New chains and sprockets won't work

[Anthony]

I wonder if anyone with experience of this can help me please?
My bike basically works, the only problem is that the chain has stretched 1/8" and should be replaced.
So I fitted a new SRAM 991 chain. All fine on the stand, but when I put my foot on the pedal to set off, the chain didn't engage with the sprockets, just skated over the top of them. Not skipping between sprockets, just skating round the sprocket, so no forward movement.
The cassette (M770) looked hardly worn, but nevertheless I fitted a new one. Same result.
I've used SRAM chains and XT cassettes/mechs for over 20 years and never had any compatibility issues. Even so, I bought an SRAM cassette. Same result.
I've tried two other chains, one new, one very slightly worn. Same result.
I've tried cleaning the preservative wax off the new chains and triple-oiling them. Same result.
I've replaced the (XT) rear mech. Same result.
I've checked the frame but it's sound.
Re-fitted the old worn-out chain and the part-worn cassette, bike works fine.
I'm now at a loss as to what to try next, but I can't continue with the worn-out chain indefinitely.
Has anyone had a similar experience and/or any helpful suggestions please?
many thanks

 

[Yogi bear]

Are you sure it is the chain slipping on the cassette and not on the chainrings?

 

[Anthony]

Re:

Yes, I can see it!

 

[greencat]

I agree with Yogi, I'd try new chainring(s) wedded to your new cogs and new chain. Then consider fitting the old gear back and running it into the ground as it sounds like cogs, chain and chainring(s) are all worn past the point of reusing any of them with new stuff.

 

[Anthony]

Easier said than done!
Thanks for the suggestion, but can you explain why you think that might make a difference please, as I can't see it?
I should have said incidentally that it's the same in all gear combinations.
I have a sense that if I could get any forward motion, and could ride it at all, maybe after 20 or 30 miles the new chain and cassette would bed in together, but at the moment it won't go 20 or 30 inches.
Oh, and the sprockets are not visibly different from the new ones.
Nor are the chainrings anywhere near worn out, just the chain.

 

[mk one]

Hi Anthony.

I have seen a few people in the past complain of bent 991 chains, also stiff links, which will make the chain skip round the cassette. Also read a about chain length causing sliping which was sorted by shortening the chain.

Mark

 

[greencat]

I am presuming all the gears work fine with any of the combinations you've tested above when bike is upside down/in stand. If not, I would be looking at indexing or a stiff link. A stiff link seems unlikely given the number of different chains you've tried (unless you are reusing the same power link - these can wear too). Indexing also seems unlikely as you clearly seem to know what you are doing.

If that's all good, I immediately get suspicious of the remaining elements of the drive chain ie the chain rings.

Chainrings wear just as cogs do. If the teeth look hooked or pointy, there's a good chance they are worn out.

http://www.wheeliecyprus.com/drivechain.html

 

[ishaw]

Re:

Is it an issue with the indexing? If the new cassette is slightly out from the original one, the chain will be out when changing gear. As someone has said, you seem to know what you are doing, but just in case.

Are the jockey wheels worn? Chain too close to the cassette ?

 

[Corblimeyguv]

Re:

Indexing sounds out.

 

[Bullpup]

Have you thought of adjusting the B tension screw?