2nd crank failure (same place) - my fault?

[alvintc]

The odd thing is, both my failures are in a different place to every other one I see... All the listed failures are on the "spider" where mine is on the crank arm (both times)

 

[C R]

The odd thing is, both my failures are in a different place to every other one I see... All the listed failures are on the "spider" where mine is on the crank arm (both times)

But I think it is attributable to the bonding of the two parts failing over time.

 

[SkipdiverJohn]

Modern bike engineering is really really shite. You very rarely ever get any problems with square taper cranks, and failures on cottered ones are virtually unknown.

 

[rogerzilla]

Square taper is good but it does have a few issues:

1. Chainline is inexact due to sloppy tolerances and no.2 below
2. The interface wears if the crank is frequently removed and refitted
3. Really big heavy riders have found that the crank can crack at the square hole, even though it is really 8-sided to reduce the risk of this
4. The cranks, especially the left one, have a tendency to slide down the taper in use

In practice all of these are avoidable and the more modern options have similar or worse defects.

 

[davidphilips]

Modern bike engineering is really really shite. You very rarely ever get any problems with square taper cranks, and failures on cottered ones are virtually unknown.

Stopped using vintage bikes but tbh seldom had any problems with vintage bikes and have cycled both on club runs on bikes over 70 years old that i just know could still be ok in another 70 years if looked after, yet some of the new bikes that have inbuilt flaws in there design that lead to frame failures if you as much as carry the bike and let the handlebars swing around is madness. Sorry Cervelo owners?

View: https://www.youtube.com/watch?v=yajCXeNTbqk

 

[pawl]

Modern bike engineering is really really shite. You very rarely ever get any problems with square taper cranks, and failures on cottered ones are virtually unknown.

Until you started bashing the cotter pin with a lump hammer to remove the b¥_^ things.If you didn’t damage the crank god knows what damage was caused to the bottom bracket unless it was supported when hitting the cotter pin🥵🥵🥵

 

[rogerzilla]

Stopped using vintage bikes but tbh seldom had any problems with vintage bikes and have cycled both on club runs on bikes over 70 years old that i just know could still be ok in another 70 years if looked after, yet some of the new bikes that have inbuilt flaws in there design that lead to frame failures if you as much as carry the bike and let the handlebars swing around is madness. Sorry Cervelo owners?

View: https://www.youtube.com/watch?v=yajCXeNTbqk

To be fair, it's not that different from your bars swinging round and putting a massive dent in the top tube on a bike without a rear brake cable to damp/limit the movement.

 

[ColinJ]

Modern bike engineering is really really shite. You very rarely ever get any problems with square taper cranks...

This is one of mine that I spotted before it had the chance to break!

I didn't take a photo of the one that actually DID break...

And several friends have broken square taper cranks too. Given that I don't actually have hundreds of friends and haven't cycled hundreds of thousands of kms/miles, I reckon that square taper is not quite as bombproof as you suggest!

(This is probably where you reply that we all over-tightened the crank bolts and so the failures were our own fault and not an inherent problem with the design!)

 

[SkipdiverJohn]

I'm gobsmacked with how shite that Cervelo design is, and IIRC Hambini has been roasting them about really shocking tolerances in their BB shells causing misalignment, creaking, and bearing fails. If it was a £99 supermarket BSO it would be bad enough, but on a bike the price of the Cervelo and all these other supposedly "high end" road bikes, the engineering should be impeccable. After all, the customer is paying enough for them, they're not banging out low end stuff that only makes a fiver a frame profit margin.

 

[Foghat]

The video below is a well-reasoned and very plausible assessment of the cause of this well-known failure mode in bonded Hollowtech cranks and, along with other internet sources, worth arming yourself with when having any warranty disputes over replacement:

 

[SkipdiverJohn]

The video below is a well-reasoned and very plausible assessment of the cause of this well-known failure mode in bonded Hollowtech cranks

As I said previously, most modern bike engineering = shite engineering.
This guy is a bit like Hambini without all the swearing!

 

[rogerzilla]

Received wisdom is that most carbon frames, even the top-end ones, are made by Far Eastern plants (Taiwan if you're lucky, China if you're not) for about £50.

 

[SkipdiverJohn]

Received wisdom is that most carbon frames, even the top-end ones, are made by Far Eastern plants (Taiwan if you're lucky, China if you're not) for about £50.

According to Hambini, the exceptions to the Far East rule are Look and Time bikes, still not my cup of tea being carbons, but at least they appear to be able to make them properly and with BB's that are within the correct fit tolerances!

 

[alvintc]

replaced under warranty - result!