Chain Drive is Catching/Jumping

[abraxas]

So I have been having some problems with my chain jumping at low speeds when the bike is on the centerstand in 1st gear.  It either started happening when I readjusted the tension or before without me noticing. Maybe related maybe not, my rear bearing has been a little noisy and I plan on replacing it, as soon as the Pony Express delivers my Bikebandit order....

So far I have:

loosened the chain back to the slack limit
tightened it to the minimum slack limit
tried to use a string test to confirm the alignment markers were correct, this seemed ok...
re-degreased and regreased the chain
inspected both sprockets teeth, every chain length in detail
removed the front sprocket for more careful inspection

and none of these have helped get rid of it.

I have tried taking some low quality videos, any help anybody could give me would be great.  i am a complete newb so maybe I am just missing something obvious...
Thanks.

http://www.youtube.com/watch?v=eo6b9hNE3Hc
http://www.youtube.com/watch?v=tSCBNKs93Jo
http://www.youtube.com/watch?v=rqh2ELzAVzA

[DoD#i]

1: if it only happens when not riding (on centerstand? Why are you running the bike in gear on the centerstand?), perhaps it's not a problem.

2: take chain off and check for sticky links (link that does not like to bend, or likes to stay bent - does not move freely).

[abraxas]

Thanks for the reply.

I was running the bike in gear on the centerstand just to check everything out and make sure it was ok, is this a bad thing to do?

I have inspected the chain while it was off the front sprocket looking for a sticky link but didn't find one, but this could be a possibility.

I took it for a ride just now and besides a series of crummy luck (stalled it 3 miles from home after draining the battery today) it seems to be running ok.  There is some noticeable weakness surging in first as I get going, but it disappears as the bike gets power. 

I think I might try replacing the chain, as i would like to try a 15tooth front sprocket.  Seems like the consensus is that I don't have to replace the rear sprocket with a new chain?

[the mole]

I think if the only problem you have is that the chain is jerky when its in gear idling on the centrestand, then you don't have a problem. There's no load on the motor, each cylinder is giving a power pulse every 2nd revolution, so the engine is speeding up/slowing down between power pulses. This is causing the chain to snatch because its trying to rev the back wheel up and down as well, and there's a lot of rotational inertia in the wheel. It would probably happen less if you revved the engine above idle or bought a 4 cylinder bike or added a heavy flywheel. I'll bet if you revved up to say 4,000rpm and put the back brake on a little and kept the revs up there it wouldn't do it at all. Or try taking the spark plugs out and turning the motor with the starter while its in gear. No power pulses=no snatching.
If it still snatches, maybe one of the sprockets is out of round (check chain tension, turn wheel a little, check again a few times).

You can change either sprocket without changing the chain as long as its not worn. If there is significant wear on sprockets or chain, you should change them all, or the one you didn't change will wear the other components. Generally you'd be better off not using too small a front sprocket as that will encourage wear, so if you're going to replace everything keep the 16 on the front and use  a bigger back. If your chain and sprockets are still good, then its cheaper and easier to just try a different front sprocket. I just changed my front to a 17 tooth (after 7,000km so not much wear) and I'm loving it for highway use. Off the highway I mostly don't use 6th gear, so less changes to do.

[08GSSteve]

Your chain looks a little over tight?

I know you have checked the chain but it still looks overtight to me

May just be the low res video

[DoD#i]

I was running the bike in gear on the centerstand just to check everything out and make sure it was ok, is this a bad thing to do?

I have inspected the chain while it was off the front sprocket looking for a sticky link but didn't find one, but this could be a possibility.

I took it for a ride just now and besides a series of crummy luck (stalled it 3 miles from home after draining the battery today) it seems to be running ok.  There is some noticeable weakness surging in first as I get going, but it disappears as the bike gets power. 

I think I might try replacing the chain, as i would like to try a 15tooth front sprocket.  Seems like the consensus is that I don't have to replace the rear sprocket with a new chain?

It's designed to work with a load on. While you need to run the engine on the centerstand for such things as carb balancing, it's a poor idea to put the bike in gear on the centerstand, IMHO. Put it in nuetral, spin the tire by hand, if it all looks good, take it for a test drive.

If you already inspected the chain for a sticky link and did not find one, there probably isn't one.

If you have not dropped some carb cleaner in the gas, try that as a first cut - "surging" probably means something is not quite right, and ultimately you should at minimum check the float levels and balance the carbs (search the FAQ section). Pull the plugs and see what they look like - similar or different? Compare to "good" and "bad" pictures. Sanity check - common mistake - riding off with some choke on to finish warming up in first mile or two of riding, then forgetting to push choke all the way off? Or choke mechanism not shutting all the way off when lever is pushed all the way off - these both can create some strange behavior.

The golden rule of changing chains is that all parts showing wear should be replaced at the same time. If your rear sprocket does not appear to be worn, you probably don't need to change it - but if it is (look for things like teeth that are not symmetric - different shape on front and back of tooth) you want to change things out as a set. Once you get a feel for how long a set lasts, it is usually possible (I have not checked if there's some reason this would not work on a GS, so someone correct me if it won't) to turn the sprockets around about half-way through their life for slightly longer wear.