What Happened?

egasa

On the bike (Trek Madonone 3.5) and all is well. Stand on the pedals for a wee rise in the road and something snaps. Next moment I'm lying in the road. Left pedal is somewhere up the road with part of the snapped crank set and bottom bracket bearings attached.
So, what happened?
Did the bearings from the press fit (Hope PS 41 BB - installed at the start of the year) BB come out and cause the crank set to snap?
Did the crank set (Ultegra 6750) snap from fatigue (bike only 2 and a half years old) and pull the bearings out at this point?
Or something else?

The bearings in the BB are running smooth, so do I now just get a news crankset, fit it and the bearings for the BB and get on with things? Did I I not install the BB correctly (followed the instructions very carefully and used the Hope press fit BB tool)? Clearly, I don't want the same thing to have any chance of happening again.

Took the snapped chain set into a local bike shop and the guy there said he had never seen something like this before.

Some many questions folk.? Any answers or opinions to help to ease my worried brow?

Thanks.

lawrences

Sounds unfortunate.

But considering none of us saw it we will have far less of an idea than you or the bloke at the bikeshop.

me-109

Was any of the BB axle inside the l/h crank? Did the axle snap or did the crank just come off the end?

egasa

The BB seems fine and was not inside the left hand crank.
The axle snapped on the crankset, as shown.
Oh, and lawrences, you don't have less of an idea than me what happened because I haven't a scooby.

lawrences

I now have an idea don't worry.

Your axle has broken

Big legs!

sloppyschleckonds

Just how much power were you putting out at the time!?

epo.wks

It probably snapped because "what to happened" makes absolutely no sense.

egasa

SloppySchleckonds wrote:

Just how much power were you putting out at the time!?

I have been telling folks that the problem is simply one of awesome power, but they're not buying it.
In reality, not a great deal of power was going through the pedals at any time on the ride.

egasa

epo.wks wrote:

It probably snapped because "what to happened" makes absolutely no sense.

Hmmm. What to say. Oh yes, got it.

epo.wks wrote:

A+ contribution - would seek your opinion again and again.

desweller

I would hazard a guess that either the bearings were not concentric enough, causing the crankshaft to undergo a cyclic bending moment on every revolution leading to a fatigue failure, or the crankshaft had a crack or other flaw in it before installation.

I don't have one, but I think the Hope tool serves to ensure the bearings are parallel and concentric during installation, no? So you probably just had a dodgy one.

Ouija

24mm HTII axles have been known to twist under load which was one of the stated factors in other companies designing the BB standards based around 30mm axles (BB30, PF30, BB386 etc).

Grill

Ouija wrote:

24mm HTII axles have been known to twist under load which was one of the major factors in other companies designing the BB standards based around 30mm axles (BB30, PF30, BB386 etc).

Reference? They seem to take 2000w sprints without any trouble...
That's not why 30mm came about...

simon_masterson

I broke a fixed cup once - sometimes things break out of the blue. No suspect creaking or play in the last week? Glad you're ok; it could have been much worse.

egasa

No creaking or play at all. All had been going very smoothly, even on the 'fateful' ride.
I've taken the broken crankset into a couple of shops and all 4 mechanics have said "wow, never seen that before".
I'm going to get the new crankset, fit it with the current BB and keep an eye on it every so often.
And as Simon says it could have been much worse. Went by the scene of the incident today and had a wee look over my shoulder before getting on the pedals. 4 or 5 cars immediately behind. Made me shudder to think that could have been the case last week. However, it wasn't and all is well.
Thanks for your opinions folks.

damocles10

First thing....pleased you are OK. It could have been a bad crash.

Secondly, I would show the pic to Shimano, I am sure they would be very interested if there is a fault with their product. Cranks don't usually snap like that. Get a mechanic to look at the bb section on the frame, it may be slightly off increasing fatigue in the materials.

Guernsey Donkey

It's difficult to see in that photo but there appear to be brown marks on the inside of the tube.

Is it rust/corrosion?

Ouija

Grill wrote:

Ouija wrote:

24mm HTII axles have been known to twist under load which was one of the major factors in other companies designing the BB standards based around 30mm axles (BB30, PF30, BB386 etc).

Reference? They seem to take 2000w sprints without any trouble...
That's not why 30mm came about...

Cannondale vice president of R&D, Chris Peck (on their reasons for designing BB30)

"[Our] Hollowgram SiSL2 crank with SpideRing weighs 484g. By comparison, new Dura-Ace 9000 weighs around 678g. In addition to weight, another BB30 advantage is stiffness. By increasing the spindle diameter, you increase its resistance to twisting, which is where the bulk of the deflection in a crankset comes from. Roughly 70 percent of total deflection measured at the pedal comes from axle twist."

Dura Ace 7900


Deore XT

desweller

That statement is just saying that it's stiffer, not that it's stronger.

All shafts show strain when a torque is applied. Manufacturers could have just increase the shaft wall thickness if they wanted to make it stronger. BB30 is a cost-saving exercise that happens to be marketable.

Grill

You have 3 examples of the most sold standard on the market. Hardly a proper sample. Also the majority of pros are using it. If Degenkolb and Kittel can't bust them in a sprint, we have nothing to worry about.

BB30 was developed to save money. Fact is the tolerances are terrible, and the longevity is iffy at best.

As for stiffness, take a look at Fairwheel's latest crank review. The chainsets with the least amount of deflection all had a 24mm spindle (the Ultra Torque is 25mm, but close enough).
http://fairwheelbikes.com/c/forums/topic/crank-review-5-2/http://fairwheelbikes.com/c/forums/topic/crank-review-5-2/

Ouija

Merely pointing out that 24mm axles can break. If i can find two examples in under a minute then i'm sure there are loads more people who just haven't bothered taking pictures of it and plastered them all over the web.

Grill

So can 30mm spindles. Fact is everything has a breaking point, but when your sample size is 50 times larger it's easier to find examples. I can't find any other examples besides the ones you posted (2 are from the same source) and the circumstance surrounding the breakages are unclear. No point scaremongering over something that isn't actually an issue.

egasa

Guernsey Donkey wrote:

It's difficult to see in that photo but there appear to be brown marks on the inside of the tube.

Is it rust/corrosion?

A little corrosion which appears somewhat superficial, but then the axle did break so maybe not so superficial.
How many people give the inside of their cranks a regular clean out though?

Old_Timer

Another "Glad you weren't hurt" here.

Is there any chance there is a university near you with an engineering department? Or a materials testing laboratory that can do analysis of structural steel and bolts/connectors for the construction industry? A metallurgist could look at the break and the strain/stress marks and tell you a great bit about why and what happened. At least you would know what to pursue and if you did something to cause this breakage. From the metals failure analysis I have seen in my profession (Quality Engineer in construction) this is most likely a faulty spindle (BB axle) and not something you did or didn't do. A true materials engineer or metallurgist could quickly tell you what is going on. Not to make you spend any money, just get someone's professional curiosity going and they should look into this for you.

Best of luck on finding out what happened to cause the breakage.

AhoyAhoy!

A sensible suggestion from Mr Old_Timer. A vague memory from my Engineering degree is that failure in a 45 degree plane is due to excessive torque / fatigue. So either the op has a tremendously stompy pedal stroke, put a massive 'notch' into the axle whilst assembling it, or there was a manufacturing flaw in the component to begin with. My money is on the latter.

Guernsey Donkey

Corrosion is a big problem on parts that are subject to stress and are likely to lead to fatigue cracking.

If you do a google search on AAIB, corrosion and fatigue you will find many many reports that mention the connection. One of the first reports to come up on google is this one which covers the ditching of two helicopters in the North Sea. http://www.aaib.gov.uk/publications/for ... g_chcn.cfm

Corrosion and stress do not mix.

Old_Timer

Just from looking at the attached pictures of the failed spindle, there isn't evidence of corrosion being at fault. If the brownish red spot on the spindle still attached to the cranks and chain rings is what some are going by to suspect corrosion, its a surface stain, and not a penetrating rust area. Looking at the metal on both spindle sections at the break there isn't corrosion penetrating or degrading the metal. That said, these are small, relatively unclear pictures so analysis by looking at them isn't any kind of certain. The tensile strength of the spindles should far exceed the force the OP could exert, even with the factor of the crank arms being levers. Although for all I know the OP may well be one extremely large and inordinately strong chap. :shock:

I wouldn't disagree with the corrosion and stress being a bad mix, it just doesn't look like corrosion was the culprit here. Those North Sea Helo losses were aircraft subjected to very high stress levels and extreme salt corrosion possibility from the sea environment. That environment is why Naval and commercial operations over the water should all have very strict corrosion control programs. This is actually a rate specialty, or a trade, in the US Navy, and in the Royal Navy, I am sure, too

Try looking for reports of other spindles of this manufacturer failing on the web in various forums and such, if its wide spread there will be reports as no one buying this crankset wants to hide this type of failure. they are most likely going to be like the OP and wonder what happened, as his title says. I hope that the answer comes to light and is posted here so we can know exactly what to watch out for.