Chain stretch?

From that photo, it looks like the chain is too long - has too many links in it. As the derailleur's spring has rotated it all the way to such a loose position. Chain stretch is not the same thing and is simply terminology indicating wearing of the chain rollers and pins that causes the rollers to have too much play and not fit on the teeth tightly any more. But it doesn't make the chain that much longer.

This should explain it:

livestrong.com406138 when to replace a bicycle chainOpen ↗

Can you take another picture of the derailleur with the chain on the largest chain ring and on the largest cog. (Largest rear gear.) When on the largest chain ring and largest cog the rear derailleur should be stretched out forward not quite parallel to the chain. In this scenario, there should still be just a bit more rotational give in the derailleur. If the derailleur is not close to totally extends when on large to large, then your chain is too long.

Here's a video that should illustrate it for you and you might simply have to remove some links to get it correct.

Quoted post said:

Originally Posted by samg123 [IMG]/img/forum/go_quote.gif[/IMG]

I bought this bike, described as the gears 'running perfect'- when I recieved it I discovered that what I think is chain stretch has caused there to be so much play in the chain that the rear derailleur kicks back and causes the chain to rub over the upper cog on the derailleur- I hope you can see what I mean by the picture.

My question is, is this caused by chain stretch and therefore a sympton of an old, worn out drivetrain?
If this was occuring on your bike, would you describe it as 'running perfectly'?
Im currently involved in a claim against this guy on Ebay, so I'm basically checking that my argument stands up.

I'll be back soon with photos of the corroding crown of the fork (The seller maintains that aluminium cannot corrode)...

First, turn the bike over since the upside down shot doesn't tell the whole story.

Rather than have us try to pick the bike apart piece by piece, why not just wheel the thing to a nearby bike shop, have them put it on the stand, and write you an estimate on what it would take to make it roadworthy? At most shops estimates are free.

Quote:
Originally Posted by samg123 [IMG]/img/forum/go_quote.gif[/IMG]

I bought this bike, described as the gears 'running perfect'- when I recieved it I discovered that what I think is chain stretch has caused there to be so much play in the chain that the rear derailleur kicks back and causes the chain to rub over the upper cog on the derailleur- I hope you can see what I mean by the picture.

My question is, is this caused by chain stretch and therefore a sympton of an old, worn out drivetrain?
If this was occuring on your bike, would you describe it as 'running perfectly'?
Im currently involved in a claim against this guy on Ebay, so I'm basically checking that my argument stands up.

I'll be back soon with photos of the corroding crown of the fork (The seller maintains that aluminium cannot corrode)...

FWIW. Based on the picture, I agree with AlanG that the problem is possibly the chain being too long ...

BUT, a partial remedy which you can implement simply involves adjusting the B-screw which is on the backside on the rear derailleur so that the rear edge of "elbow" is closer to parallel to the rear seat stay than it currently is ...

The chain may still be longer than it needs to be, but adjusting the B-screw should stop the chain from tracking back on itself in the bike's current configuration.

• IMO, it is often easier to adjust the B-screw when the derailleur is not attached to the frame
  

BTW. Without knowing what the text of the eBay listing was other than including the phrase "running perfectly" I have to say that if the chain rubbing when it is probably on the small-small combination is the only thing that is wrong (besides the road grime -- a wiser seller would have cleaned the bike off before he packed-and-sent it) AND if the shifters work well, then you probably just need to clean the bike off & make the necessary adjustements (e.g., saddle height, handlebar angle, brake lever location, etc.) to make the bike comfortable for you to ride and the description of "running perfectly" may not be (particularly in light of how SOME LBS Wrenches adjust bikes!) as inaccurate as your first impression suggested.

And, while aluminum CAN corrode, it cannot rust ... so, you are-or-were probably looking at road grime.

I wonder if the original poster ever read anything we posted.

Quoted post said:

Originally Posted by AlanG [IMG]/img/forum/go_quote.gif[/IMG]

I wonder if the original poster ever read anything we posted.

When it's obvious the poster hasn't done any homework, I don't get technical and I don't get worked up. In this case--pointless photograph and disjointed questions--the situation was pretty clear.

Quoted post said:

Originally Posted by oldbobcat [IMG]/img/forum/go_quote.gif[/IMG]

When it's obvious the poster hasn't done any homework, I don't get technical and I don't get worked up. In this case--pointless photograph and disjointed questions--the situation was pretty clear.

That is a wise view I'll try to adapt before wasting my time in the future.