So im new to bikes but I am a mechanic by trade so fixing things doesnt scare me too much so I got this bike the sprocket seems to be broken right at the relief holes (assuming thats the point of them) if I were to bend em back and shoot it with a tack weld... or just rock it? Or how much is it to replace the stack? Is it junk yard parts type thing?

It's possible that those are intentionally placed as shifting aids. It looks like there is more than one. It would be way to much of a coincidence to have such a "failure" occur multiple times on only that chain ring. See if you can't find an internet reference to your specific crank.

You might be able to file/grind it off. Better idea is a new CR.

those are "clean out grooves" designed to evacuate built up gritty chain grunge, etc.
the fact that they are now turning into yawning cracks, and that the teeth adjacent to them are in a different plane, is not good... i don't care if "they were designed that way".. not good.

the large ring appears to be lacking shift aids other than old style ramps, too...
modern pins and ramps, with lifting cutouts, will greatly improve shifting to that ring.

Huh? You usually offer sound advice, but not this time. These are merely "bargain" shift ramps for low-end chain rings. Nothing more. They're made to assist the chain as it goes up or down to an adjacent chain ring while shifting.

Higher end rings will instead have machined cut-outs (like you see on your cassette cogs) and even pressed-in steel pins to act as ramps for the chain. (Edit: I see Maddog34 said as much at the end of their post. Sorry.)

Nothing to worry about.

physical openings in the valleys of sprockets are known as "clean out grooves".
i've worked with PBI to help create new sprockets, 30+ years ago.
the trick with those was balancing cleanout vs. wear.. and also we worked on making the sprockets more quiet during use, RE: tooth tip relief/release angles.
i tested a dozen prototypes... one stood out RE: noise, and an alternating left/right groove at about 1/3 total sprocket width seemed to balance the down-wear thing.
i got free sprockets and chains for two years.

the thing i see that is a problem on the chainrings in discussion is the tooth mis-alignments happening.
one even looks to have opened the groove up some too..

maybe sweeks can give the ring braces.?.

Sorry... all I can give it a root canal treatment.

Believe it our not, you don't need all your teeth. A missing tooth here or there isn't really a deal at all because there are so many others.

Compare to a couple other bikes of like "prestige" and see if they have the same "quirks".

As a dentist, I'd prefer if you specified that these are *chainring* teeth.

It reminds me of a dental joke, though: "Be true to your teeth, or they'll be false to you!"

You are correct. These are not the most elegant of shift ramps but they are common on cheap steel chainrings. You can see another one on the same chainring with about the same gap. They are there for a benefit and not a flaw.

I’m not sure that has moved out of the plane of the ring. Does it work ok?

Those are the lift pins. Maybe not as elegant as those found on more expensive chainrings but they serve the same purpose. If they were “yawning cracks”, why are there 3 identical ones in the picture? They are also positioned where you would find pins in the more expensive chainrings



Here’s two other chainrings with similar structures but of a higher quality. A bit more refined but they are there for the same purpose…to lift the chain and aid in shifting. Removing them by grinding them off would be a huge mistake.

It's an inexpensive part...just replace it and be done with it...or spend hours being irritated that you can't get it 'right'...your call

Given that the crank uses steel rings, it is unlikely that they can just be replaced. It would require an entire crank set which is a more expensive proposition. There really is no need for replacement since those cutouts are there for a reason. In other words, it ain’t broke so there’s no need to “fix” it.

cyccommute is right, as usual. The manufacturer chose the cheapest possible method to incorporate shifting aids into the chainrings. Aesthetically ugly, but the bike shifts better than it would otherwise, and will continue to do so more or less indefinitely.

You have to admire the engineer who thought of it. Like Tom Ritchey popularizing the unicrown fork. Some people hate the look of it, but it's light and strong and is probably at least somewhat less prone to failure than conventional forks.

If everything works. Just ride it until it doesn't work. Replacing things that only don't look right will get to be expensive. It doesn't save you money to fix things that aren't causing issues.

did you notice the LACK of gap on the big ring's cheap stamped shift aid "pin" ? (top picture, top red circle).

so, i dug around thru my collection of old MTB cranksets, and found one similar to Kmeyer's... it has the same thing showing, minus some wear... it is an old Alivio crankset, the adjacent teeth are the same height to the right, not worn lower, as pictured by Kmeyer.
Shimano Alivios of that age have Replaceable steel rings, but in a ridiculously tiny BCD size, and all three rings are held in place at that 67mm(?)BCD. (Sheldon's math says it's 67.66mm, so may be 68mm too... )

Sheldon's cribsheet doesn't list that BCD...
https://sheldonbrown.com/cribsheet-bcd.html

if an old crankset has replaceable rings, and measures about 39.8mm between adjacent bolts..... when it is decided you need to replace rings, replace the entire crankset, and enjoy modern shifting.

Did you not notice how the gap on both lift pins on the smaller ring are about the same width of a gap? They look relatively identical to me. The one on the outer ring may be smaller because it is on the outer ring or it may be a perspective issue. The larger ring’s lift pin is mostly out of the frame of the picture.

Kmeyer93’s rings aren’t don’t look very worn at all. Not sure what you are trying to say, however. So you’ve found a ring that has the same pins but they aren’t by design?

Please quit trying to stretch every response into a lengthy discussion, and adding pointed false assumptions. Thanks.
the rings shown by Kmeyer93 appear to be identical to the nearly un-used ones i have here, except for obvious wear on many of K's rings' teeth... which isn't super-bad wear, but still quite obvious, if you know what to look for. PS.. that wear varies from tooth to tooth, making it not as obvious to untrained eyes.
look closely.. you'll see that the rings bolt up at a very small BCD.. just like the early Shimano MTB alivio crankset i have in stock.
those alivio cranksets had a Decal on the outer face of the arms that got wiped off most of them by shoe rub.
there is no Shimano parts Code on the back of the arms.
the mid and big ring have a few "W Cut" teeth, meaning they a tiny bit shorter, and are flat on top, until they wear some after a few thousand shifts....
the W Cut teeth are not adjacent to the cheap stamped shift "pins".

obvious conclusion: i have the un-worn version here to look at now, from any angle i choose.
Ideally, the worn rings should be replaced, but are not critical at this time.
that BCD has never been covered by the aftermarket in this century, and Sheldon never recorded that BCD.
When Replacement is Needed, just Install a newer design crankset, with more modern, better shifting.

break's over.. back to work on a fairly well preserved K2 ZED MTB.

Please quite trying to cast aspersions. Mine is not an untrained eye.

You extrapolating a whole lot from a couple of very close pictures. There is no picture of the outer face of the crank so how can you tell if the crank is an Alivio or some other generic crank. There is no picture of the crank arm from which to tell if there is a code or not.

But all that means nothing. You said

They aren’t “yawning cracks” and are nothing to worry about.

Not in the pictures I’ve seen. The teeth look pretty much the same size all the way around. Compare the teeth to the photos of chainrings I posted.


Brown did record the BCD



Granted, the chainring has a really weird BCD that is a dead end. But there is no need to replace anything…nor worry about a problem that doesn’t exist. Those are steel rings that are barely worn and don’t need to be replaced anytime soon. Those rings probably won’t need to be replaced for decades of hard use with just a modicum of care.

My objection here is the advice you are giving that this feature is a problem and needs to be addressed. It isn’t and doesn’t.

now you want to argue with what i just saw on my desk, moments before i posted about it... about something you can't see or know about.
not cool, stew.
bordering on blatant trolling.

and that's a completely different chart.
at least you did something good.

bye bye.

We aren’t discussing what you saw on your desk. We are discussing a couple of close up pictures posted by another person which you can’t see or know more about it than I do. And, again, your observation that there is some kind of problem with the chainrings is still wrong.

I know it is a different chart. But it just shows that the BCD was recorded by Sheldon Brown

​​​​​​​We’ll see.

For what its worth, my cost to replace the part you are talking about was $35. This included all three rings and both crank arms from a name brand (Shimano) brand new from a legitimate site. They sometimes came in my choice of black or silver. An easy DIY job, but one special tool is likely required to remove the old crank arms.

Fantastic! You are going ta have a blast. Bikes are easy. Especially the ones with no electronics. As to the OP, I would just buy another Crank or Replace the Crank Ring. Looking forward to seeing some of your fixes. Please Post...