Broken Crank After Second Ride :(

Postby nzryan on Mon 30th Oct 11:27am

Hey guys,

I made a post a while ago (new-riding-t103707.html) and while I didn't get the bike until about 1.5 years ago from today, I started riding now that I got my weight back down.

I purchased a Jamis Roughneck after 3 visits to Pukekohe Evo Cycles, although I won't be returning there as the sales team there seem to not be interested in any customers that aren't in their "clique". Found them short on information when questioned, just wanted to push the sale and they tried to take the factory seat when I upgraded to something more beginner friendly (they must do this a lot and try and re-sell them, they we're quite dumfounded when I hit them up about where the seat was....)

Anyways I've riden this bike twice, once when I first got it, was on a low tide beach out west which lasted a total of 30 minutes of slow single gear riding. Then yesterday I went to a industrial park and did 40 minutes of road riding on pumped tires (15psi) and during a gear change I found the main crank chain not attaching correctly, I had to get off and fix it on then pedal to make the change, on finishing I was having a look at the crank and noticed the metal is cracked, it's very obvious that it's a stress crack as the patern goes around in the same places and where the crank is fixed to various parts.

I know i'm a big boy, but what forces may have caused this? I've never sat off the bike seat, so have not been standing on the pedals, never thrashed it as I can't do that yet, just been cruising enough to break a sweat.

I don't believe this will be under warrnaty now as it's 1 year for these parts and I don't want to deal with Evo cycles any more, happy to pay for a new one, but don't want to replace with the same thing, what can I do? I need something stronger I guess? Any help/suggestions?

Image
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Re: Broken Crank After Second Ride :(

Postby Conners on Mon 30th Oct 1:02pm

Hi Ryan,
It's hard to make out from your description and photos what is actually broken.

Couple of questions/comments from your description that might help to clarify:
I think you're talking about the chain rings rather than the cranks - cranks are the bits that the pedals bolt to, chain rings are the toothed wheels that the chain runs on. Does that sound right?

When you say "during a gear change I found the main crank chain not attaching correctly" I think you mean that the chain wouldn't shift up from the smaller chain ring to the larger one - and you had to stop and shift this manually?

It would be great if you could circle the points on the photos where the cracks are - might be easier for someone to diagnose what's going on.

As an aside, it looks like there is a fair bit of sand and grit from that beach ride on your chain and chainrings. Would be a good idea to give that a good wipe down and re-lube, the sand will wear out your chain and chain rings really quickly if you leave it on there.
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Re: Broken Crank After Second Ride :(

Postby philstar on Mon 30th Oct 1:31pm

Conners wrote:Hi Ryan,
It's hard to make out from your description and photos what is actually broken.

Couple of questions/comments from your description that might help to clarify:
I think you're talking about the chain rings rather than the cranks - cranks are the bits that the pedals bolt to, chain rings are the toothed wheels that the chain runs on. Does that sound right?

When you say "during a gear change I found the main crank chain not attaching correctly" I think you mean that the chain wouldn't shift up from the smaller chain ring to the larger one - and you had to stop and shift this manually?

It would be great if you could circle the points on the photos where the cracks are - might be easier for someone to diagnose what's going on.
.


2nded

check the chain ring bolts are tight.

Conners wrote:As an aside, it looks like there is a fair bit of sand and grit from that beach ride on your chain and chainrings. Would be a good idea to give that a good wipe down and re-lube, the sand will wear out your chain and chain rings really quickly if you leave it on there.


wipe the chain with a cloth dampened with degreaser the re lube (if beach riding the I would recommend a dry lube)
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Re: Broken Crank After Second Ride :(

Postby nzryan on Mon 30th Oct 10:05pm

Hi,

Yes sorry never actually looked into terminology but it seems like it would be a very good idea :)

Yes it's the chain ring, when I was changing from the smaller one to the larger one, I could see the chain had started to shift, but would drop right back down and make a horrible noise, until I manually forced it to go on. I think that's when the chain ring cracking started, not sure how but yeah.

Here are some more pics: https://imgur.com/a/J4qji

Hard to see but these are the cracks in the ring, looks like the metal has stressed and it's got oval shaped cracks where the metal has split;

Image

Will look into the sand stuff, chain bolts seem to be fine, will head to a shop this weekend and pickup some maintenance kit and tools, anyone recommend a decent shop in Greenlane area that are not in for the sell?
nzryan
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Re: Broken Crank After Second Ride :(

Postby Velocipedestrian on Mon 30th Oct 10:13pm

Still can't see the cracks... I can see normal chainring shaping, is that what you're looking at?

Not shifting up from the smaller to the larger ring is just a poorly adjusted shifter/derailleur.
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Re: Broken Crank After Second Ride :(

Postby AgrAde on Mon 30th Oct 10:21pm

There's nothing wrong with your chainring that I can see.
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Re: Broken Crank After Second Ride :(

Postby Conners on Mon 30th Oct 10:45pm

Yeah I think what you might be seeing is just scuff marks in the black coating on the chain rings (to be expected as the chain has to touch the inside face of the larger chainring as it is forced up and onto that ring). All of that shaping that you can see is part of the design and helps the chain move from one chain ring to the other.
Totally normal that a black chainring doesn’t stay black for very long.

Agree with velo, your shifting problem sounds like a derailleur adjustment issue (not enough cable tension). Also pretty normal on a new bike, cables stretch (actually the outers compress) and can need tweaking after a few rides.
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Re: Broken Crank After Second Ride :(

Postby jo on Tue 31st Oct 9:01am

:withstupid:

The difference in tooth size on that chainring is also part of normal design. :)
https://www.purecycles.com/blogs/bicycl ... rings-work
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Re: Broken Crank After Second Ride :(

Postby nzryan on Tue 31st Oct 9:40am

Errr I though the entire chain ring would need to be one flat peice of metal, or at least stamped a little to fit parts/design look? I'm not worried about the teeth, it's the metal part below them that forms the disc, it's cracked all the way around.

These oval lines you see inside the red are sharp bits of metal that have snapped away from the opposite side, is that normal?
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Re: Broken Crank After Second Ride :(

Postby Rik on Tue 31st Oct 9:45am

jo wrote::withstupid:

The difference in tooth size on that chainring is also part of normal design. :)
https://www.purecycles.com/blogs/bicycl ... rings-work


That's a good 101 on chain ring shifting design. Read the bit at the bottom about shifting ramps, I thinks that what you seeing.

BUT you might be seeing something that we can't in the photos. The best way to determine if it's a crack or normal chain rub is grab the chain ring with a pair of pliers and gently wiggle it side to side, if the silver line gets wider, it's a crack.
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Re: Broken Crank After Second Ride :(

Postby Velocipedestrian on Tue 31st Oct 10:09am

nzryan wrote:These oval lines you see inside the red are sharp bits of metal that have snapped away from the opposite side, is that normal?

If that's what's happened, no. But that isn't what it looks like from the pictures.

Take Riks advice, pliers and wiggle, but consider if the gap doesn't widen we could be right.
Then it's just gear tuning.
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Re: Broken Crank After Second Ride :(

Postby AgrAde on Tue 31st Oct 10:53am

HTH

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Re: Broken Crank After Second Ride :(

Postby jo on Tue 31st Oct 10:57am

nzryan wrote:Errr I though the entire chain ring would need to be one flat peice of metal, or at least stamped a little to fit parts/design look? I'm not worried about the teeth, it's the metal part below them that forms the disc, it's cracked all the way around.

These oval lines you see inside the red are sharp bits of metal that have snapped away from the opposite side, is that normal?

The oval lines, as shown in your pics here https://imgur.com/a/J4qji are completely normal.
The black anodising has come off which makes it look shiny. Take Riks advice tho to check.

Many chainrings used to be stamped sheets of metal, but many others are machined (with the advent of CNC machining it produces a better result at a reasonable cost). Some are stamped, then machined. There are usually a few pins as well to help the chain along.
I remember some durace chainrings that got made abit thin and they folded.

I took a few photos from the work bike room so you can get a sense of the variation in how the manufacturers addressed ramps.
20171031_103122sml.jpg

20171031_103300sml.jpg

20171031_103330sml.jpg
jo
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Re: Broken Crank After Second Ride :(

Postby jo on Tue 31st Oct 11:04am

Also zoom in on the reverse side image in this link for what its meant to look like.

https://www.amaincycling.com/fsa-comet- ... 41/p308415
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Re: Broken Crank After Second Ride :(

Postby Conners on Tue 31st Oct 11:26am

also - if the teeth on your chain ring look like the middle ring in the photo below, you've left it too long to replace your chain and will be shelling out for a whole new drive train :lol:
DSC06529.jpg
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