Metal scrapes next to sprocket

[FS]

Hi,

Second time I find metal scrapes on the bike right next to front sprocket (first time I cleaned it off). After first time it appeared it seemed ok (no new metal) for a few days. Now it's back. Maybe it's just aggregating slowly.

I can see no obvious damage to sprockets.

I can see some metal missing and some wear on the "outside" of the chain (the part furthest from sprocket centers. That could be from the chain guard - the chain has started to "eat" into the guard (made of plastic I think). When the chain jumps (thumper with a bit uneven power diddtribution) the outside of chain hits the chain guard, which I guess is the point.

A mechanic in Croatia told me something might have bumped up from the road and crushed on the chain but I'm not so sure about that...

Bike seems to work fine, but not so nice finding pieces of metal near sprockets.

Any ideas?

[*Touring Ted*]

Possible reasons.

Your sprocket is too big for the bike.

The sprocket is fitted backwards.

The chain is too big for the sprocket or vice versa.

The counter-shaft splines are worn making the sprocket pivot/tilt.

Chain too tight (stretching and wearing splines) or too loose (flapping about)

[chris]

Tying in with Ted's comments above, if it's caused by "not correct" interaction between the chain and front sprocket, also check rear sprocket carrier bearing(s). If they're shot, wierd stuff will also happen to the front sprocket because the back sprocket is doing things it's not meant to.

[FS]

The sprockets look flawless. No metallic or unusual wear showing where it shouldn't be as far as I can tell.

Yesterday I did first bike clean after 7000+ km and saw that the chain jumping (due to slightly loose chain and uneven thumper power?) has not only eaten into plastic on chainguard, but also slightly into the swing arm where the chain passes over it to go to front sprocket.

A magnet would have been good to have, since I think swing arm is alu..

I have spare chain and sprockets with me. I think I will just keep an eye on the swing arm and keep going if there is no well known serious problem related to finding these metal shards. Of course it shouldn't be there but a lot if things happening to bike... Broken speedometer, bent parts all over the place etc

I guess I could tighten chain a little but not sure I want to mess with that since it has worked well so far on my trip and most stuff I do on the bike info for the first time (=risk of messing it up even more). Chain jumping is maybe to be expected on a thumper that hasn't got a too tight chain... I try to use gears in a way that minimizes it.

Thanks for the advise. It gives me a little more confidence that even though it might be serious, there is no obvious and common issue going on. Being a beginner on this, I guess sometimes you have to just close your eyes, twist the throttle and hope for the best.

Thanks again! I will keep an eye on how it develops. Now into Georgia

[Jens Eskildsen]

Sounds like you sorted it out. Get a new chainslider so you wont end up with a broken swingarm.

[FS]

Just to close this "issue".

I continued riding and continued getting small metal scrapes for more than 10 000 km after the posts above. Probably not good but apparently not catastrophic. I still dont really know what it was/is.