chain grinding against guard sprocket?

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1/2/2020 7:11 PM

This sprocket is only a couple months old, the chain only a few weeks older and only ridden on this sprocket and another sprocket that was only ridden for maybe 2 weeks (I bought it, then swapped it out for the Odyssey La Guardia sprocket since that one I could run backwards a la Ian Schwartz)

and it's still making that god awful grinding noise from wearing in after all these months. Granted, I haven't ridden as much as I'd normally be since I'm still rehabbing a torn ACL, but I still get out and pedal around. I replaced the chain tonight and at first it was really tight but made minimal noise. I loosened it a hair because I like doing crankflips, and the noise was back worse than ever.

so I examined the sprocket and it looks like there's wear marks on the inside of the guard from the pins rubbing against it at times, but when I try to push the chain against it, it doesn't touch. So the only thing I can come up with is as it's rotating and coming off the sprocket and going towards the driver (not literally popping off the sprocket, but rotating as normal) it's rubbing against that causing the grinding noise


does that sound like it could be causing my issue? Because I am fucking stumped. The driver is a couple years old, but not visibly worn just yet. Chainline is perfect. Sound is 100% not coming from the driver/BB bearings or anything like that.


I'm just trying to get to the bottom of this because it's driving me fucking crazy and should've worn in by now but still hasn't. I put my old Animal sprocket on but haven't ridden it yet, so not sure if that'll make noise but it didn't before so we'll see. I'd really like to find a solution because while I don't do crank arms/sprocket stalls, I do crooks a lot and sometimes when I slip out of them I bash the inside of the sprocket, hence running it on the inside, so flipping it and running it normally is something I don't want to do. The only thing I can think of is putting it on a lathe or something and machining a little bit of the inside material off so it doesn't rub anymore but that seems a little drastic

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1/2/2020 7:36 PM

That does sound weird... and the sprocket is 100% not bent?

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Scooter kid trying to ride a bike. Instagram: @scootereyn // YouTube: RH MEDIA

1/2/2020 7:54 PM

Sprocket is 100% not bent at all, there's not even any dings on the guard part because I haven't even gotten to use it outside of pedaling around

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1/2/2020 7:56 PM

Do you have pics?

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1/2/2020 8:21 PM

Super-Pawl wrote:

Do you have pics?

of the wear or what? cause I took it off and put my Animal one back on till I get this sorted out


And yes it is painted but for one it should’ve been ridden enough to wear the paint off where it needs to by now, and two I never had this problem with my Animal sprocket when I painted that so I highly doubt it’s the paint. You can see it’s worn through the paint and original black anodizing to the raw metal, but again the pins did not touch when I tried pushing the chain against it since the teeth stop it. Once it comes off the sprocket and goes towards the driver is the only place I got the chain to touch that and even then I had to push and hold it

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1/2/2020 9:30 PM

Maybe the chain doesn’t actually shift over but it like, leans at an angle under pressure when you pedal?

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Scooter kid trying to ride a bike. Instagram: @scootereyn // YouTube: RH MEDIA

1/2/2020 9:39 PM

readybmxer wrote:

Maybe the chain doesn’t actually shift over but it like, leans at an angle under pressure when you pedal?

I can see that, while pedaling, the chain is tighter on top, and could be bowing out on the bottom slack side..

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1/2/2020 9:45 PM

readybmxer wrote:

Maybe the chain doesn’t actually shift over but it like, leans at an angle under pressure when you pedal?

that's the only thing I can think of. I put it on a bike stand and pedaled it, forward and backward, and it wasn't rubbing... so my only guess is the added pressure of my body weight somehow causes it, but I have no way of troubleshooting that cause it's in such an awkward area to look at while pedaling it. Even still the chain line is perfectly fine.

then comes the problem of thinking of a solution to this if that is the issue. I can't move the sprocket in any further cause I already had to take the cone spacer out on that side to perfect the alignment, and the guard part itself is already super close to hitting the chainstays...


I guess I could try to find a chain with shorter pins to troubleshoot that. the one I have now is a Primo 510. I'm just at a loss for a solution. It's not the end of the world if I have to stick with my Animal sprocket, just really annoying when I slip out of a crooked grind and break the chain haha

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1/3/2020 12:13 AM

Have you tried not running it backwards? I know you said you're against it, but I've ran the la guardia with a halflink and have zero rub on the guard.

Havent broken a chain since 2009ish and I love sprocket stalls and crooks/crook 180s

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1/3/2020 12:24 AM
Edited Date/Time: 1/3/2020 12:26 AM

I'd try another chain. A friend of mine had just barely tweaked his chain and it had worn like 4 teeth on his sprocket almost all the way down before he realized what was happening. That was with a sprocket with no guard though but I figure the chain was being pushed all the way over against the side of the teeth real hard when the chain would tension up while pedaling.

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1/3/2020 1:10 AM

HtownGetDown wrote:

Have you tried not running it backwards? I know you said you're against it, but I've ran the la guardia with a halflink and have zero rub on the guard.

Havent broken a chain since 2009ish and I love sprocket stalls and crooks/crook 180s

I have not although I should've. I didn't think to do so until I'd already put everything back together then was too lazy to take it all apart again... I'll have to give it a try to troubleshoot.

I break rarely actually snap chains but long crooks and 180 to crook are what I always slip out of then end up sliding on my sprocket/chain and end up with fucked links that need replaced. like I said it's not a huuuge end of the world, just annoying to deal with

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1/3/2020 1:14 AM

quick16g wrote:

I'd try another chain. A friend of mine had just barely tweaked his chain and it had worn like 4 teeth on his sprocket almost all the way down before he realized what was happening. That was with a sprocket with no guard though but I figure the chain was being pushed all the way over against the side of the teeth real hard when the chain would tension up while pedaling.

I did that already just tonight, I mentioned in the original post I tried that and initially it seemed quiet but I didn't really hard crank on it either, then when I loosened it a hair and pedaled the 2-3 miles home it was making the grinding noise the whole way there but worse

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1/3/2020 4:27 AM

Does it happen under a sit-down pedal/very light pressure or just when cranking hard? (I know, BMX bike are "not designed for that" )

My old MDS did the same thing to the original owner, then me when I was on a Shadow Interlock 2 (they have some long pins). I swapped to a bluebird and don't recall issues at all.

If you have ANY way to mount like a go pro or your phone to your bike aimed at the top of the chain (so on the seatpost so the video is clear) and or a back drive side peg and pedal around, you could diagnose it.

I would bet you have some minor frame flex when cranking hard.

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1/3/2020 5:43 AM

Looks to me like the chain-line is off enough to make rub. if you turn it around, you wouldn't notice.

maybe you have a little spacer you can remove on drive side?

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1/3/2020 6:29 AM

dave lawrence wrote:

Does it happen under a sit-down pedal/very light pressure or just when cranking hard? (I know, BMX bike are "not designed for that" )

My old MDS did the same thing to the original owner, then me when I was on a Shadow Interlock 2 (they have some long pins). I swapped to a bluebird and don't recall issues at all.

If you have ANY way to mount like a go pro or your phone to your bike aimed at the top of the chain (so on the seatpost so the video is clear) and or a back drive side peg and pedal around, you could diagnose it.

I would bet you have some minor frame flex when cranking hard.

hmm not sure about sitting down, I’ve only done a little sit down pedaling with it since my knee lacks that tiiiny bit of flexion to sit down and pedal without it hurting yet. I remember doing it a couple times just to see if I could but don’t recall the noise, I’ll have to try again and see whenever it decides to stop raining here. Also gonna check and see if maybe the pins on this chain are longer than most others.


I thought about the GoPro thing but unfortunately the mounting tabs on mine broke off and it’s one of ones that’s built into the case/can’t be replaced (Been meaning to superglue new tabs on again) so that’s a no go but I’ll try to rig something up and see

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1/3/2020 6:32 AM

jmz313 wrote:

Looks to me like the chain-line is off enough to make rub. if you turn it around, you wouldn't notice.

maybe you have a little spacer you can remove on drive side?

nah I have a thin spacer but taking that out causes the sprocket to rub the BB shell /:

it’s most definitely the chain line being sliiightly off the more I think about it, even if it doesn’t look it

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1/3/2020 7:22 AM

chainline? how does that look. what chain are you running? have you considered switching to a basic kmc chain? you have a guard and you dont run it tight so no reason to really worry about snapping it from torque.

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1/3/2020 7:11 PM

This same exact thing happened to my old MDS when my chainline was off. I just got used to it and rode it that way lol.

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1/4/2020 6:44 AM

I checked my La Guardia out of interest, and it is showing something similar, but to far less extent. Haven’t heard any noise though.


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1/4/2020 7:41 AM
Edited Date/Time: 1/4/2020 7:57 AM

Looks like the pins start to dig into the sprocket upon each revolution then stops ^

currently troubleshooting, it’s definitely binding in or something cause if I take my finger and push the chain over it rubs the same area and the pins catch the edge of the guard, but requires a decent bit of force to do so. chainline is pretty good but could be a tad better I guess. Makes normal “chain wearing in” noises when the guard is run normally, presumably from the chain wearing it in on that side




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