[Closed] Cracks in Cranks!

Look like cracks to me. I'll have to check mine now. I wonder what the inside shape of the arm is at that point (i.e. if it's hollow or not there). If it's not hollow there it's a very odd crack location.

Dont think I would be too happy to be riding with those sorts of cracks. Having said that I probably wouldnt notice until I landed on the top tube after a 8' drop with my pedal still attached to my foot but not the crank!

i got 3 chainsets a mixture of XT and SLX, the oldest set are about a year old the newest 3 months, all have cracks in both crank arms.

It's a crack - I wouldn't use them!

Wont be long before they go pop in a painful way. Having snapped a crank arm in the past I can tell you that even on a fire-road it's not a pleasant experience!

Blimey. Not good at all. 😐

Is it ONLY ones with inserts? I've got 3 pairs of Shimano cranks without them. Might check anyway.........

As a structural analyst, even I can't work that one out. you may expect then to crack 90degrees to that due to hoop stress from the thread combined with loading during use, but that is strange.

I shall get my thinking cap on...

Do all of these cranks have inserts for the pedal threads? And if so, are they threaded in, or do they look like they are freeze fitted/bonded?

That's one of two things...it's either the flexing of the inner & outer "shells" of the arm, in effect the insert is forcing the "shells" apart when loaded; or its the "shells" pulling apart because of some inherent stresses from when the insert was put in.
You'd expect longitudinal stress to kick in way before radial hoop stress but that's usually due to internal stresses anyway.
Going to check my Hones tonight, but they were triples so dont think they have inserts.
Get someone to stand on the pedals as you look closely... 🙂

I feel a recall coming on....checks 17yr old Graftons...yep still fine :lol:...weren't SLX the "thinking mans" XTR last week?

Is the arm made up of two longditudinal sections then? Where is the split line. I thought they were hollow forged - which then raises another question - where is the forging split line.

I don't believe that the thread will pull the two sections apart - in fact it will have the opposite effect as it will tend to pull them together against the 'head' of the pedal. However the flexing of the crank away from the frame could place the split line into shear.

monkeyp - I was thinking along the same lines. Odd isn't it. If I get chance and can find a diagram of the internal structure I might model it for a bit of "fun".

All the cranks i have seen with these cracks so far have been ones with the steel inserts, im not sure how my SLX inserts are fitted. I dont recall having to screw them in, my freinds hones that are cracked are press fitted in i beleive.

Id like others to check there cranks.

The split line would indeed be in shear, but I'd have thought there was mroe than enough material to deal with that problem and the insert would help rather than hinder. But if the two halves are joined and then the insert pressed in, maybe the joining and inserting process isn't quite right. Hard to tell, too many variables without seeing it all in reality.

Bugger just ordered an SLX Double Crankset from Merlin. 😐

hmm...18st fat bloke now rushing off to check my 3 sets of Hones.

Ive never heard of anyone ripping the steel insert out of shimano cranks, whatever the model, has anyone else? (someone who frequents MTBR or the DH forums?). I have heard of truvativ steel insert cranks failing tho, quite a lot in fact!

Ive never heard of a shimano crank snapping but by looking at the crack it could happen pretty soon to someone. Ive got this image of everyone rushing home after work tonight to check there cranks.

by looking at the crack it could happen pretty soon to someone

I doubt that TBH. Based on what the OP has said and the amount of people who seem to have cracks in their cranks from such a small sample group, id be amazed if it was not a reasonably common occurence, but with little/no affect on strength, hence the fact no-one has heard of any failures. Of course people should still be complaining to the shop they got them from for a replacement (certainly entitled to one id say).

None of the 4 XTR cranks on my bikes are cracked. Scratched and bashed? Yes! Cracked? No.

Will check in an hour or so. No insert'd ones here though.

bollocks...!
Just checked my slx (double and bash) and the non drive side crank has got a crack in it approx 18mm long 😯

I'd been bigging slx up to everyone aswell saying how strong/light they were for the money, hmmm.
I'll see if i can get a picture up in a min...

I've just posted it up on sdh too, looks like it could be a common problem then;

[url= http://www.southerndownhill.com/forum/index.php/topic,209723.0.html ]SDH linky[/url]

double bollocks. same here, non drive side. Not a good day- cracked dropouts on Fox 36's, now this.

Probably keep riding them til a recall or somebody experiences failure

You can just make it out on these pics;

[IMG] [/IMG]

[IMG] [/IMG]

Looks like they're all going in the same place, in between the two 'grooves', what are these for? something to do with the steel pedal insert?

I think this might need a new thread started with a more informative title- a lot of people who should, probably need thir attention drawn to the thread.

Oh arse - shiny new slx cranks sat downstairs. Now I'm scared to put them on.

Perhaps with my supersmooth riding style they will be ok. 🙂

Anyone [i]not[/i] got cracks?

No cracks on my slx with inserts. Or the old saint, new saint and diabolous cranks either, all have inserts.

Is it just the ones with steel inserts then? My XTR are fine as are the wife's XTs.

Ive emailed Madison but have yet to have a reply. A new detailed thread could be in order.

Yup mine are the same as these both sides have a slight crack/fault line in them, i'll keep an eye on this thread and on the cranks to see what develops.

Phew, just popped out to garage and both sides are a bit battered but uncracked.

Not done many miles on them, week in Alps and a few days back in UK, but a lot of rock bashing.

Paranoia kicks in, off to shed.... cracks as above on XT770 and XT760.
What's going on?

.... cracks as above on XT770 and XT760

Cracks in XT? Can you confirm with pics (just to show others what to look for) as this started off as an issue only on cranks with inserts

I don't have cracks in my SLX cranks. Has anyone contacted Shimano to ask their opinion?

Just checked my Hone, 2yrs old maybe, double with bash.

Definite cracks on one side - same as pictures above, not sure about the other side, its a bit too scuffed to be sure.

Has anyone heard of any actual failures?

I can't believe the amount of posters on here with cracks, it seems that 90% of the people who have read this thread then gone and checked have found cracks!

Has anyone heard of any actual failures?

I'm very interseted in this too.
I've just asked that same question on my sdh post (link on previous post) about slx cranks cracking.
I'm guessing no one has had any fail yet.

[img] http://farm3.static.flickr.com/2798/4016409992_d078ba6871.jpg [/img][img] http://farm3.static.flickr.com/2442/4016410378_721a0467b2.jp g" target="_blank">http://farm3.static.flickr.com/2798/4016409992_d078ba6871.jpg [/img][img] http://farm3.static.flickr.com/2442/4016410378_721a0467b2.jp g"/> [/img]

Photos of the XT770, non drive side. Much smaller than the others, but exactly the same, same chevron lead in, then single crack. you may not see it on these flickr images, but there OK on my big pics.
the 760 is too fine to photo, but pretty sure it will show with dye-pen inspection.

Whats the best course of action for us now then..?
😕

Either get in touch with who you bought in from or try and forget about it and hope they don't break I suppose.

I thought they were hollow forged - which then raises another question - where is the forging split line.

Ive been thinking about this a bit more and i reckon i know what there cracks are. The cranks are made from an extruded tube and i reckon the poster above has got it right, its just the join where the inside surfaces of the tube are squished together, leading to a weaker join in the middle of the crank compared to the solid parent material at the edges. Im (now ive thought about it) pretty sure those cracks wont extend any further than the pictures we have here.

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EDIT: The crack cant easilly extend past the end of the join made in the hollow forge process, it would take a significant impact/force to force the crack to extend into the edges of the crack, prob about the same size force that would snap a normal crank! Of course if the crack entend from the end of the crank arm upto the pedal threads then if your pedal works loose it could have the leverage to peel the front part of the crank arm off (though theyd have been screwed anyway as a loose pedal would ruin the threads)

Those with cracks in XT cranks, can you take your pedal off and see if the crack can be seen in the threads?

Good thinking stato.

Thanks for that Stato - makes perfect sense.