failure like this more common on a fixed gear bike, since I've never broken a chain in tens of thousands of miles?

I think it's pretty rare whatever the bike, but you can get away with running a more worn chain on SS/FG/HG if you keep retensioning the chain as there's only one sprocket to wear evenly matching the chain IYSWIM. The only chain I've known fail was during a fluffed low-cadence rear shift on a derailleur bike... but I've only ridden SS and HG, not fixed.

I've had a look at the chain line using a straight edge (length of wood) laid along the chain ring and it looks like the sprocket is set about 3mm-5mm out of the plane of the chain ring. I'd have thought this should be close enough to work OK.

Close enough, but straighter is better if you can.

Otherwise I guess I'll have to get a new BB spindle (and hope a new one will be compatible with the fixed cup since I can't remove it),

I'd be very surprised if the BB spindle isn't one of the common sizes. Take it out, look for markings (NECO if you're lucky) and measure it.

 

[biggs682]

I've got a good bruise on my knee where it hit the handlebars, but no harm done fortunately. The chain didn't jam so the rear wheel free-wheeled rather than locking up which was a plus.

I've re-greased the BB on a few bikes without removing the fixed cup, so should be fine swapping a new spindle in to get the chain line spot on and a bit more clearance between the cranks and the frame. Just need to measure it up and hope I can find one the right length.

Never tried the 14mm bolt method, but I'll look this up. I'm assuming/hoping that a new spindle will be perfectly compatible with the current cups, but if I do need to fit new cups then that might come in handy!

A longer spindle and then get the rear wheel dished and spaced to get the chain line near as

glad no major injuries

 

[ChrisEyles]

As far as I'm able to accurately measure it, the BB spindle dimensions are

Width between cones = 54.5mm
Cone to non-drive side crank notch = 19mm
Cone to drive side crank notch = 22mm

The closest match I can find (on SJS cycles, have looked elsewhere too though) is:

Width between cones 51mm
Cone to non-drive side crank notch = 22mm
Cone to drive side crank notch = 32mm

This would mean the adjustable cup has to be 3.5mm further into the BB shell to fit the new spindle. This would be just about OK, but I'd worry there wouldn't be quite enough thread to get the lock-ring on good and tight.... that is *IF* my measurements are all accurate!

The non-drive side crank would then end up in the same place (fine) and the drive side crank would be moved away from the frame by 10mm (a bit too much, but also OK since I could adjust the spacers either side of the sprocket, or re-dish the wheel).

Does that sound like a close enough match do you think?

PS - @mjr the current spindle has the letter "P" and the number "27" stamped on it. Any ideas what this means for the width between the cones (I couldn't find this info online yet)?