The chain keeps snagging on the sprocket...

[Nahom]

I ran the engine but as soon as I ran it the chain kept coming off immediately. I screwed the sprocket cover on disengaged the engine by pulling in the clutch lever so that the wheel could spin freely and I could see how the drive chain was spinning.
Sorted out tensioner proximity to the spokes, pulled in/out accordingly until the chain would spin without coming off the sprocket instantly.
Then just kept rotating pedals really fast to mimic the speed that the chain would go if it was being propelled by engine. It would spin well for about 10 revolutions of the chain then boom there'd be a jam which I couldn't figure out till I opened sprocket cover and noticed the above pic.
After every jam I undid the master link clip - fixed chain position on the sprocket.
Tried again- it would spin well then boom deja vu.
I open cover and pic above once again 5 times this has happened
what could be causing this?

 

[Timbone]

Chain too loose. If you do a search there are threads on this site about how you can clean up that part and make it harder to catch like that.

 

[Nahom]

Chain too loose. If you do a search there are threads on this site about how you can clean up that part and make it harder to catch like that.

Oh I see thanks- notice the top of the chain bouncing up and down like crazy- I assume that snag happens when the top of the chain jumps up off the sprocket then is trying to rotate over sprocket at same time and then jams like that.
So just moving tensioner along the chainstay towards the rear wheel big drive chain sprocket and/or pushing that white cylinder pulley kind of thing upwards as high as it can go on the tensioner will increase the tension in chain so much less play?

 

[gary55]

That's a bingo on both, but try the latter first. If it won't go up high enough to tighten chain then drop it back down to where you can still get a wrench on the top clamping bolt of the tensioner and move the whole thing back.

 

[Nahom]

Beautiful thanks- will try it and update on whether problem is solved.

 

[gary55]

You should be good. I see this a lot. Might wana check the rear tire. It's probably in bad shape with that many sudden stops. Hate to get the chain prob. fixed then trash a rim with a blowout.

 

[crassius]

I note also that you have the sprocket with the flat topped teeth - if all else fails, one can file those teeth to be more pointy at the top which lets the roller of the chain drop down easier (some heavy duty 415 chains have very fat rollers)

 

[Nahom]

cheers for tip- will do helpful extras once all the basics are done.
haven't actually gone back to working on it - what happens if the chain is TOO tight- what problems occur?

 

[gary55]

Bad for bearings. Creates extra resistance in drive train. Chances are the sprocket is not perfectly centered so find the spot where it is tightest by rolling it forward and set tension there. Width of the chain up and down.

 

[crassius]

a chain too tight can force the tensioner down into spokes