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Oldguyjon Oldguyjon
7/9/2017 2:19 PM

So last summer my front sprocket went wobbly - the chain would tighten and kink at the same point of rotation. I took it off and the hole had been chewed out,competewith little spirally aluminum bits. No amount of tightening would fix this. So I out on a new sprocket.All was good. I was out today and felt the same stickiness in the drive train. it sunnerivng because it pops or resists at just the wrong time. Pedaling backwards, Ican feel the tension at one spot. But the worse is, I can see a spiral of metal coming up from the sprocket. So it's eating itself again.

Now I also had my non drive side crank arm loosened up a few times last summer. Andit just happend again last week. I now have loc-tite on it and check it religously. Is this related?

Why are my cranks eating sprockets?

Silver sprocket is old one, see how the mouting hole was chewed out a little. Photo

Second pic, the new red sprocket, has a a little sliver bit of metal creeping up...I know what that is....


Photo

New tech can't beat old school cool...or can it?
1987 O.O.S. Redline RL20II (Old Old Stock - this ain't no museum piece kids!)
2012 Norco Deviant
1996 GT Avalanche LE w/ Full 2002 XT upgrade and NE Total Air MZO fork

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alexnjbmx alexnjbmx
7/9/2017 2:31 PM

it seems like you dont have a sprocket spacer/adapter. it keeps the sprocket centered on the spindle.most sprockets come with one

refs: justridebmx, four, kingpin, Alex_DeWitt, Michael_Howard, bmxrider000, TokenBMX(x2)
member of the week 2/22/10 - 2/28/10

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alexnjbmx alexnjbmx
7/9/2017 2:33 PM
Photo

refs: justridebmx, four, kingpin, Alex_DeWitt, Michael_Howard, bmxrider000, TokenBMX(x2)
member of the week 2/22/10 - 2/28/10

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Oldguyjon Oldguyjon
7/9/2017 3:08 PM

Well I wish it was that easy!

I removed the spacer to show the damage on the sprocket. As you can see, the old spacer looks great, it's obviously made of tougher stuff than the sprocket itself. The new spacer that came with the new sprocket is mounted on the bike.

So, assuming the spacer is in place, back to the original question: Why is the sprocket getting eaten? Should I just budget a new sprocket every 3-4 months? Buy in bulk? Can I get a 5 pack?

Photo

Photo

New tech can't beat old school cool...or can it?
1987 O.O.S. Redline RL20II (Old Old Stock - this ain't no museum piece kids!)
2012 Norco Deviant
1996 GT Avalanche LE w/ Full 2002 XT upgrade and NE Total Air MZO fork

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alexnjbmx alexnjbmx
7/9/2017 4:08 PM
Oldguyjon wrote:

Well I wish it was that ...more

hmm im kinda stumped. dont really do much with bmx anymore. if this was 7 years ago id probably remember more bike tech info . from your picture it looks like that spacer is moving around. maybe your cranks are too tight. maybe try putting a spacer between your sprocket and bottom bracket. that could be the issue

refs: justridebmx, four, kingpin, Alex_DeWitt, Michael_Howard, bmxrider000, TokenBMX(x2)
member of the week 2/22/10 - 2/28/10

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weegaz22 weegaz22
7/9/2017 4:16 PM

I don't know if its the angle of the pic but if you look at the red sprocket pic the chain looks like its too much over to one side of the sprocket teeth which is probably why you have gouges out of your other sprocket, could be a chain run issue due to sprocket not being spaced out properly, so you might need to some additional shims to space the sprocket out more from the BB as it could be too tight up against it, if you only have the sprocket spacer hard up against the cone shaped cover that covers the bearings then your going to be grinding that cover down, if you have 2 really thin shims in between the cone shaped cover and the sprocket spacer they will help add additional slippage between each other. get a pic up of your bearing cover, could be that is whats grinding down



head to 7:31 in that video, he has one or 2 spacers on top of the sprocket spacer.

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Oldguyjon Oldguyjon
7/25/2017 9:06 AM
weegaz22 wrote:

I don't know if its the ...more

(Following up in case someone else has this issue)

Thanks - this was the issue, in a weird way. The red sprocket was really bad, loosening the chain so much it was skipping the chain stays and then binding tight. So I grabbed a new sprocket and my LBS (shout out to Joe Mama, Ottawa, Canada) who gave me some spacers to try as well.

I tried them and the issue was that the sprocket was too far away from the frame, not too close. If I used no spacers, I could feel the chain grind when pedaling in reverse. I felt this when I installed the red sprocket. I checked the rear wheel, but I don't see any way to shift the free wheel. I do vaguely recall having to use my wifes car once and I had to take off the rear wheel to get it to fit in the trunk - perhaps that was when the problem started?

I know if I feel the binding the sprocket will get eaten. And if I added spacers... the binding got worse!

So, I removed spacers instead to try and shift it the other way I removed the BB cover shield (the part the sprocket spacer seats into). This puts the sprocket spacer directly against the BB bearing but leaves the BB bearing with no shield.

It works. Chain spins silky smooth, both directions. It doesn't look any straighter to the naked eye, but the binding is gone and it rolls nice.

It also turns out that BB kits are cheaper than sprockets so worst case I start buying those every few months smile

New tech can't beat old school cool...or can it?
1987 O.O.S. Redline RL20II (Old Old Stock - this ain't no museum piece kids!)
2012 Norco Deviant
1996 GT Avalanche LE w/ Full 2002 XT upgrade and NE Total Air MZO fork

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Oldguyjon Oldguyjon
7/25/2017 9:09 AM

Sprocket #2 eaten by...maybe poor chain alignment, to be determined:
Photo

Photo

New tech can't beat old school cool...or can it?
1987 O.O.S. Redline RL20II (Old Old Stock - this ain't no museum piece kids!)
2012 Norco Deviant
1996 GT Avalanche LE w/ Full 2002 XT upgrade and NE Total Air MZO fork

| Quote
weegaz22 weegaz22
7/25/2017 9:39 AM

Good stuff john, glad you have been able to sort it out, could be there's a spacer missing off the back wheel somewhere if you've had that off, which in turn would move the chain line over a bit, either way you have a bit better idea of whats causing the binding, looking all the way along the top of the chain from the back of the bike it should be straight, if it's not then there's still something probably not right, but least your on the right track instead of being stumped about whats causing it.

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dave lawrence dave lawrence
7/25/2017 11:11 AM

You won't need to replace your BB every few months if you wipe your bearings off-sealed bearings already have shields on them and tend to do a fine job keeping a lot of the gunk out.

I overhaul my BB about 2 times a year. My last BB was from 2006 or so, and lasted through 4 frames before I swapped it (and cranks) for some Odyssey Twombolts a bit over a year ago.

"Hey anybody ever make that mistake like right when you wake up in the morning and you believe in yourself?" -Kyle Kinane

"BIKES!" -Tom Segura

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