Cranks occasionally Slip when riding (chain too loose maybe?????)

[jpb]

Went for a ride the other day and noticed that when i pedal and the crank arms reach the top, it feels like they slip and no power is put to the chain. Had another ride yesterday (around 38 miles) and it kept doing the same thing. it gets pretty annoying as it takes more energy to pedal.
Think this may be down to the chain being too long. I had an ultegra 6700 double chainset with a chain then switched to a compact chainset. I bought a new chain too and used the old chain length as the same length for this one. Could this be my problem or is there other areas to look at????

Any help is much appreciated. Thanks

 

[RecordAceFromNew]

Your sprockets are probably too worn for the new chain. See section here on Chain and Sprocket Wear.

In addition to over-long chain in this case you might also have an issue with violating rear mech capacity. For that this might help identifying.

 

[mikmurray]

i had the same problem, and it turned out that a corner of one of the links on my chain had snapped, and was making my chain jump, i just took the broken link out and replaced it, just a thought to check all your links both outside and inside your chain. hope its that, cos its dead easy to fix

 

[jpb]

I'll check the links on the chain. the sprockets are nearly new too. all the components have only done around 100 miles.

 

[jpb]

Forgot to mention that when I do go out on a ride. The chain does come off once each ride. Thought this would be important to mention.

 

[mikmurray]

its a matter of elimination, you just gotta check all possibilities, i know it may seem crap to do, but you'll find the reason for your problem, loose chain? broken link? slight bend on a cog tooth? hope you get some more ideas from here